Bryan Cardella

Evolution

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Table of Contents

Section 1: Introduction to Biology

Scientific Method

26m 23s

Intro

0:00

Origins of the Scientific Method

0:04

Steps of the Scientific Method

3:08

Observe

3:21

Ask a Question

4:00

State a Hypothesis

4:08

Obtain Data (Experiment)

4:25

Interpret Data (Result)

5:01

Analysis (Form Conclusions)

5:38

Scientific Method in Action

6:16

Control vs. Experimental Groups

7:24

Independent vs. Dependent Variables

9:51

Other Factors Remain Constant

11:03

Scientific Method Example

13:58

Scientific Method Illustration

17:35

Biology Evolution

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Section 4: History of Life: Lecture 1 | 1:47:19 min

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	0 answers Post by Jane Lou on January 21, 2019 thank u
	0 answers Post by Bryan Cardella on December 28, 2018 NOTE: Just to clarify - saying that "evolution takes a long time to occur" is true when talking about macroevolution (and speciation.) BUT microevolution, the changes that occur in allele frequencies from one generation to the next, happens quickly. There are gradual changes that must occur on a small scale to get to the big changes on a geological history-level scale.
	2 answers Last reply by: Bryan Cardella Mon Jun 29, 2015 3:16 PM Post by Hossain Khondaker on June 28, 2015 is it wrong to disagree with the theory of evolution??
	0 answers Post by Shahram Ahmadi N. Emran on June 21, 2015 I wish you were my ap biology instructor on educator.com.
	1 answer Last reply by: Bryan Cardella Mon Jun 22, 2015 11:18 AM Post by Shahram Ahmadi N. Emran on June 21, 2015 thanks
	1 answer Last reply by: Bryan Cardella Sun Oct 19, 2014 2:24 PM Post by Abuk Chol on October 19, 2014 why does it takes so long to load?
	1 answer Last reply by: Bryan Cardella Sun Jun 15, 2014 12:14 PM Post by David Saver on June 14, 2014 How did the DNA coding system arise without it being created? How does a Genetic INFORMATION system arise by itself? What kind of information writes itself??????
	1 answer Last reply by: Bryan Cardella Sun Jun 15, 2014 12:05 PM Post by David Saver on June 14, 2014 Ernst Haeckel was accused of FRAUD and intentional deception for these drawings. The drawings contain errors intended to emphasize embryonic similarity and support recapitulation theory.

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Evolution

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

Intro

The Scientists Behind the Theory

Darwin's Voyage

Natural Selection Summary

Evidence for Evolution

Patterns of Evolution

Gradualism vs. Punctuated Equilibrium

Modes of Selection

More on Sexual Selection

Notes on Natural Selection

Reproductive Isolation

Reproductive Isolation (Post-Zygotic)

Speciation

Adaptive Radiation

Hardy-Weinberg Theorem

Microevolution

Clarifications About Evolution

Intro 0:00
The Scientists Behind the Theory 0:04

Fossil Study and Catastrophism
Gradualism
Population Growth
Early Evolution Thought
Natural Selection As a Sound Theory

Darwin's Voyage 8:59

Galapagos Islands Stop
Theory of Natural Selection

Natural Selection Summary 12:37

Populations have Enormous Reproductive Potential
Population Sizes Tend to Remain Relatively Stable
Resources Are Limited
Individuals Compete for Survival
There is Much Variation Among Individuals in a Population
Much Variation is Heritable
Only the Most Fit Individuals Survive
Evolution Occurs As Advantageous Traits Accumulate

Evidence for Evolution 19:47

Molecular Biology
Homologous Structures
Analogous Structures
Embryology
Paleontology

Patterns of Evolution 40:14

Divergent Evolution
Convergent Evolution
Co-Evolution

Gradualism vs. Punctuated Equilibrium 49:56
Modes of Selection 52:25

Directional Selection
Disruptive Selection
Stabilizing Selection
Artificial Selection
Sexual Selection

More on Sexual Selection 1:03:00

Sexual Dimorphism
Examples

Notes on Natural Selection 1:09:41

Phenotype
Only Heritable Traits
Mutations Fuel Natural Selection

Reproductive Isolation 1:12:00

Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Gametic Isolation
Geographic Isolation

Reproductive Isolation (Post-Zygotic) 1:18:37

Hybrid Sterility
Hybrid Inviability
Hybrid Breakdown

Speciation 1:21:02

Process in Which New Species Forms From an Ancestral Form
Factors That Can Lead to Development of a New Species

Adaptive Radiation 1:24:26

Radiating of Various New Species
Changes in Appearance
Examples

Hardy-Weinberg Theorem 1:27:35

Five Conditions
Equations

Microevolution 1:36:59

Natural Selection
Genetic Drift
Gene Flow
Nonrandom Mating

Clarifications About Evolution 1:41:24

A Single Organism Cannot Evolve
No Single Missing Link with Human Evolution
Humans Did Not Evolve from Chimpanzees

High School & College General Biology

Section 1: Introduction to Biology
	Scientific Method	26:23
	Molecular Basis of Biology	46:22
Section 2: Cells: Structure & Function
	Cells: Parts & Characteristics	1:12:12
	Cellular Transport	32:01
	Cellular Energy, Part I	52:11
	Cellular Energy, Part II	40:50
	Cell Division	1:09:12
Section 3: From DNA to Protein
	DNA	51:42
	RNA	51:59
	Genetics, Part I	1:15:17
	Genetics, Part II	49:57
Section 4: History of Life
	Evolution	1:47:19
	Human Evolution	47:31
	Origins of Life	40:58
	Biogenesis	27:25
Section 5: Diversity of Life
	Taxonomy	35:21
	Viruses	44:25
	Bacteria	46:01
	Protists	32:46
	Plants, Part I	54:22
	Plants, Part II	44:40
	Fungi	26:20
	Animals, Part I	35:28
	Animals, Part II	48:42
	Animals, Part III	35:45
	Mammals	38:39
	Animal Behavior	29:55
Section 6: Ecology
	Ecology, Part I	1:07:26
	Ecology, Part II	50:50
Section 7: Laboratory
	Laboratory Investigation I: Microscope Lab	24:51
	Laboratory Investigation II: Egg Lab	11:26
	Laboratory Investigation III: Carbon Dioxide Production	14:34
	Laboratory Investigation IV: DNA Extraction Lab	10:38
	Laboratory Investigation V: Onion Root Tip Mitosis Lab	13:12
	Laboratory Investigation VI: Inheritance Lab	13:55
	Laboratory Investigation VII: Allele Frequencies	14:11
	Laboratory Investigation VIII: Genetic Transformation	16:42

Transcription: Evolution

Hi, welcome back to www.educator.com, this is the lesson on evolution.0000

Before we talk about evolution, what we know about the theory of natural selection0006

and how it has affected life for billions of years on planet earth,0010

let us talk about the scientists who have lead to us understanding what evolution is.0013

First to start with Georges Cuvier, had a lot to do with fossil study and catastrophism.0018

The guy really knew this fossils, did a lot of studying the fossils, excavating.0024

He had this belief in catastrophism, come from the word catastrophe.0030

He believed that major changes in the fossil lineage of how you get from one era to the next,0035

had to do with major and natural disasters affecting species in a big way.0042

Mass extinctions and stuff like that.0048

Back in his day, that view was very revolutionary.0051

He really did not know what he is talking about.0057

This fossil study and catastrophism combination did influence Charles Darwin.0060

Charles Darwin read the works of Cuvier that definitely led to his background knowledge regarding where life came from.0066

James Hutton, kind of the opposite view of Cuvier, in the sense that0073

instead of talking about major events that had a huge dramatic impact on life, in terms of changing it.0078

Gradualism was what he favored.0086

You will see later on this lesson there is a gradualism view vs.0089

what is called punctuated equilibrium which goes along with that catastrophism view.0093

Gradualism definitely counters the catastrophism.0098

It is something that says that gradual changes over millions of years or thousands of generations,0103

gets life into various forms overtime and results in different species.0111

Hutton, little different viewpoint than Cuvier.0117

Thomas Robert Malthus, oftentimes just by Robert Malthus, had a big impact on not only science0120

but economics with his views on population growth.0127

He have a lot to say about what happens to population growth, when there are not enough resources to sustain the population.0131

And the negative consequence of having too many individuals for what is available in that area.0139

Definitely, it has an impact on natural selection and the ability of species to be successful in an environment.0146

Malthus had an impact on multiple fields of study.0152

Jean-Baptiste Lamarck, had a lot of impact on Darwin because he came just before Darwin, born in the 1700’s, Darwin born in the 1800’s.0157

Lamarck had some thoughts and some writings that definitely influenced Charles Darwin next.0170

Here are two things he had to say.0177

I'm paraphrasing but these are general viewpoints of Lamarck.0179

Use vs. disuse, we know that use vs. disuse has legitimacy even today, when we look at natural selection.0184

They use side of it is saying that, if an organism uses something and it is useful to them,0191

it is probably going to last from generation to generation.0197

It is going to be passed on, it will be retained in the species.0199

Possibly, exaggerated and enhanced over time.0203

For instance, giraffe neck length, if you look at the ancestors of giraffes, their necks were not nearly as long, not even close.0207

Going back millions and millions of years, how do you explain how do you get to the modern day giraffe.0216

If there was an environmental change that made it,0221

whether there is a drought that affected the leaves that the giraffes ate or the ancestors of the giraffes.0224

Perhaps, there are less leaves in the trees.0231

If there was an individual in the giraffe population with a slightly longer neck,0234

who can reach slightly more leaves, and the rest are practically starving.0238

The one that can reach slightly more leaves is going to be that much more healthy,0243

is going to have more mates because it will more healthy and robust.0248

Have more offspring pass on the genes that had to do with having that slightly longer neck.0252

If you continue a pattern like that over many generations, if you extract the layout of that pattern,0257

you could see how gradually there could be an increase in the size of the vertebral bones0262

in the cervical region of their spine which lead to longer next size overtime.0268

Now, you are at the point where all giraffes have long necks,0273

and they are still born with what now we considered a birth defect having a shorter neck as a giraffe.0277

Disuse, the disuse thing definitely applies as well.0283

The human appendix, full name would be the vermiform appendix,0290

is this little tiny sac that comes off of the beginning of the large intestine, the colon region.0297

That sac can be removed through an appendectomy, if it gets infected via an appendicitis.0306

No big deal, you do not need it to live.0312

It is considered a vestigial structure, it is vestigial, you do not need it.0314

It is a remnant of something from my ancestor.0323

This is an example of the disuse thing.0325

The best theory I have heard regarding the occurrence of this useless appendix is,0327

our ancestors from millions of years ago who did not cook their meat, who did not cooked food.0333

They have not mastered the use of fire yet, they would have needed enlarged sac in that region of their digestive tract0338

to better deal with the bacteria and other things that would be in that meat, as it goes to the digestive tract.0346

Once you have cooked meat and kill off bacteria and other microorganisms, you do not really need it as much.0354

Once they started cooking meat over thousands and thousands of generations, gradually got reduced in size.0361

Maybe a million or two million years from now, the appendix might disappear.0371

It is hard to say, it is just a guess.0376

There is the use and disuse that Lamarck observed and theorized about.0378

However, the inheritance of acquired traits, this is not true because acquired trait is something you get or obtain after you have been born.0384

You have acquired it, it was not inborn, it was not inmate, it was not in you to begin with.0399

What you pass on to your offspring is what is in your DNA, what is actually in the cells that you are passing on.0404

The viewpoint that acquired traits are inherited would be like me saying, if I lost an arm0412

and then had kids, my children will be more likely to have 3 limbs instead of 4.0417

We know that is ridiculous.0422

Or Arnold Schwarzenegger, meaning if acquired traits were being inherited0424

that would mean that his kids would come out with greater likelihood of being able to lift weights.0432

That is not true, if his children want to be just as good at getting the Mr. Universe contest win,0438

they have to lift just as much weight and have to take this as many supplements.0447

It is not true that acquired traits are passed on or inherited.0452

Acquired traits can definitely make it more likely that you are going to have successful offspring.0457

Because if you acquire an ability or trait and develops in you as you are living,0461

you are probably more fit in the environment in terms of having mates pick you0467

and having more offspring and taking care of his offspring, if you are a bird or a mammal.0472

What Lamarck contributed is use vs. disuse idea.0479

We now know that the second point is not true.0482

Charles Darwin, definitely the father of evolution, in terms of what we understand today.0485

His theory of natural selection, a lot of it was theoretical when he wrote it in the mid 1800’s.0493

The amazing thing is after all this time has passed, almost 200 hundred years since that has been published,0501

a lot of what he theorize has now been supported and verified via evidence that he did not see.0510

He just had these good ideas about connecting the dots between what we observed.0517

He proposed natural selection as a sound theory, I do not mean a sound theory,0522

I mean sound is in really good, reliable, good theory of natural selection.0525

There is the most famous image of him, older Darwin, after as his famous book was published.0533

Darwin's voyage, Mr. Darwin sailed around the world for about 5 years at the age of 22,0541

when most people would be graduating from college.0546

On the H.M.S. Beagle, HMS his or her majesty ship, indicating it was a British vessel.0548

They definitely set sail from the UK, from Great Britain.0556

Darwin, a quick background about him, his father was a physician, very well respected physician, pretty wealthy.0560

Back in those days, especially, it was expected that your son would carry on the father's work.0569

Darwin was not interested in being a physician.0575

From what I read, he found it grotesque, he found it unappealing.0579

He was more interested in just studying life, in general.0583

About why animals and plans are the way they are.0586

Definitely, he had some interest in reading the works of Cuvier and other researchers and scientists.0590

He got permission to go aboard a ship that had a lot of cartographers and map makers,0597

setting sail around the globe, when they circumnavigate the globe much like Magellan did.0604

Slightly different path than Mr. Magellan took, but he definitely set sail with them for 5 years.0608

Here is basically where they went.0614

Most famous stop right here, the Galapagos islands off the coast of Ecuador.0621

Definitely the most famous stop, these are isolated islands and like a lot of isolated islands,0629

they tend to have unique examples of speciation of endemic species, that would be the term.0634

Endemic means you are not going to find them anywhere else, they are native to that place.0640

Endemic species not just finches, not just giant tortoises,0645

all kinds of really interesting animals and plants that you would not find anywhere else.0650

Stopping at all of these island groups, I realized that Australia and New Zealand are not there.0655

That is basically where they went more or less.0664

They stopped at a lot of different islands.0667

Like I told you, the isolated islands that you are not going to have a lot of immigration and emigration of animals and plants,0671

you get some really interesting examples of speciation, which I will tell you more about, later on in this lesson.0677

He gathered all kinds of data, written observations in his journal, sketches, he was a very good artist.0682

Fossils collected those, artifacts from plants and animals.0689

He used these to formulate his theory of natural selection.0694

By the time he got back in his late 20’s, much time went by between him arriving back on British soil.0696

Finally, him, publishing what he had found of and what he had come up with as this formulated theory.0706

He published the book when he was about 50, that is a lot of time0713

between him coming back from his trip and the publication of his famous book.0718

There are theories that, not only did it take him awhile to write it and come up with this really good synthesis of all this material.0722

Some of them, it might have been fear.0732

He knew that his book will be very controversial, when he published it.0734

For the amount of people that will appreciate his book and thought that it was a good theory,0739

he had just this many people if not more, calling him the devil.0745

Saying that, what he was claiming to be true was blasphemy.0750

Here is a summary of what Darwin actually talked about in his book.0758

A lot of people who are opposed to the idea of evolution or natural selection have not been exposed to what really is and what it is not.0761

Evolution is based on physical evidence and there is plenty of physical evidence there to support that this is what has been going on.0774

Darwin published his most famous book on the origin of species, there is a much longer title on the cover of the book.0780

The main part of the title is on the origin of species in 1859.0785

He was born in 1809, he was close to 50 years old when it was published.0789

Interesting point, a side note, Darwin was born February 12, 1809, same exact day that Abraham Lincoln was born.0793

Same exact day, same exact year.0801

It is amazing to think that two of the most important figures with brilliant minds of the 19th century were born on the same exact day.0803

Some points that summarize his work.0812

If we were to take all those pages, so you do not have to read it.0815

What are the main points?0820

Here is 8 major point that summarize his work.0822

Number one, population have enormous reproductive potential, that is reproductive potential not the actual output of offspring.0825

I’m paraphrasing here but he did a calculation based on the gestation, the length of pregnancy from elephant.0835

How long it takes for them reproduce, and then how long it takes an elephant to age to get to reproductive age, and so on.0843

He took those figures and calculated, if you start with two fertile elephants that can have offspring.0851

You let them reproduce and have offspring over and over again, for many decades,0857

you eventually get to the point where you have million elephants.0863

But, are you really going to have million elephants in real life, after that much time?0866

No, why not, because there are going to be limits to that reproductive potential in the environment.0870

There is only so much space, there is only so much material for them to consumer.0875

Not every elephant is going to make it to reproductive age.0879

Not every elephant is going to have offspring every mating season.0882

It is one of those things where the reproductive potential is there but there are limits to it.0888

Going along with it, we can see the population sizes tend to remain relatively stable.0893

Here is an example of what I’m talking about here.0901

Let say here is the number of individuals on the Y axis and here is time on the X axis.0903

Here is a little population curve for you, you can see that at first, near time 0, there is huge population increase.0917

Let us say that right here, this red dotted line, this is what is called the carrying capacity0924

meaning that is the amount of individuals for a population that can be adequately maintained0937

or supported in a particular environment, in terms of resources.0944

Notice that this population went above the carrying capacity for a bit and then there is a quick drop0950

because when you get that amount of offspring repeatedly, just tons and tons of individuals,0956

you get to the point there is not enough space and not enough food.0962

A lot of them are dying because you get to a point where you have influenced the environment0965

whether there is not enough food at all, we have eaten it.0971

There is a lot of death, but then when you get that drop off of individuals,0975

the environment can recover in terms of bringing back that plant life,0980

the other members of the food web that were supporting this population.0985

It is another little boost.0988

Overtime, you get this like undulation of increase and decrease of population size.0990

You can see that as it goes on over time, it tends to just hover on the carrying capacity.0995

Ideally, it will be just below it.1000

Every time you exceed it, you are going to get a drop in the population most likely.1004

Resources are limited, been talking about that with the pass two points.1010

That, resources, whether we are talking about food, space, air, water.1015

If we are talking about plant life, sunlight definitely is a resource.1020

If there is too many plants in an area, the little guys down below can be crowded out and they would not be able to absorb sunlight at all.1024

Resources are definitely limited, there is only so much to go around to support populations.1032

Individuals compete for survival that is obvious.1037

Individuals in a population, the ones that are more fit, the ones that are faster, stronger,1040

able to withstand harsh environments, they are probably going to live longer and1047

they are probably going to have more successful offspring.1052

There is much variation among individuals in the population.1056

By much variation, we cannot always say that there are variations with everything.1059

When we look at one species, what makes them one species is they have numerous characteristics in common.1068

The things that make them stand out from one another, that is what natural selection is going to be acting on,1074

in terms of which members of the population will be more successful than others.1080

Much variation is inheritable, we are using that term much variation again.1086

Not all variations is inheritable because acquired characteristics are not passed on.1091

The things that are in the genes, the things that are actually in the sperm and in the egg,1096

or the pollen and the egg that come together, those are going to be able to be inherited or to be heritable.1100

Only the most fit individual survive.1108

I want to add something here.1110

Survive to reproductive maturity because the reproductive maturity that is what really determines1111

whether or not the animals is going to be passing on its traits to the next generation.1129

Only the most fit individuals survive long enough to have children.1133

An animal can be born and have some disadvantages and make it for a little while but might die off,1139

in terms of like predators being able to easily eat them as prey and pick them off.1146

The reproductive maturity is definite a part of the long-term success of the species and those traits been passed on.1155

Finally, this is kind of an including statement.1164

Evolution occurs as advantageous traits accumulate from generation to generation.1166

It is baby steps, evolution do not happen overnight.1172

With animals, it is not going to happen in a thousand years.1175

It is going to be a very slow process that over time, the accumulation can make major changes.1179

There are multiple pieces of evidence, I’m going to give you some main ones.1188

Evidence for revolution number 1, molecular biology.1191

If you watched the lessons on DNA and RNA, this will be not new to you.1196

The structure of DNA and RNA is essentially the same in all organisms, from bacteria on up to humans.1203

What I mean is, the building blocks, the phosphate sugar base in the nucleic acids of DNA and RNA, is the exact same.1208

What is variable is the bases.1216

How many AGC and T you have and in what order for the DNA bases.1220

Comparing the base sequences and even with amino acid sequences in polypeptides1226

that come from that RNA and DNA, can tell you how closely these related organisms are.1233

Differences in nucleotide and or amino acid structure inform us of that.1238

Here we have got DNA of course, the double helical structure.1243

Here is a chain of amino acids, this is a funny way of representing them.1247

Every single pattern here indicates a different amino acid, like this one and this one are the exact same amino acid.1250

Proline, lucine, tryptophan, serine, there are 20 different ones.1261

There are a lot of amino acids but I have seen this really cool charts that show,1268

let us say a part of the gene for cytochrome C, that is the abbreviation for cytochrome C.1273

You actually can find that in animals and plants.1279

You would see cytochrome versions of it in mitochondria and chloroplasts.1282

If you compare cytochrome C of an animal to a plant, you are going to see a lot of differences1287

because animals and plants are not closely related.1292

They do have a common ancestor very long time ago, over a billion years ago.1295

When you compare closely related animals, you are not going to see as many differences, that make sense.1303

If the two animals split, let us say only 30,000,000 years ago compared to 200,000,000 years ago,1308

there is going to be significant differences.1319

For instance, if we compared cytochrome C in the mitochondria of chimpanzees and humans,1321

you would not see that many differences compared to the total number of amino acids.1328

I do not know that difference number on top of my head but comparing humans and chimps,1333

you would see a lot less differences than comparing humans and tuna fish, or humans and rabbits.1337

Looking at another protein like hemoglobin in red blood cells,1346

looking at certain sequences of the hemoglobin amino acid chain in chimpanzees and humans,1350

you may see regions where there are 0 differences.1355

About 98.5% of chimpanzee DNA is the same as ours.1360

There is that significant difference but just goes to show you that the closer DNA and RNA in the amino sequences are,1365

the more closely related the species are.1373

Evidence for evolution number 2, homologous structures.1378

Homologous meaning same phylum, these are bodily structures that have been modified over time that are from a common ancestor.1380

This structure, a lot of animals they have it in common.1389

As we go through the evolutionary tree, slight modifications on those structures over generations1393

because of natural selection have changed it.1399

You will still see commonalities.1400

They are classically bone, the best examples of homologous structures I have seen are from bones or fossils.1403

My favorite example, a great example, is from vertebrate forelimbs, the front limbs not the hind limbs.1410

Here were comparing the forelimbs of a human, a dog, what is that look like?1419

I will tell you, it is a bird, it might not be very easy to tell without the feathers but that is from a bird and this is from a whale fin.1428

That is why we are comparing forelimbs because modern day whales do not have hind limbs anymore,1437

their ancestors did and there is fossil evidence for that.1442

Here you have color coding of forearm bones and wrist bones, ulna, radius, and the metacarpal region.1446

Here, that is a human, pretty obvious.1458

Check this out, remarkable similarity when we look at the dog version of that.1461

It make sense that they are quite similar because dogs are mammals.1467

They are more distally related to us than something like a pig or monkeys, and stuff like that.1474

Birds, you are going to have modifications because birds had had their forelimbs modified1482

from early reptiles and had been now become wings.1490

It was a gradual process that got you from reptile forelimbs to now bird wings.1495

There you have the similarity/ contrast.1502

Whales, obviously there is a big change in whales, they are mammals.1507

We think they are more closely related, if you want to find whether they are mammal or whales,1512

close to in terms of like analyzing their DNA and amino acids and stuff.1519

The Bowline crowd, cows and hooved mammals actually have a remarkable amount in common with whales.1525

We think that some of ancestor of hooved mammals made its way into a more aquatic kind of environment.1533

Gradually, over time there is modification of the limbs.1543

There you go, the closer the similarity is, the more similar you are going to have in terms of their abilities now.1549

All four of these, you can trace back to early reptilian forms because both mammals and birds are descended from reptile groups.1559

The farther back we go, the more commonalities you would see, in terms of what they came from.1571

Evidence for revolution number 3, analogous structures.1581

Instead of talking about them coming from the same ancestors and getting different modifications of them over time,1584

here we are talking about body structures that have the same purpose but have come from completely different ancestors.1592

It is a flip of the homologous.1599

Homologous, same ancestor different purpose overtime.1601

I think about the purpose of our arms and whale arms and bird arms,1606

but these are different ancestors gradually getting the same purpose overtime.1611

A great example is wings, what it is, is environmental pressures natural selection1617

that is impacting those two completely different organisms or species overtime in a similar way.1622

This is analogous because we cannot say that butterfly wings and this golden eagle set of wings are from the same ancestor.1629

To find a common ancestor between these two, we got to go way back, in terms of where animals came from.1639

They did not come from the same ancestor.1648

How do they both get wings?1651

Slightly different reasons but because wings benefited them both.1653

Like a mentioned earlier, this would have been from a reptilian form.1659

Reptiles, we think some of them gradually had a lengthening, elongating of scale structure to form feathers.1664

The feathers came before flight.1672

Feathers would initially given reptiles running through the forest,1674

abilities to steer quickly and maybe get off the ground for brief amount of time, but not much.1679

Also display, they probably would have been attractive to potential mates.1685

But over time, the bones getting less dense and feathers getting more plentiful, eventually flight would have come.1689

We think that insects, this is the best theory I have heard, may have had a mutation way back when,1698

that would have caused a slightly little extension from the thorax region, the middle region of their body.1707

That would have like a solar panel that would have enable them to absorb heat energy1716

and helped in terms of like the temperature in an insect’s body.1722

Maybe that would benefited them.1727

Overtime, more mutations could made these little kind of like panels to absorb sunlight a little bit longer, a little more full.1728

All it takes is like a mutation that allows them to move these little solar panels, if you want to call them that.1737

Eventually, they could takeoff.1744

That one that can take off for the first time and fly, you better believe it has an advantage from the other ones1747

because it can escape getting eaten and it can have a lot more offspring and live a lot longer.1752

Pass on that mutation that caused that particular movement of the solar panels, now wings.1759

You get to the point where insects with wings are extremely successful.1767

There are so many, hundreds of thousands of species of them.1772

Embryology, evidence for revolution number 4.1779

Each species or vertebrate has a remarkable resemblance in the embryonic stage.1781

If you were to cover-up these two rows, and I ask you to guess what embryos do these come from?1786

If I give you list of the 8 organisms, it would be really hard to do.1793

This is an old drawing from long time ago.1799

Over here on the left side, you see fish, salamander, turtle or tortoise, chick,1803

I believe it is a pig and then you get rabbit and, I think it might be a sheep or cow.1815

You definitely have human on far right.1824

You could tell a little bit more difference as you go into this middle row.1827

Of course, when we get down to the bottom you can tell them apart.1831

Up here, it is remarkable how early on in the embryonic stage you have vast similarities,1834

whether or not the vertebrate is a mammal or reptile, or a fish.1842

This shows you that we all came from the same origination.1848

We all came from the same ancestors.1853

There are leftover things, even in our embryos that do not need to be there1855

but they are still there because they are from our ancestors.1859

Examples, pharyngeal gill pouches or folds, they are also referred to as pharyngeal gill slits.1863

This would form the gills in a fish or the gills in amphibious groups.1869

When we are talking salamanders or frogs, in the tadpole stage they still have their gills.1878

Pharyngeal gill pouches, all these little folds here, they could become gills or not.1883

In us, in the majority of these animals, these go away.1891

They appear briefly in the embryo and then they are gone.1896

In the sense of vestigial structure, left over from our ancestors and1899

those things would be stimulate to remain and develop, before they are hatched or born.1903

It is interestingly thing left over in all of these examples.1910

Limb buds, the limbs vary from animal to animal.1913

These little projections here, these little limb buds they come out just little bumps.1918

As time goes on, the interesting thing is that you have this that looks like a paddle as the hand.1923

If you end up getting this in us, it is because these cells are stimulated to die, these cells are stimulated to die, and so on.1931

That is how you get a hand, it is called apoptosis, programmed cell death or cell suicide.1941

Apoptosis happens in all these animals in some way or another.1953

The point of making that limb buds they all share them but the way that the limb bud gets modified over time is different1957

because you do see differences when you compare fish, salamander, to human.1964

Tail, also known as the post anal tail because it comes out from that area behind it.1970

The tail is not retained in us and in other animals, like when we look at a gorilla or chimps, they also do not have a tail.1978

We do have a tailbone, this stops developing at a certain point embryonically.1985

Whereas organisms like here or here, or here in the pink, it grows longer.1989

The growth is retained.1996

It also do with that gene expression in which genes are stimulating that to happen.1998

But they all have a similar looking tail earlier in embryonic development.2003

When we get to this point, there are those differences.2007

Yolk sac, in my opinion is the most incredible one.2010

We do not mean a yolk because a yolk in an egg is meant to nourish the reptile or nourish the bird before it hatches.2013

That yolk is being absorbed as food, when they run out of it, they will be hungry and they come out of the shell.2023

In us, we are attached to the umbilical cord and placenta.2030

We get blood supply directly from the mother in the uterus.2034

That is true of placental mammals.2037

We do not need a yolk sac, we get blood directly from our mother with the oxygen and nutrients,2041

and then the CO2 and waste products go back out through a vein.2049

Why do we have this yolk sac?2053

The yolk sac is not filled with yolk but there is a remnant that helps form the umbilical cord region and the placenta,2055

and that becomes part of that whole unit.2064

But if you look early on at a human or mammalian embryo, you have this region that2067

if we were looking at a reptile or bird, would be filled with yolk.2073

So does this remnants because if mammals came from reptiles,2077

it makes sense that we would have this retention of certain characteristics.2082

But a gradual morphing on that, a gradual change based on the evolutionary changes.2088

Evidence of evolution number 5, paleontology.2096

I think we are all exposed to some of this as a kid.2099

A lot of kids end up getting infatuated with dinosaurs, they are so cool to learn about and play with.2102

Not real dinosaurs, the toys.2109

This is the study of fossils and it is an obvious indicator of the mechanism of evolution.2112

These things we discovered in the ground from long ago.2118

They are there for a reason, these things used to be alive and they are indicating something about our past.2123

Strata or stratum would be singular, these are the geologic layers in the earth’s crust.2130

Generally, the lower the strata, the longer ago these particular individuals existed.2135

There is a layer upon layer of sediment, as time goes on, sedimentary rock.2142

That is what you are seeing here.2148

Sedimentary rock is a great place to look for fossils, especially where other fossils have been discovered before.2153

Fossils are not going to occur a lot, you need a particular situation for a dead animal or plant, whatever,2162

to have a fossilized imprint or fossilized bone.2172

You need to have a situation where they are not going to be decomposed by a lot of bacteria and microorganisms.2176

You need to have a situation where they are going to be concealed in a layer very quickly upon dying,2181

that is going to preserve those parts.2188

Radioactive dating is a way to figure out approximately how old fossilized parts are.2192

It is all about radioactive isotopes, you may have heard carbon dating, it is not just carbon.2199

It indicates how much of a particular isotope was left in fossilized bone.2204

Isotopes are like different versions of an element, based on how many neutrons are in there.2208

Remember, neutrons they are do not have a charge, they just add to the mass of an atom.2218

Carbon 14 is one of the ones you can test for.2222

There is carbon 12, there is carbon 14.2224

Carbon 14 has two more neutrons than carbon 12, it is a little bit heavier.2228

If you test how much of this is left over in a fossil, that indicates about how old it is.2234

This gradually breaks down into other isotopes.2241

As carbon 14 breaks down, another isotope gets formed.2246

This has a predictable half life meaning, if you traced the percentage of this leftover over time,2250

if you started out with this amount and half way is about here.2262

The half life meaning the amount of time that has to go by to get to the point2269

where half of it is remaining is about 5,700 years for carbon dating.2273

If a fossilized is being is over a million years old, testing for the amount of this is not going to work out because all of this may be gone.2279

It is a much lighter, less massive isotope that more easily degrades over time.2289

That is a short half life.2296

Uranium 235, very different in terms of its half life.2298

To give you an example of how much it can get skewed.2304

Uranium 238, a little bit more massive as the raw version of uranium, has a half life that is over 4 billion years.2306

Uranium 235, its half life is in the millions upon millions of years.2318

If you want to know how old dinosaur fossils are, testing for the amount of this is probably going to be reliable.2326

It takes a longer for this to completely leave, not leave rather breakdown into the other isotope over time.2336

This is a really famous, they would call it a transitional fossil.2349

This is an archeopteryx, let me write that here.2356

This is one of the earliest ancestors of modern day birds.2366

It has reptilian characteristics.2369

The cool thing about this fossil when they excavated it is like, you have almost the whole skeleton in there.2370

You can see these really cool imprints here of wings, you can see that going on.2377

The cool thing is that not only does it have this birdlike characteristic of having wings with feathers but2382

there are evidence of teeth which modern birds do not have.2388

You have an actual bony tail like a reptile would have, with feathers coming off of it.2392

You do not see a long extended tail in birds, you see tail feathers.2398

They have that nub in that back end.2402

You see this transitional form where you still have a lot of reptilian characteristics but2405

it is leading into that modern bird form, we are used to seeing.2409

Patterns of evolution, evolutionary histories pertaining to modern organisms can be summarized in a few ways.2416

This is like looking at the big evolutionary tree which would be so incredibly massive with branches and2421

neighboring branches continuing another branches, neighboring branches coming close together and so on, and so forth.2427

This is zooming into little parts of that evolutionary tree.2432

Divergent evolution, here is a little graph for it.2437

Here on the Y axis will be time.2441

I know normally we do that on the X axis but this is way back when and this is now in modern day.2443

On the X axis, we are going to have variations in morphology.2453

Meaning, the farther away that two points are when we representing organisms evolutionary path,2466

the father way they are, the more different they look.2473

The more different their bodies, the more different what they are doing, the more distantly related, they probably are.2476

The closer they are together, they are the closer their body form is.2483

Morphology is the study of forms.2487

This would be divergent.2493

Here is an ancestors, I’m just going to write A for ancestor.2497

Up on top we have got the modern day version of two, now very different looking animals or plants from some ancestor.2501

Here, let us say we have got a hummingbird and here we have got ostrich.2510

Both are birds right but you can get much different than hummingbird and ostrich, when you are looking at class avis.2523

The birds within the vertebrate group.2531

Hummingbirds very tiny, the tiniest species of hummingbird I have ever heard is called the bee hummingbird.2534

It is like this big.2539

Ostrich, the most massive modern day bird on earth, cannot even fly anymore.2541

It is so massive and its wings are so tiny compared to its body size.2546

Amazing how they both presumably came from a bird ancestor from millions and millions of years ago.2551

That archeopteryx fossil is just over 100,000,000 years old.2557

Now, you have got this, it would have been gradual changes over time that would have separated them.2561

This is just a small example because you have got so many species of birds out there,2567

that would be in between them, in terms of morphology.2574

This is divergent, a splitting over time.2578

Natural selection does that, natural selection will act on different populations in different ways,2582

based on where they are at and what the situation is.2587

How that happens over time to extrapolate the patterns over time.2589

Convergent evolution is very much the exact opposite.2595

I would not say exact opposite but the shape of the graph does look the opposite.2598

Once again, variation in morphology.2608

The reason why it is not the exact opposite is I do not want you to think that these two modern beings are the same species.2612

No, here we have got ancestor A and ancestor B.2620

Up on top this could be, let us say a penguin, I should do it in blue just like I did before, keep the pattern the same.2625

Penguin and porpoise, dolphins are their relatives.2637

By the way, if you want to know how to spell porpoise, weird word, it looks like porpoise.2648

Penguin and porpoise, the reason why I have them as being very close in morphology is,2654

if you compare their fin region, it would really be a wing on a penguin, and their body shape.2662

There are a lot of similarities, even their head shape is very similar.2669

Why, because even though one came from an ancestral bird and one came from an ancestral mammal,2673

living in the same environment or near the same environment for so long, hunting fish, they both would like to eat the same kind of thing.2679

Hunting fish and trying to move to catch those fish in the same way has gradually made them look so incredibly alike,2688

in terms of their streamlined body shape.2695

Penguins, when you look closely at their body, they still have feathers.2701

But it is hard to tell their feathers because they are so reduced in size.2706

And that is important so that they get the movement into the water adequately and not a lot of drag.2709

When you look at the skin of a porpoise or something related to a dolphin, you can see that they are still mammalian.2717

You do not see the feathers, you actually can get little hair follicles in there because they are still mammalian.2726

Over time, two very different organisms can become very much kind of the same.2733

This convergent evolution topic relates to that analogous structures thing.2738

You could also have A as an ancestral bird and B as an ancestral insect,2743

and talk about a bird and an insect that both have this flying ability now.2749

Just keep in mind that these two are not the same, they are different species.2755

They cannot mate successfully.2760

They just surprisingly look similar.2762

Co-evolution, once again, time variation in morphology, here is how it is different.2767

Than overtime their evolution is impacting one another.2785

We are going to say bee and flowering plant.2791

They would definitely be impacting each others evolution over time because they have this mutualism,2800

this dependency on each other.2806

Symbiosis is a term we can use to describe it, but mutualism more specifically.2812

They have a mutual benefit meaning, the bee when it is trying to get the nectar from the flower, ends up getting pollen on it.2816

Pollinates the flower, helps flowering plants reproduce.2823

The flower gets benefit out of that because the bee just wants the nectar, that is how the bee benefits.2828

But, the flower definitely gets the benefit.2834

I’m going to show you on later slide a moth that has an extremely long proboscis.2837

This extension that comes out of its head to get nectar.2842

They can stick it down a very far passageway through a flower to get to the base where the nectar is.2848

The need for that very long extension happen because the flower gradually got this elongated set of petals coming out of the base.2857

It is amazing to look at that.2868

There are actually some flowers out there that look like bees.2869

I had trouble finding an image, a non copyrighted image for you.2873

There are flowers that look very similar to bees.2877

The bees, when they see it and they go and get nectar, it is almost like they are making love to the flower.2881

They are doing this little dance when they are getting the nectar.2886

Bees would not even analyze what they see on a flower.2891

Bees, as far as we can tell can sense UV light.2894

They actually can see it.2898

The UV hitting the flowers makes an interesting pattern on the petals that oftentimes will point in an interesting pattern into the flower.2900

Like, here is where the nectar is, come and get it.2907

They have definitely impacting each other over time.2910

It is not always positive examples, in terms of them both benefiting on another.2912

Another example could be human and tapeworm.2916

It would be the same kind of graph but human and tapeworm.2923

Any animal and a parasite, a parasite depends on the host.2928

To a host’s disadvantage but to the parasite’s advantage.2933

You could say that evolution between us and tapeworms is an arms race,2938

like you would have the two countries try to get better in weapons over time.2942

If a tapeworm invades humans for a while, and then humans are born with a mutation2946

that allows their white blood cells to attack the tapeworm a little bit better and kill it off,2951

that puts pressure on the tapeworm to cover the way to resist those white blood cells.2955

It just keeps happening over time.2960

Now, tapeworms are really good at getting in our bodies and being successful.2962

I just recommend not under cooking pork or shellfish.2967

You will probably not get a tapeworm.2971

It is definitely this arms race that impacted each of our evolutionary paths over time.2974

Please keep in mind that these graphs are not quantitative.2980

I do not have exact numbers here.2984

They are qualitative graphs, they are showing you trends over time,2986

in terms of how organisms evolution relates to other organisms.2990

I hinted that this earlier about the two different schools of thought with Cuvier and Hutton.2998

Gradualism vs. Punctuated equilibrium.3005

In relation to patterns of evolution, the big picture of evolution,3007

if you zoom out from those little patterns I drew in the previous slide, it comes down to these bigger branches.3010

Once again, this is the variation morphology, as we go from left to right.3018

Time is from here, back in time to now.3021

It would be better if these two were side by side but I think you get the picture.3025

These are depicting the same amount of time but different trends with how organisms separated and3031

gained what is called speciation, over time became different species.3039

This punctuated equilibrium definitely goes along with that catastrophism point of view.3043

This is definitely gradualism.3052

Phyla that comes from the term phylum, we will talk about the different animal phyla and other phyla in the kingdoms of life in a future lesson.3055

Catastrophism, catastrophe.3064

Where you get these major changes like that change, this change, that one.3069

You notice that you had this lineage and then all of the sudden, something makes this go way over here.3077

What got them to be so different?3084

You can think of it this way, a catastrophe can eliminate so many organisms,3086

that you get these smaller populations that end up being isolated from one another.3091

Mutations that affect population A which is not separated from population B are very different.3096

Over time, those mutations can make them be different where there is no way3101

they can get back together and reproduce, they become completely different species.3106

This is that more gradual approach, that just tiny little changes over time can gradually cause the splitting.3110

Which one is more true, were they both true.3118

They both have solid examples that exist in the fossil record, both go on.3122

It is just like I said, the big evolutionary tree has incidents or examples where this is going on, that is going on.3129

There are plenty of other examples where this is also going on simultaneously with other species and other forms of life.3138

Modes of selection, we are going to have one big graph for this, that I gradually change depending on which mode we are talking about.3147

Let me do the marker.3156

This is not time now, this is the number of individuals and this is variation in morphology.3162

We are going to start out with a population that matches the classic bell curve look.3181

What this is saying is, we might be talking about, let me make it more close to the 0 line.3193

We might be talking about size of an animal or plant, color, speed, it could be any characteristics.3201

Free to these selection modes, I will pick a specific sample.3213

The basic original population here, we are going to say that black is the original population, at some point in time.3218

This kind of thing keeps happening in the species over time, depending on the environmental conditions.3232

Here is what we are talking about.3238

Natural selection is various ways of selecting which traits are favorable,3239

depending on the period of time, depending on the circumstances.3244

Different traits are favorable at different times, it really depends.3246

In a really snowy region where there is lot of snowing around, having white skin or white fur3251

would be good, whether you are a predator or a prey.3256

You can hide from what you are trying to eat or you can hide from those who are trying to eat you.3260

If the snow goes away and if the period of warming for a thousands of years being white would not be good at that point.3264

Having a mutation that ends up making you look kind of more like the dirt or more like the foliage, that would have been better.3272

Directional selection says that, if you start out with this original population,3280

where like most of the individuals have the medium characteristic, whether it is medium sized, some are small, some are big.3284

Or whether we are talking about speed, most are averaged speed, some are slow, some are extra fast.3292

Directional selection is saying that, it ends up changing like this.3297

It also could be in this other direction.3309

It could be either to the left or to the right.3311

Overtime, the new population ends up being like this.3315

What happen? This could be the giraffe example, that way back when the giraffe neck size,3320

most were average, some were smaller, some were taller.3326

Now it is like nearly all of them have this long neck.3329

There was some kind of pressure, some selection from the environment that selects for a look.3334

Do not think that the environment is like living, there are living parts like plants.3340

The environment does not have this will, I'm going to do this now.3345

We say, it selects for personifying the environment.3349

It means that there are certain things that in point in time that are more favorable.3355

Animals with that particular trait are going to be many more likely to be favored and be successful.3358

Directional section can be the opposite way.3365

Here is an example, there is a reason why a certain insect were very tiny.3368

It is easier for them to hide, it is easier for them to like not be seen by predators that would like to eat those insects.3374

Over time, them being much smaller, a mouse also is an example, has some advantages.3381

That is directional selection.3389

Something in the environment was favoring the traits going in that direction.3391

Disruptive selection, an interesting one.3397

What and how did that happen?3408

It is like there is no more medium, there is no happy medium, they are all light or dark, small or big,3410

slow or fast, that is not a good example.3417

Here are two examples, I’m going to give you one example, for the sake of time.3419

Let us say there is a snail population, originally their shell color was like this.3427

Meaning, most of the snails had this medium brown, some had a very dark, almost black shell,3432

others had a light colored shell, most of them are medium brown.3439

Let us say the environment changes so that it is not this medium brown turf.3443

Some changes in the environment happen where there ends up being a buildup of dark patches,3447

maybe some dark rock and the soil color changes to be very light colored.3452

In that case, you could say that as long as the snails with the light shell hang out around the part that is light colored,3459

and the dark snails hanging out the part that is more that black rock, the medium toned once,3466

regardless where they go, they are going to standout.3473

Birds or whatever are going to eat them because they are going to be seen more easily.3475

Disruptive, it is hard to come up with a lot of examples of it, but it can exist as a natural selection pattern.3479

Next one, stabilizing selection is the opposite of what I just had showed you.3487

It is favoring the middle range.3494

Let us do that in green.3502

Stabilizing selection would be like this.3508

I will give you two examples.3514

The wing size of birds, imagine birds trying to be effective in moving when there is a storm.3518

Wings that are way too big, may catch a lot more wind and just be really hard for the bird to fly effectively.3525

Wings that are really small, you can imagine why that is a problem.3534

Having this medium sized wing may have been selected for at a certain point.3537

A species has a particular length wing that is more in the medium range.3542

Another one could be the body size of a lizard.3547

You can imagine that being a really tiny lizard has its advantages because it is easier to hide but moving really fast,3552

when you have tiny legs and a smaller body, you are not going to be able to make as much of a distance when you are moving as fast as you can.3560

They can be selected against, a very large lizard of that same species can move faster but hiding all of its body might have been a problem.3569

Maybe its tail sticks out and its tail does not come off when it gets eaten or its little foot sticks out and gets eaten.3579

Having that medium body size is the happy medium, in terms of like being able to hide easily and being fast enough.3587

That is stabilizing selection.3593

Artificial selection is a little bit different.3595

This is when humans are selecting for traits.3598

Humans select, this is not natural selection, it is the exact opposite of that.3603

It is not natural at all, because we are determining what we want and we are influencing the breeding patterns.3610

This has been done so many times with agriculture, plants, dogs, cats, horses.3616

Purebred dogs from different parts of the world, they have an inbred.3625

They have been selected for, to get that certain characteristic.3631

They would be no Chihuahua, there would be no Great Dane without human interference.3635

Thousands and thousands years ago, they were taken out of the wild.3641

We still do not know how old - it could be way before 30,000 years ago, as far as we know.3646

Wolves were taken out of the wild, wild dogs were taken out of the wild, bred together.3657

Certain members were taken, like if they wanted a small dog, they took the smallest members of the litter and mated them,3662

took the smallest member and kept giving that pattern.3670

It has lead to all these different dog breeds that are still the same species but have very different looks,3673

because humans have selected for those traits.3679

Some of the dogs had purposes, like in terms of hunting or being a dog that could catch rodents,3683

or just being a lap dog, just being a dog that you wanted to have around the house and pet.3690

Artificial selection has also been done with crops.3695

The head of lettuce probably would have never existed in the wild.3698

A head of lettuce and some other vegetables that came from this wild plant where the leaves did not look like that.3702

We selected for the offspring of a plant from thousand years ago that had greater leaves.3711

Now, you get to the point where lettuce is just this bundle of leaves altogether.3716

Broccoli is a bundle of the florets.3721

Definitely, we have influenced crops over time by selecting for certain looks and manipulating the breeding patterns.3726

Sexual selection, this is still natural.3733

Sexual selection explains how you get certain characteristics in males and certain characteristics in females.3735

I’m going to get to that more later on in this lesson, about how that actually affects a species over time.3742

Sexual selection is the reason why you see antlers on deer or moose.3750

The reason why you see certain color patterns or songbirds have pressure to have a very unique song, a beautiful song, to woo a female.3755

Sexual selection, it definitely is something that makes it where, if you cannot cut it,3766

having this male characteristic or female characteristic, you are probably not going to be chosen,3773

you are probably not going to have offspring.3778

More on sexual selection, sexual section is fueled by mating decisions, selecting for I want to mate with you.3782

Sexual dimorphism means that there are two forms.3792

It is where sexual selection so that it is really easy from our point of view to tell apart a male or a female in the wild.3796

When we do not have to look at their genitals or look at their internal anatomy.3803

A good example of that are gorillas, they have profound sexual dimorphism, meaning, di two forms.3806

Male gorillas are like twice as massive as the average adult female, much more musculature.3815

Part of it is just how they mate, the male can just take the female by force, if he wants.3824

There are other examples where there is not profound sexual dimorphism.3830

Compared to a lot of other primates, humans do not have a great deal of dimorphism.3833

Yes, males on average are taller, males on average weigh more.3839

There are differences in the hair on a male’s body and female body.3844

That has a lot to do with testosterone.3849

But compared to other organisms like gorillas, the dimorphism is not as profound.3851

What that is attributed to is, there is a lot more pair bonding between males and females.3857

We do have a lot more in common and we tend to hang around with each other more,3863

and have examples where humans mate for life.3867

Whether or not that is natural is up for debate but.3871

It is deftly mating for life and having one partner is much more common in humans than in other primates.3876

The more sexual dimorphism, the more the males and females look very different.3883

Examples, antlers in stags, stags are male deer.3890

Early on in evolution, having a little projection from the skull like hardness here, we are talking before antlers officially occurred.3895

If males at that point would like bat heads trying to be more dominant.3907

Having a little projection, it can easily win so then the women or the female deer would have been, I’m going to choose you3914

because you just kicked all those deer butts, you butted their heads and they had no chance.3926

And then, they pass on that little projection to their offspring.3936

Few generations later, mutations makes that projection little bit higher.3941

You can see that over time, if you extrapolate that pattern, you can end up getting really large antlers.3944

The pressure of antlers is so great that if you are born without them, good luck.3951

Large female frogs, in most frog species, the females are larger than males and that allows them to have a lot more eggs in their ovaries.3955

And also, they can carry them around in their back because when they mate, the male hops on the female back,3965

they go to a private spot and do the little honeymoon.3971

That is where the male and female release their eggs into the water, that is most of them do it.3975

Large female frogs were definitely selected for.3981

The males tend to go after the larger females.3984

Large male gorillas, I mentioned that in the previous slide, they can defend their troop much better.3988

They definitely, the larger the male gorilla, the more dominant he can be, in terms of getting females.3997

Song complex, the male songbirds, this has been studied so many times by scientists.4003

There is pressure for male songbirds to come up with a unique complex song that is more complex than the male neighbor.4008

If you come up with a really novel, very different song that catches the females attention, you are more likely to have offspring.4016

A male songbird that cannot come up with a unique song, might not mate at all.4024

And then, the genes will fade away with that particular bird, if they cannot pass on those genes to offspring.4028

Display in male blue footed boobies, this is a blue footed booby, you can find them on the Galapagos islands.4037

That is not colorized but that is an actual color, no color has been added to this photo.4043

That is really what their feet look like, that is the blue footed booby.4049

If you are wondering about the booby thing, why they call it that?4053

I know that is a slang term for breast.4056

But booby to the British part of English language means like dummy, like you are being a booby, it is a nickname for dummy.4058

Whoever named them thought they were not the most intelligent birds.4069

The reason why there is that blue footedness is because they do a little dance, they do a little display to show their feet.4074

The ones that have the more colorful feet, they get more ladies, they end up mating more.4081

Maybe in the future, there will be even more interesting colors.4088

It all comes down to, if they get mutations and if they can pass those on.4092

Natural selection acts upon those phenotypes, those looks in the animal or organism based on what is happening in their genes.4097

In humans, there is definitely sexual selection.4106

I will not comment much about that because it really depends on the person.4109

Some people really value intelligence.4113

Other people really care a lot about physical appearance.4117

I think a lot of people want a bunch of things in their ideal mate.4121

But, whatever it is that trends, in terms of what people want in a partner,4126

what they say they want in a partner in our species, it comes down on human evolution.4131

If people are not attracted to intelligence or humor, it is safe to say that those things were selected for early on in our evolution.4135

Humor shows that you got some good brains, if you can come up with that funny thing or comment about a situation.4145

Intelligence, you are probably going to come up with novel ways4152

to figure out how your family can survive or how you can resist some kind of hardship.4155

If you are strong and big, then you are probably a healthy individual who can resist dying from an illness or getting beat by a predator.4162

There are reasons why humans select for traits, even apart from societal factors.4173

Notes on natural selections, more details in the way natural selection works.4184

I told you I will show you the slide with the large proboscis from this moth, incredible how long that is.4187

When it comes out of its mouth, it is longer than the length of its body, that is insane, it is amazing.4193

The environment selects for a phenotype.4202

I mentioned this on the previous slide.4204

The environment cannot tell whether or not you are heterozygous or homozygous.4205

The environment just selects for what you got going on with your abilities in your body and what you are able to do.4209

Phenotype is the physical manifestation of what is going with your genes.4217

This is why harmful alleles can be maintained in a population.4225

Because if the homozygous dominant individual and the heterozygous have the same exact phenotype, they both will be just successful.4229

Two heterozygous getting together can have offspring that that homozygous recessive genotype.4236

If this codes for something problematic, they may not survive very long at all.4243

They will still keep being born, if you have individuals getting together with this and this.4248

If this is confusing, you just look at the genetics lesson, that came prior to this.4254

Natural selection can amplify or diminish only heritable traits.4262

This comes back to that acquired characteristics are not passed on.4265

It can make you more likely to be successful having offspring or having a lot of offspring, or more successful in getting mates.4269

But, only what is in the sperm or egg is going to be passed on.4277

A trait that is favorable in one environment, maybe disadvantageous to another.4282

I mentioned this earlier with, if a snowy environment because of a heating on earth4285

becomes a very non snowy environment, all of that white look, white fur or white skin will not be very good.4291

Mutations are the fuel for natural selection, that is what causes changes in proteins4299

that will cause changes in organisms appearance, in their abilities and what they can do.4305

Mutations, oftentimes are a bad thing but when that change in DNA results in a positive change,4311

that is what fuels evolution.4318

Reproductive isolation, what this is about is more reasons about how species can develop.4321

How does one group end up becoming too different species overtime, how does it happen?4329

One of the main reasons is reproductive isolation.4334

What is it that causes parts of this group to not be able to reproduce.4337

What makes one species, a single species, is a group of organisms in one area4342

that can successfully make offspring with one another, because same chromosome, same types of genes.4348

If you get to the point where they can no longer make offspring that is called prezygotic reproductive isolation.4355

Prezygotic meaning something is preventing sperm and egg from getting together.4361

The zygote is the product of fertilization, sperm and egg combined.4366

There are various ways that can cause portions of the population to be unable to produce offspring and remain that same species.4373

One of them is temporal isolation, temporal meaning the timing.4379

Temporal isolation, a good example is frog species.4383

When we look at, sometimes it is like 50 or more frog species in one area, let us say it is in the rainforest.4387

Frog species in an area, one of the reasons they may have become different species of frog is the time, the year they desire to mate.4395

When we look at frog species in an area, sometimes you will have species that mate in April,4406

other species mate in May, other species late May, other species early June.4410

There is not an overlap of all of their mating periods.4415

Temporal isolation meaning if way back when, some parts of the population, feel it in April, other ones feel it in May.4419

If you keep having that happen, you will get to the point where this group and all their ancestors and descendants,4428

they just do not want to mate in May, and vice versa with these.4435

Even if you got to the point a million years later where they decide mating at the same time,4438

mutations have affected their populations differently to the point where they can no longer have sperm and egg being compatible.4443

They are released in the water and the sperm and egg just would not get together4450

because of differences in genes that have developed over time.4454

Behavioral isolation, this could be an insect that has a certain kind of thing it does to attract a mate4457

or it could be something like blue footed boobies.4469

Maybe early on, maybe there could have been that particular bird with a different colored foot4473

but they did a dance that was very different than the ones that end up being blue footed boobies.4483

Behavioral differences can make it where all these other ones got together4489

because of a different kind of mating dance than these, but the other ones that we do not see anymore they are now extinct.4494

There could have been yellow footed boobies or there could have been green footed boobies.4501

I do not have any proof of that but it is a possibility.4507

That is behavior isolation.4511

Mechanical isolation, this one is interesting.4513

The mechanics of them actually mating is not compatible.4517

Like I said, all dog breeds are the same species still.4522

I have heard canis familiaris has the form of domesticated dog, as their scientific name.4527

Even though a Chihuahua and a great dane are the same species,4537

the likelihood of a great Dane and a Chihuahua is successfully mating is very low.4541

The one is way too big for the other one, for them to actually have intercourse.4547

If they were never able to make offspring over like, let us say another thousand years, if they are still around at that point.4553

Even if we took sperm to one and egg from the other, after all that length of time and try combine them in a lab,4560

it is possible that the sperm and egg just would not be compatible.4565

We cannot even make a successful zygote because so much time has passed with them being unable to make offspring,4568

that mechanical isolation has made it to where they are now officially different dogs species.4574

Gametic isolation, they are still able to have sex but something is preventing the sperm and egg from actually mixing.4581

Something is not allowing them to come together.4592

It could be that something is structurally different about the sperm, that is making it unable to get into the egg, that could be.4596

It is gametic isolation, because gametes are sperm and egg.4607

Geographic isolation, that is this example here.4611

Here I have a sea snake, all snakes need to breathe air, they need to go up and actually get air,4616

but sea snakes can go on the water for lengthy periods of time.4622

One of the theories about why there are land snakes versus sea snakes now is, at a certain point we think they were all land snakes.4627

But, the choice of some of them to hang out more in the water and others to stay on land,4635

maybe based on food availability, and a sense of adventure when some of them go into the water.4641

That geographic separation could made it to where at this point, if a sea snake comes out of the water4650

and tries to get together with a similar species of land snake, they have been isolated in two different geographies,4660

two different places for so long that now they can no longer get together and speciation has occurred.4668

Another example of geographic isolation, there is a certain squirrel or chipmunk, I think it is a squirrel.4674

In the Grand Canyon, that got separated because of the Colorado river4682

going through the Grand Canyon for millions of years, carved that amazing canyon.4687

Way back when, there was one population of that rodent that was interbreeding.4691

It got separated by the Canyon.4697

They have been separated for so long, they are completely different species.4699

Now, even if we took their sperm and egg, and allow them to try to mix them and make an embryo, it would not work out.4703

That is another example of geographic isolation.4709

These are all prezygotic factors that made it so that sperm and egg just are not getting together.4711

This is reproductive isolation that is post-zygotic, meaning the animals and the plants here can actually make a zygote.4719

But something happens at that point that is going to make it where the chance of them remaining the same species over time is low.4728

Hybrid sterility, the example here is the mule.4737

Here is a mule, horse, and donkey give you a mule.4743

But a mule is sterile, it cannot have babies.4754

This is preventing the horse and donkey from like being the same species.4759

If you cannot make offspring together, over time the amount of mutations that happen with this group4764

and the amount of mutations that this group are going to be completely different mutations.4773

Their genes are going to be changed so much, that maybe one day even their sperm and egg will no longer be able to get together.4776

That is possible, and eventually, the making of a mule may not be possible.4783

This is known as hybrid sterility, if your hybrid, your offspring is consistently sterile because of a weird chromosome number.4788

That results from the different chromosomes here in the meiosis equaling an odd number which ends up happening in the mule.4796

You are going to have that reproductive isolation that is post-zygotic.4804

Hybrid inviability, sometimes that just means that the hybrid is less healthy.4808

The hybrid of these two organisms just comes out not very fit, likelihood of it surviving to be reproductive age is not going to work out.4816

That is the inviable nature of the hybrid.4827

Hybrid breakdown means, maybe in the generation of making the hybrid, having the sperm and egg coming together,4831

making the zygote, maybe that second generation works out okay.4838

But when those hybrids make offspring, it just gets worse and worse.4842

That is the gradual breakdown, it is something about the chromosomes fitting together,4847

the genetics working in that subsequent generation is causing breakdown of that lineage.4852

Speciation, in addition to those reproductive isolations, those kinds of things, you can have ways where organism separates.4863

This is the process in which a new species forms from an ancestral form from a single group.4873

Several factors can lead to development of species besides reproductive isolation.4878

Nonrandom mating that means sexual selection.4884

Random mating is you can mate with anybody and it does not really matter.4887

Nonrandom mating means they are choosing or selecting for a particular traits.4893

Over time, that encourages those traits to remain.4897

If you do not got those traits, you are probably not going to have much offspring.4900

Mutations, I told you before that, mutation is the raw material for natural selection to act upon and for evolution to occur.4905

These two things go hand in hand.4914

Small populations, this relates to the island phenomenon.4917

When we look at island biology, you get this really interesting endemic forms, giant species, dwarf species.4921

The smaller the population, the less sort of mixing of various gene forms you have.4931

Mutations can be kind of exaggerated more quickly over time in a smaller population.4937

Immigration and emigration, also having new organisms come in or organisms leave,4943

can affect the average genetics you have in a population.4948

Imagine that you have a population where they are all a certain color and you have this group over here that is a little bit darker.4954

You can have organism go over here and interaction with them could create this medium colored group.4963

Over time, they do not mate with these because they have a different color, and they are in a different area.4972

That particular introduction of a new individual that immigration can impact the species.4977

Emigration would be the leaving, if you have emigrate, you leave the population.4982

Speaking of leaving the population, this is a fossil for homo floresiensis.4988

This is the scientific name for a relative of ours, not the same species, a relative though, that is found in the island of Flores.5001

It is pre much known as the hobbit species for human ancestors and their relatives.5010

The skull size is remarkably small, it is hard to tell because I do not have another skull near it.5018

If the human skull is this big, this skull is about that big.5023

Their average height as an adult is 1 meter, a little over 3 feet, that was the average height.5026

We think that either they came from a group of early home erectus or there is other theories.5034

Let us say a group of early, even later homo erectus individuals got on a boat,5039

a primitive kind of raft, canoe, whatever it might be, and went to the island of Flores.5047

They were isolated for so long and certain environmental factors, nutritional effects, mutations,5051

made it were on average they were much shorter.5059

They end up being two completely different species.5062

Adaptive radiation, this is the radiating of various new species that can be linked to a singular ancestral species.5067

The radiation here is not UV or X-rays, or something like that, we mean radiating.5074

Think about a circle with a radius, kind of moving out from the center.5081

Adaptive meaning as time goes on, these different groups radiating out adapt in different ways because of different environments.5086

Slight changes in their appearance can be linked to natural selection in their habitats.5095

Since the habitats of these descendants, the species that descend from the common one.5100

Since the habitats are slightly different from each other, you get slight differences in the descendants.5105

Examples, Darwinian finches on the Galapagos and silversword Hawaii, here is the finches.5114

Darwin sketched these images.5122

You can see that they have the scientific names here.5126

The Galapagos archipelago, there are numerous islands.5131

These finches are in various islands.5135

They all came from a common ancestor on the mainland of South America.5137

Way back when, all it took was at least two of them to leave South America and land on one of the islands,5142

these volcanic islands that popped up.5149

They had offspring, as time went on and the finches went to different areas, different food sources,5152

and different habitats, selected for different traits.5160

Number 1, really good at cracking nuts and hard seeds because its beak is fitted to that.5163

This one not as good at that, it has a more narrow beak, probably better at eating worms5169

or fitting its beak into a little hole in the trunk of the tree to get insects.5175

Different finches with different beak sizes and shapes, matched a different food sources.5181

I want you to think it is as simple as like, let us say two of the number two finch,5188

a male and female have offspring and all of a sudden it looks like number 4.5195

It is not going to be that dramatic.5199

We are talking baby steps in beak size over millions of years that make over 30 finch species.5200

There is a lot of them in the Galapagos.5210

The silversword of Hawaii comes from the sunflower family that we can find in North America.5213

All it took was a seed or two, drifting from the mainland of North America, all the way over to the volcanic islands of Hawaii.5219

When you look at the silversword, genetic evidence has shown that they all are related but5230

their look is very different in different terrains, different elevations, different soils.5237

Some of them look more like a bush, some of them look more like a yucca plant.5244

The silversword is another example of adaptive radiation.5250

Next we have the Hardy-Weinberg theorem.5257

This is a hypothetical model that was conceived from when evolution is not occurring in a population.5259

It is rare that evolution is absolutely not occurring overtime in a population because natural selection, mutations,5267

those things encourage changes over time.5274

This was conceived as a hypothetical model, just for the sake of comparison.5278

You can see on whether or not for particular genes that natural selection is acting upon them.5282

It is something that can be very valuable when you look at a natural population, whether it is animals, plants, etc.5289

When a population is in Hardy-Weinberg equilibrium, the equilibrium means that things are remaining the same, that evolution is not occurring.5296

When that is happening, the following five conditions are true.5305

All of these things have to be true for this equilibrium to be happening.5310

Number 1, no new mutations, to have no new mutations at all, meaning the DNA is staying the same overtime,5314

the alleles that were there to begin with, nothing has been changed.5322

There is now new allele developing, that is rare.5325

Random mating that means no sexual selection because remember, a sexual selection or nonrandom mating,5329

they are picking particular things that are true about males or females.5334

Since those are favored, certain things about those characteristics can be exaggerated and favor it even more over time.5340

That tends to change species.5346

Mating has to be random.5348

No natural selection, for natural selection not be happening at all, that is rare.5350

Nature selects for a favorable characteristic, the ones that do not have those characteristics,5355

they are not going to live as long, they are not going to have as many offspring.5360

Large population, some populations are really small.5363

Like I told you with islands and isolated areas having these much smaller populations,5366

you can get more exaggerated evolutionary changes in shorter periods of time.5371

It has to be a large population.5377

No immigration and emigration, no new organisms of that species is coming in the population and5380

organisms not leaving, that will change the allelic frequencies.5386

I will tell you more about allelic frequencies later on in this slide.5390

Let me give you of something in humans where Hardy- Weinberg is actually pretty valuable.5394

I’m going to erase these check marks because we are going to recheck these five things, to see if they are true.5400

With something like PKU are genetically inherited disorder which stands for phenylketunuria.5406

Phenylketunuria, this makes it so that the person who has inherited and they inherited it because of homozygous recessive.5420

You can also have this or this, you are a carrier.5428

If you have a homozygous recessive form for that gene, you cannot break down phenylalanine.5432

Overtime that can cause problems, if you are introduced to phenylalanine.5437

Like I told you before with the genetics lesson, the beauty of this is, if your child is born with it,5443

it is diagnosed and you knew you child has it, just do not feed them phenylalanine ever.5449

You are good to go, you will not get the symptoms of the negative sides of phenylketunuria.5454

You can apply the Hardy-Weinberg equilibrium to this because, let us assume that there are not any new mutations.5460

Let us say we are taken to a population of the United States, the global population will be too much to talk about.5468

Let us take the population of the United States, humans there, in relation to this.5474

No new mutations mean that, there is just a dominant allele and the recessive allele.5479

There is no mutations that are occurring and being passed on.5485

There are not two forms of a dominant allele or two forms of recessive.5487

We can assume that, those alleles are being passed on and that is it.5493

No new mutations.5497

Random mating, humans do not typically choose mates at random, for having children.5499

We tend to be pretty picky about who you want to make other humans with.5505

There are good reasons for that.5508

In terms of this particular gene, because Hardy-Weinberg has to do with one gene and one population over time.5510

In terms of PKU, there is random mating because you cannot look at someone and be like,5518

he is not a carrier for PKU, you cannot.5525

You cannot tell whether or not someone is a carrier.5529

Because of that, it is random mating in a sense, related to this gene.5532

No natural selection, with a lot of other things in our species, nature favors them or it does not.5538

In relation to this, there is a natural selection because when you are born homozygous dominant,5546

you are fine, you can breakdown phenylalanine.5551

When you are born as a carrier, there are no symptoms, you have the dominant allele, you are fine.5553

No natural selection against that.5559

There is no natural selection against these people because, now that we can diagnose it,5561

especially in this country, we know the ways to avoid the problems.5565

We know, do not eat that, it is fine.5571

We can say that, even if you are homozygous recessive, even if you are born with the disorder,5575

you are not being selected against.5580

There is no mechanism encouraging the recessive allele to go away because that would definitely cause evolution over time.5583

Large population, in the United States, there is over 300,000,000 people, that is large.5592

No immigration and emigration, of course people immigrate in this country, people emigrate out, people leave.5597

But it is probably not affecting this particularly.5606

Worldwide, you can find this recessive allele and dominant alleles.5614

There is no way to know if people coming in this country or leaving this country are actually affecting this.5619

We can claim that these five conditions are true related to PKU.5629

The equations, this is where the mathematics gets involved.5634

P + Q =1, what was that mean?5639

I'm not going to use this P because I do not want to confuse you what this particular P means.5641

This P means the frequency of the dominant allele for a gene.5647

The Q means the frequency of the recessive.5651

The 1 means 100%.5653

Let us take gene A, we are talking about, let us say sickle cell anemia.5655

P equals the frequency of A, has a dominant allele.5660

Q equals the frequency of a.5668

1 is the total, that is the total number of the percentages of alleles all together.5673

This P could be 0.7, this one could be 0.3, of course that equals 1.5681

This is telling you that, this will be strange in the United States because the frequency of the recessive will actually be much lower.5687

The number of carriers of sickle cell anemia is not that high.5694

The number of people born with it is not that high.5697

Let us say for some, this means if you look at all the people who have these genes,5700

70% of the alleles are dominant and 30% are recessive.5706

If that was true, we can plug those things into here.5710

It is P squared meaning like two dominant alleles, homozygous dominant, + 2 PQ,5716

the heterozygous condition, + that squared homozygous recessive, that is all the possibilities.5722

If we plug this into there, it would be 0.7 squared + 2 × 0.3 + 0.3 squared =1.5730

What happens here, we get 0.49 + 2 × 0.21, I should do 0 to keep it consistent.5758

0.42 + 0.09 =1.5770

If we add all those up, it actually does equal 1.5781

This is showing you that there is equilibrium with that.5787

As time goes on, it is less likely though that you are going to have that Hardy-Weinberg equilibrium.5790

For there to be no new mutations, completely random mating, no natural selection, a consistent large population5797

and no significant immigration and emigration, it is rare that all of these are true.5804

Like I said, this is a hypothetical model that allows you to observe how quickly or how rapidly evolution is taking place with population.5808

Microevolution, this is the short term evolution of species over time.5820

These are the baby steps that over time, you get big evolutionary changes.5825

Natural selection is going to be influencing that.5830

The environment changes over time, the environment is never completely consistent over time.5834

The earth goes two cycles regarding amount of gases in the atmosphere, temperature changes, rainfall changes.5839

The diseases in the environment, viruses in the environment, there is a lot of changes over time.5848

Genetic drift, it means that you can have a drift in the genes meaning the forms of genes overtime,5853

can change dramatically because of circumstances.5862

A bottleneck would mean, let us say this is a population of all the individuals of the species.5866

The red square means they have a certain look or a certain characteristic.5872

The blue is the other characteristic.5877

It is like two forms in a population.5879

Bottleneck means like, if we had this bottle and made a very narrow exit point, this could be like a crazy natural disaster that occurred.5881

Flooding, earthquakes, famine, disease, whatever, that just eliminates over 90% of them.5891

The ones that come out, let us say the ones that come out are three blue dots.5901

All the red squares die.5908

It is just coincidence, the natural disaster was not selecting for anything.5910

It just killed a lot of them, you are lucky to survive if you did.5915

This is an example how a genetic drift can completely alter a species in a very short amount of time.5919

We have eliminated the alleles that were in these red square, their genes are gone, they are dead.5925

All that is left is this, that can alter species in a very short amount of time.5935

The founder effect is similar, the founder effect means, I’m going to erase this square around them because they are going to be moving.5940

The founder effect is related to this.5953

This original population, some of them move there, some of them move there.5960

It was purely coincidental who moved where.5966

It turned out that no blue dots are here, no red squares are there.5970

There is a little mix over here.5974

The founder effect means this group, they colonize, they will go to a new place.5976

Whoever is there and starting a new population, their alleles, their gene form will determine5981

whatever happens next because, there is no alleles from here in this situation, and vice versa.5986

This could explain why is it that certain groups, certain racial groups in the human species,5993

tend to have higher percentage of disorders than others.6003

I read recently that with Tay Sachs disease, it is not just the Afghan and the Jewish population that has a high instance of carriers.6008

Interesting enough, the Irish people who are pure-bred Irish, they actually have a higher incidence as well.6017

Why is that, it just turns out that certain people in early human migrations had mutations.6026

It dependent on how many of them end up migrating to one area or another.6035

Some of it can become completely coincidental, that you had just a little bit more of these alleles in one place than another.6039

When it comes to migrations of all kinds of animals, it certainly has an impact the founder effect.6047

Gene flow is the flow in and out of the population.6053

Emigration or immigration can impact the amount of alleles for a certain trait, increasing or decreasing over time.6057

Nonrandom mating, I bought this up a few times in this lesson.6066

Picking a certain characteristics in offspring, those things can get exaggerated fairly quickly.6070

Mutations will be encouraged to happen in relation to one kind of characteristic that can contribute to of microevolution.6077

Clarifications about evolution, these are misconceptions that people might have.6086

I want to make sure leaving this lesson that, that you do not have them.6090

A single organism, for example you or me, cannot evolve.6094

We are born homo sapiens, we will pass on as home sapiens.6099

If you are wondering, if a single organism cannot evolve, then how does evolution happen?6105

The smallest population that can evolve is a population.6109

The smallest group that can evolve a single population of organisms, of single species.6113

Then getting isolated from another group, certain mutations happening with them,6119

certain kinds of natural selection happening with them is different from others, that will encourage evolution to happen.6125

It is gradual things that eventually one of them is born with so many significant differences from the ancestral species, they can no longer mate.6130

That is really those steps needed to happen for speciation to occur.6140

But a single organism cannot evolve.6145

We will contribute if we have children to the genetic lineage of the species overtime.6149

You know, apart from genetic transformation, you are not going to change your species.6157

Genetic transformation is unlikely in an adult human because to go in and put different genes in all of our cells,6163

at this point in time is not possible to do it successfully.6175

In the future, who knows.6179

There is not a single missing link with human evolution.6182

The next lesson is called human evolution in this course.6184

I recommend you watch it.6188

But there is not a single missing link, people has this misconception.6190

I think if we find that one thing, that one fossil, we will know evolution is true.6194

Think of evolution as a giant puzzle on the wall.6200

We can see the big picture when we look at the puzzle and you can tell what is going on.6204

But there are missing pieces all over the puzzle.6209

Every time a new fossil is discovered, a piece gets filled in that makes the lineage over time much more obvious and much more apparent to us.6213

Certain thing that is a little bit fuzzy in the picture become more clear.6222

There is not a single missing link.6226

In the human evolution lesson I mentioned, you will see that we do have a sense of where we came from.6228

Ancestors, cousins of ours that went extinct and did not have offspring.6234

It is kind of dead ends in the branch of the tree of evolution.6240

It takes a long time for evolution to occur, a long time.6243

I have heard that the minimum, this is estimated, the minimum amount of time has passed6248

to have a significant evolution change our species is 50,000 years.6252

50,000 years, that exceeds all of written history.6256

It is tough to imagine that but it makes sense.6264

To get enough mutations and enough natural selection overtime, to have significant changes, yes a lot of time has to go by.6266

However, with certain individuals, certain kinds of species, it can be observed in action.6273

Bacteria have such a fast generation turnover, we can see evolution happening before our eyes,6281

in a single lifetime of a human.6288

Here is what I mean, there are research done in a certain species of bacteria.6290

The original species, the original population of bacteria, half of them were kept growing and6296

the other half were frozen, they are kept dormant back in the 1980’s.6302

This other group of the same species, they let grow and grow.6308

Over about two decades of time, they kept making offspring and they would transfer them to a new plate, new petri dish.6312

They kept making offspring.6319

Then, about two decades later, they took samples from the descendants of the original.6322

They unfroze these and compared them.6328

What happen, because we just let them grow, we have not specifically targeted and made changes in their genome,6331

turns out that the new ones, 20 years later, naturally were dividing faster than the originals.6339

They had gained some kind of mutation that made the pace of cell division much faster.6346

That happened just because of raw mutations.6351

That is proof that you can have natural mechanisms that fuel evolution.6353

It is amazing that you can really see evolution happen in an organism that reproduces as such a quick rate.6358

Some bacteria can reproduce in as little as 20 minutes.6367

Humans did not evolve from chimpanzees.6370

No, we did not come from them.6373

They are distinct distant cousins, but of all the species that exist today, they are our closest living relative.6375

Bonobo, specifically.6383

There are a lot of other ones that more closer to us.6386

You will read about those in human evolution lesson, but they are extinct now.6391

Even though chimpanzees are our closes living relative,6396

they were at least 20 other more closely related species, ancestors, and cousins of ours, that are now extinct.6399

Here is a picture of bonobo chimpanzee, remarkable kind of human look to their face.6408

They do have plenty of differences of course.6414

All primates do have a common ancestor, that you will read about in that human evolution lesson.6419

We all have branched off of that because of natural selection, mutations, reproductive, isolation, etc,. You had speciation occur.6424

I hope you enjoyed this lesson, thank you for watching www.educator.com.6436

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