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  • Hi. It's Mr. Andersen and welcome to Biology Essentials video number 4. This

  • is on Scientific Evidence for Evolution. Here is a picture of Charles Darwin much later

  • in life. Charles Darwin was a very meticulous scientist. He gathered copious amounts of

  • data and to show that evolution was true and that his mechanism of natural selection was

  • right. Unfortunately he did not have a real good understanding of genetics and DNA obviously

  • was not around back then, but the scientific evidence for evolution right now is pretty

  • overwhelming. Some of the things he could have pointed to were fossil records. This

  • is a baleen whale. If you look at the fin of a baleen whale it almost looks exactly

  • like the bone structure in the human arm, which suggests that both I and the whale have

  • a common ancestor that had bone structure similar like that. Or you could look at the

  • rear legs. Why would a whale have rear legs unless at one point it actually walked on

  • land and evolved from something like that. And so today what I am going to talk about

  • is evidence for evolution. So what is evolution again? It's just changes in the gene pool.

  • But specifically here we're not only talking about microevolution but macroevolution as

  • well. First I'm going to talk about three things that were available to Darwin, and

  • he talked about. Number one is Biogeography, in other words where living things are found.

  • I'll talk specifically about the Galapagos Tortoises. Next he talked about fossils. An

  • example I'll give you is horse evolution over time. Next, homologies or those are characteristics

  • organisms have that show common ancestry. I'll talk about both homologous structures

  • and vestigial structures. And then I am going to talk on a few things that Darwin didn't

  • have available to him. Mainly molecular evidence - DNA is the trump card when it comes to evidence

  • as far as evolution goes. And finally I am going to show you how we can use mathematical

  • models to support our models for how evolution actually takes place. So we've got a lot to

  • do so I better get started. Let's start with where Darwin started, on the Galapagos formulating

  • his ideas. And I have been here as well. And to see these tortoises the first time is pretty

  • amazing. Darwin's idea was that the giant tortoises on the Galapagos had moved from

  • here out to the Galapagos. And so it had to float there, make it someway from the mainland

  • to the Galapagos. And when he looked at the tortoise in Ecuador it looks very similar.

  • There's no predators and so they are able to get very, very big. You can see there

  • are clear differences in the size of the tortoises and more in their structure of their shell.

  • Tortoises that come from really barren areas actually have a longer neck and what's called

  • a saddle shape versus a dome shape. This is one from the highlands of Santa Cruz and this

  • one is from San Cristobal. Now why do we just find tortoises there? Well there was a founding

  • population that actually moved there. Now before Darwin most scientists at that time

  • believed in special creation, that God had placed everything specifically on the island

  • where it was. And Darwin, when he went to the Galapagos and started to see these islands

  • and the similarities but also differences between those he started to realize that life

  • and where life is found, we call that biogeography, is big evidence for evolution. Example, South

  • America used to be connected to Australia. And we had a certain type of mammal there

  • called marsupial mammals. We had eutherian mammals up here on the top. And when those

  • two came together there was a war of the mammals. And eutherians really did fairly well and

  • wiped out a lot of the marsupials that were there. But Australia, as it remained adrift

  • kept those marsupials there. So it would be another example of biogeography. Next we could

  • look at the fossils. It's surprising how much fossil evidence we actually have, because

  • it's hard to create a fossil. The geologic properties required for that are pretty tough.

  • A great example would be in horse evolution. Through time horses have gotten larger and

  • larger and larger as their environment has changed and they move from more of a browsing

  • to more of a grazing kind of animal. But we can see that growth reflected in the change

  • in the fossil record. In other words the teeth become flatter. They have to run faster when

  • they're out on the plains. And so they move from many digits to just one digit. And so

  • we can see this transition. It's not linear, it's branched. In other words if we look at

  • horse evolution there are many dead ends, there are many branch points. But we can see

  • that there is a continuous thread all the way from those first horses to the horses

  • that we have today. So horse evidence, fossil evidence is really good. There's a surprising

  • amount of data on whale and whale evolution if you are interested in that you can take

  • a look. Next is, and Darwin talked about this as well. In fact he actually mentioned this

  • and I've got a big one of these. This is called a Darwin's tubercle, which is like a little,

  • I do not know if you can see that, where your ear is and what it suggests is that we share

  • ancestry with other primates who have this bump there as well. Homology or homologous

  • means that they come from the same ancestry. And so this would be a human arm, this would

  • be a dog leg, this would be a pigeon wing and this would be a fin of a whale. And if

  • you look at it you could definitely if you are an engineer design a wing more efficiently

  • then this wing right here but natural selection started with an organism that had the same

  • bone structure and so it's used that bone structure and it's manipulated it to make

  • the appendage that we have today. Vestigial structures are another thing that I could

  • talk about briefly. Vestigial structures are structures that once had and did something

  • but don't do anything anymore. An example would be goosebumps. I get goosebumps when

  • I get scared or when I get cold, but I don't have a lot of fur, so it doesn't make me large

  • and it doesn't give me much insulation. Wisdom teeth, a primitive tail, all those things

  • are vestigial structures, an appendix, and they point to an ancestor that actually used

  • those but has lost them over time. And so anatomy gives us huge pieces of evidence for

  • evolution. But the one thing that Darwin didn't have was DNA. And so the best way to talk

  • about DNA to start is to talk about the telephone game. If you've ever played the telephone

  • game, essentially what you do is you start with a phrase, let's say, "the fat cat ate

  • the rat". And then this phrase is going to be whispered to the second person in line,

  • who will whisper it to the third person in line. But let's say the third person in line

  • here, we'll call this person yellow, makes a mistake. Instead of saying "the fact cate

  • ate the rat", said "the fat car at the rat". Now that's message, that's the DNA. And so

  • when that DNA is copied again, that mutation is copied on as well. So "the fat car ate

  • the rat". So that goes over here to pink. Pink does a nice job of passing it on but

  • then eventually we get another mutation here. So we get a red mutation. And now it's "the

  • fat car ate the bat" And now "the fat car ate the bat" and finally "the far car ate

  • the bat". So when we get to the end the DNA is very similar but it's changed a little

  • bit. And each of these are a mutation. We could call that the yellow mutation, the red

  • mutation and then the purple mutation. And so life started with one strand of DNA. And

  • all living things on our planet have that same DNA but these mutations have accumulated over

  • time and so they tell us a lot about who's related to whom. In other words if you were

  • to just tell me what the message is and you had this mutation here in yellow but you didn't

  • have the red one, I could kind of place where you are and who you were standing next to.

  • And so if Darwin had evidence related to DNA it would have been a lot, he would have had

  • a better, an easier job convincing other people that he's right. So let's talk about some

  • specific DNA evidence. An example I am going to give you here is the Human FGF2 gene. Over

  • the last 10 years we have started sequencing huge genomes. And a genome, remember is the

  • sequence of all the DNA inside that one living organism. The one I am going to look at is

  • one that makes fibroblasts, so it's helpful in healing of wounds. And so we are going

  • to go to this website (http://uswest.ensembl.org/index.html) right here and we're going to take a look at,

  • let's go right here, we're going to take a look at this gene. So this is the human gene,

  • FGF2. It's found on chromosome 4 and you can tell like how many base pairs, it's 6000 letters

  • long. It tells me where exactly it is. We've learned so much. We could actually look at

  • all the letters in that gene. Each of these red ones here would be an axon, so not really

  • part of it. But again we've go 6000 letters or something. I could look at the whole gene,

  • we've sequenced that, and again this is in homo sapiens, right here. So what we could

  • do is now we could line that up. So this is just like that telephone game. We could line

  • it up next to another organism and we could see how related we are. And so let's do, let's

  • see what would be a good one to do, let's do a platypus. So let's compare that same

  • gene in humans and in a platypus because we've sequenced the platypus genome as well. And

  • what you'll find is that I can look at similarities. And so this would be between homo sapien right

  • here, between us and a platypus we find that there are actually some similarities right

  • here. There're some similarities right here. So we actually share some of these genes with

  • the, portions of this gene with the platypus. But if I keep moving down and down and down

  • and down, we find that there's really not that much in common between me and a platypus.

  • But probably way more between me and a platypus, since it's a mammal, then me and for example

  • a tree. So let's compare something else. Let's find something that's a little closer to home.

  • Let's try a chimpanzee. And compare that gene in us and in a chimpanzee. So let's try that.

  • We're looking at blast data, so this is sequence genome. So now if we look at us and a chimpanzee,

  • you'll found, wow, there's an outstanding amount of overlap between us and them. All

  • the way down that gene there's a huge amount of overlap. And so we can compare that and

  • we can tell who's related to whom and we can also make these evolutionary relationships

  • a little bit more clear. Okay. And so when you hear a chimpanzee and I have 96% of the

  • same DNA, it's because of this. And humans are going to have, you know, 99.9999% of the

  • same DNA but some of that is going to make each of us a little bit different. The last

  • piece of evidence we have is, not so much evidence but it's a way to see how evolution

  • takes place. And that's using population simulation software. And so what we have here is a way

  • to simulate a population. Now remember, if we, let's run this for a second, so this is

  • a population the size of a 1000. We're just looking at one allele here, so we're looking

  • at one gene and its two varieties of the gene. And so if we look at this, this value

  • up here would be my p value, this right here, let me change it to a different color. This

  • would be my q value. And then here are going to be my different genotypes. And so if this

  • is, let's say this is big H and his is little h and maybe we're looking at Huntington's.

  • Then this would be homozygous dominant, this would be heterozygous and this is homozygous

  • recessive. And so we could simulate it again, so let me do that for a second. Let's go back

  • and simulate that again, and so chance is going to take over. So we could get a little

  • bit of genetic drift this time, but the nice thing about population simulation software

  • is it allows us to play around with those 5 different things, those 5 things that are

  • required to maintain this equilibrium. So for example we could play with a bottleneck.

  • So maybe we would want to make a bottleneck here from generation 100 to 120, where the

  • population goes from a 1000 down to 10. Let's try to simulate that and see what happens.

  • So now we've got 1000 in our population but now it's going to change, we're going to have

  • a bottleneck effect right there and so we could study how a bottleneck is going to effect

  • a population over time. Or we could look at mutation or migration or let's try fitness.

  • So let's say if you're homozygous recessive, let's say you have a 50% chance of survival.

  • So we could do a little bit of selection here and we could run it again. Let's try that

  • again, And now we have a p value that's going way up and a q value that's going down. And

  • we have almost the elimination of that homozygous recessive down here. So again, the evidence

  • that Darwin had for natural selection was a ton. The one thing he was missing though

  • was what we now have a really good understanding of now. So that's DNA and it's how DNA is

  • passed from generation to generation. And as it does that it leaves these wonderful

  • footprints that we can track evolution in. And so I hope that's helpful.

Hi. It's Mr. Andersen and welcome to Biology Essentials video number 4. This

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B1 darwin dna evolution gene evidence mutation

Evidence for Evolution

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    Morris Du posted on 2015/10/22
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