Bozeman science: evidence for evolution

hi it's mr. Andersen and welcome to biology essentials video number for this is on scientific evidence for evolution here's a picture of Charles Darwin much later in life Charles Darwin was very meticulous scientists who gathered copious amounts of data and to show that evolution was true and that his mechanism of natural selection was right unfortunately he didn't have a really 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 where fossil record 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 and the the whale have a common ancestor that had bone structure similar to like that or you could look at the rear legs why would a whale have rear legs and less at one point it actually walked on land and evolved from something like that and so today what I'm going to talk about is evidence for evident 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 macro evolution 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 we're living things are found I'll talk specifically about the galapagos tortoises next he talked about fossils example give you as a horse evolution over time next homologies or those are characteristics that organisms have that show common ancestry I'll talk about both homologous structures and vestigial structures and then I'm going to talk on a few things that Darwin didn't have available to them namely molecular evidence DNA is the trump card when it comes to evidence as far as evolution goes and finally I'm going to show you how we can use mathematical models to support our models for how evolution actually takes place so we got a lot to do so I better get started let's start with where Darwin started on on the Galapagos formulating his ideas and I've 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 some way from the mainland to the to the Galapagos and when you looked at the tortoise on Ecuador looks very similar there's no predators and so they were able to get very very big you can see there's 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 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 they're 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 you therrien's 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'd 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 forces have gotten larger and larger and larger as their environment has changed and they move from a more of a browsing to more of a grazing kind of an animal but we can see that growth reflected in the change in the fossil record in other words the teeth become flatter they moved have to grow have to run faster when they're out on the plains and so they move from many digits to just 11 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 newest thread all the way from those four first horses to the horses that we have today so horse of it our fossil evidence is really good there's some prizing a surprising amount of data on whale and whale evolution if you're interested in that you could take a look Nexus 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 the Darwin's tubercle which is like a little I don't 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 dogleg this would be a pigeon wing and this would be a thin of a whale and if you look at it you could definitely if you're an engineer design a wing more efficiently than 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 them 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 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 the primitive tail all those things are vestigial structures and 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 will call this person yellow makes a mistake instead of saying the fat cat ate the rat said the fat car ate the rat now that's the 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 Hoover here to pink pink does a nice job passing it on but then eventually we get another mutation here so we get a red mutation and now it's the fat cat ate the bat and now the fat cake car I hate the bat and finally the farc r8 the bath so when you get to the end the DNA is very similar but has 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 in that so they tell us a lot about who's related to whom in other words if you 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 would have been a lot he would have had a better that an easier job convincing other people that he's right so let's talk about some specific DNA evidence an example i'm going to give you here is the human fgf2 gene over the last 10 years we've started sequencing huge genomes in a genome remember is the sequence of all the DNA inside that one living organism the one I'm going to look at is one that it makes fibroblast wit so it's help helpful in healing of wounds and so we're going to go to this website 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 on fgf2 it's found on chromosome 4 and you could tell like how many base pairs six thousand letters long 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 exon so not really part of it but again we've got six thousand letters or something I could look at the whole gene we've sequenced that and again this is in Homo Sapien right here so what we could do is now we can line that up so this is just like that telephone game we line it up next to another organism and can 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 platypus we find that there are actually some similarities right here there's 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 than 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 sequenced genome so now if we look at us in the chimpanzee you'll find wow there's an astounding 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 ninety six percent of the same DNA it's it's because of this and humans are going to have you know 99.999% of the same DNA but some of that's going to make each of us a little bit different the last piece of evidence we have is 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 at the size of a thousand we're just looking at one allele here so we're looking at 11 gene and it's two varieties of the 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 the big P is Big H this is little H 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 five different things those five things that are required to maintain this equilibrium so for example we could play with a bottleneck so maybe we want to make a bottleneck here from generation 100 120 where the population goes from a thousand down to ten and let's try to simulate that and see what happens so now we've got a thousand 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 affect the 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 fifty percent chance of survival so we could do either so 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 a Q value that's going down and we have you know 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