Our last notes, chapter 19, the evolution of populations. Um, I just love this unit and all the topics. So, again, I'll try to keep it down, but it's hard. This one is only 30 slides, so I'm hoping I can keep it under an hour and 20. I will say I have mixed up some of the stuff in the chapter. So both chapter 18 and 19 there are things I took out of both completely like I'm not covering certain parts that are in the book. Also some stuff in chapter 18 I moved to 19. Uh I don't think I moved anything from 19 to 18 but there was the speciation stuff that was covered in 18. I moved to the end of this. Um I wasn't crazy about the way the book presented it or kind of the order of how they did it. And it's always interesting because different books focus on different things. So I sort of had to pick and choose what I could cover in our given time. So one I am trying to make it what should be covered in our course learning objectives. Um but and I'm taking out what I don't need to but I'm also trying to rework it where it'll fit in. So anyway, some stuff that was in 18 is at the end of this and and there is some things I've added to both because I felt there was more emphasis and they didn't um cover stuff that should be covered in our course learning objectives. There was some things in chapter. So know that you are tested over what is in the notes. So this lecture is going to be about the five mechanisms of evolution and then focusing on natural selection um and speciation. Uh so natural selection essentially can lead to speciation. Um remember well not remember but some things I even covered in that evidence for evolution that um modern research has verified a lot of what Darwin proposed. Um Darwin didn't get everything right and um there was a lot he didn't know because he inferred genes which I I'm still always just amazed about but didn't know about them because he was not aware of Mindle's work. But we do now and because of sequencing it has just changed our understanding um of evolution and medical treatment. I mean sequencing understanding the structure of DNA and DNA replication and transcription translation and being able to sequence the DNA and know the result of the gene or I should say the protein from a gene is has just changed everything. So um some things to remember as I go through here variation must exist in population. We know that that variation um genetic variation comes originally from mutations but will spread through a population and different individuals show uh different half differences within any given population. This variation must lead to these differences in lifetime reproductive success. So that's what we call fitness, right? How many essentially how many genes are they leaving as an individual? How much offspring um are they leaving? That could be done by different ways, right? It doesn't necessarily have to be a longer life. It could just be a way of reproducing more or it could be living longer to reproduce more. There's different ways you can increase fitness. Um and then of course variation among individuals must be heritable. That has to be passed on. All right. Back in the chapter 18 notes, I said that the simple definition of evolution is change in gene frequency over time. Really, that is like change. Oh, here I have it. Things change in alil frequency over time, right? If you have there are different alals for a given trait, essentially remember these different variations of a gene that causes differences among individuals. the ones with the alals that are more suited to the environment are more likely to pass them on. That's natural selection. But there are other things that can change the alil frequency, how much there is of a given alil in a population. And so I'm going to go over these leading up to natural se selection um after I go over the other four. So mutations uh lead to change in alo frequencies because now like when a mutation happens it could be a new alil that was never there from before. So it went from zero to now you know maybe 0.001. So frequencies are in decimals. So they're going to be between 0 and one. Zero being none at all. One being 100% of you know a population has that alo if that's the case. But remember mutation rates are generally low. So the other mechanisms of evolution tend to be more important um in changing al frequency but mutation is very important for natural selection and evolution because that is where the variation comes from right it's our ultimate source of genetic variation which makes evolution possible. Um and there is there's a a well-known population geneticist around today that is arguing that mutation is really more important than natural selection. Um and he's more he's not just arguably more important than natural selection because obviously it is very important because it leads natural selection but more important in changing a frequency. Uh so you know we may adjust our take on this in time but um something to remember too right the likelihood of mutation is not affected by lateral selection. The environment what alles are being passed on doesn't make the mutation itself more or less likely. That is just the random events that are happening in DNA replication. Gene flow. Gene flow is the movement of alals from one population to another. So it's essentially you can think of it how genes um spread. It can help them spread. So homogenize and keep uh you know spreading the alil to other populations keeping them sort of genetically similar. If you have an isolated population where you'll have a little gene flow right if a population is isolated there's not a lot of genes leaving or coming into it. Um so it can become different if it'sated. So right this can change alo frequency. It can keep it constant. reducing gene flow could potentially um cause then alo frequency to change. It could though, right, a a beneficial al that seems to help them like right an enzyme that helps digest food a little bit better. They make a protein differently now that serves as an enzyme that's beneficial. So, it's going to be spread throughout different populations. Um, so gene flow can affect um the how common alals are. I really hope I linked to this video. Okay, I think I do. I might have it embedded. I don't know how you're going to watch with me on it, but uh if you click on it and then hit like the uh watch on YouTube, I love this video. So non-random mating changes dream frequencies. So if you think about it, random mating is any individual of a given species is randomly mating with any other individual of that species. I I hope me just saying that you understand how absurd that is. And this is for almost any given sexually reproducing species, right? If a flower that blooms in Oklahoma, that same species of flowers can be living in Canada, but it's probably not going to be reproducing with a flower in Canada. That is nonrandom mating. A flower that blooms early in the season, even if it's in Oklahoma, probably won't reproduce with the same flower, that species that blooms late in the season. Um, right, humans don't just go out randomly around the world and mate with any individual around the world. That is non-random mating. So if there is non if you're not just mating with any other individual that species that is non-random which can change alil frequencies cuz certain alals could be favored for various reasons. The alil of the individual who's living longer might might reproduce more or who has a coloration that makes it appeal to the other sex might mate more. um who is able to avoid predators again surviving might mate more one who can produce a female who produces more eggs might leave more offspring. So, um, any sort of non-random mating, this is not just sexual selection, which we'll talk about a little bit at the end, but kind of extreme non-random mating in a very, um, uh, extreme form of sexual selection. We see in a number of birds of paradise and also some fish, particularly tropical fish, where you have large sexual dimmorphism between male and female, the the sexes of a species. Um sometimes um one sex really prefers certain attributes of the other sex where they and we call that sexual selection where they have evolved traits that might even be detrimental to their long-term survival where they may not fly as well or stick out to predators but um it attracts mates and they might be able to reproduce more. So we see some of these extreme examples in areas where either there's lots of niches to fill. So they could either avoid predators or sometimes where there is low predation. So there's not while there might be predators, there's not uh strong predation where they really have to camouflage to miss. Because if you watch this video and some of these birds the how noticeable they are if you think of like a peacock right that sticks out a lot and can't get around too easily. Um so this video is really funny and it shows a bird that has a very elaborate this male bird has a very elaborate dance to court um a female potential mate and you can see the differences between the male and female clearly in the video. All right, our fourth mechanism of changing a population is genetic drift. Um, genetic drift are these chance events that affect alil populations. I mean, sorry, alle frequencies in a population. So, how common an alil is. Um, there's going to be two types of genetic drift. I'm going to talk about uh bottleneck effect and founder effect. But in general, genetic drift is much more strong. we see it make a really make a difference an evolutionary difference in small populations because these are due to chance events or catastrophes some things that happen. So if you have a really large like a huge population where um like maybe a species that has a large range and individuals are able to move around a lot and active at different times and are often mating with many other individuals of the species, it won't matter. But if you have this small isolated population and some catastrophic event comes through, you can easily take out a lot of um alals in that population and it it's not due to them being better fit to their environment. It's just who survived the storm or whatever it may be. Um, it can also cause a harmful uh an increase in harmful alals if those are the individuals who survived even though maybe they have some sort of genetic disorder that is not great for survival. Um, I will talk about the blue people of Kentucky in a minute in one of my in my sort of two specific types of genetic drifts we think about bottleneck and founder covered on the next couple slides or few slides. So I should say on the last slide I said um a catastrophe that is a type of genetic drift. Genetic drift is just a change in a little frequency due to chance alone whatever that chance may be. Bottleneck is when the population um is drastically a population is drastically reduced because of something that happened. could be a catastrophe, could be a natural disaster, um could some random chance event that wipes out a number of individuals. So that's shown here, your individuals, many individuals get wiped out for whatever reason. And so those that make it through, those surviving, the few the individuals who survive this event are the ones that are passing on their alo. So you might not have as much variation after some sort of event like this. I have an example on the next slide. So northern elephant seal um is a bottleneck case study where they were hunted to almost near extinction in um the 1800s. only around 20 individuals uh in a small population survived and they you know kind of protected and mated and have now grown to thousands and thousands but there's really not a lot of genetic variation like they're they're genetically fairly similar. This is very risky. We don't like this happening particularly with um some of the larger vertebrates that have long reproductive times because when you get um a population that is too genetically similar, there's not as many differences and they can't handle certain changing of environments changed rapidly. It's hard for them to adapt to that because there's not a lot of genetic variation and there's not a lot of variation in offspring and they take a long these generation times matter how fast you can reproduce, right? Because if you're reproducing, if you're having lots of offspring in very short reproduction times, those mutations can arise pretty quickly. But with large, particularly large mammals, they don't have a whole lot of offspring and they don't have long generations time. So there's not as much gener variation. It takes longer for variation to accumulate. So if there's a changing environment, they can die out really quickly. They can also become inbred very quickly. 20. It's really hard to bring back a population from 20 individuals. Um but they did. But there's not a whole lot of genetic variation. That's because they all that are around descend from the same 20 individuals that survived hunting. um in time genetic variation will increase if they don't get wiped out. Uh and if they they hopefully have enough stable environment they can survive in as well but you would in time variation should increase. Another type of genetic drift due to chance is what we call the founder effect. essentially the individuals who um migrate and start a population, they're the alals that are passing it on. It's not that their alals are necessarily better fit to this new environment they've came into. It's just that they were the ones who got blown off course or migrated over to a new place. And so they have this bounder effect. So we see this like with island populations where individuals who make it to the island, right? That's what gets passed on. So with Darwin's finches, we we see this in them as well, right? They all descended from the ancestral species of finch from mainland South America that made it to the islands and they have adapted and became these different species over time. But there is are certain traits that are not necessarily makes them any better fit for the environment. They all have just because the those first few finches that came over had that that was in the population, right? Um so we see a number of founder effects. On the bottom right I have some of like human traits that are from founder effects. Blood type has to do with those individuals who migrated to some area and had that blood type. And so descendants, if you're from that area, you have that blood type. Certain rare blood types are like that. PTC tasters, lactose tolerance, right? Most lactose tolerance um certain European um certain African kind of like Western European and Western African, those were areas where lactose tolerance evolved if I remember right independently in both. I think there's some Middle Eastern populations. And so if you're descended from those populations where it evolved, you have lactose tolerance. The ancestral form is lactose intolerance. Most of the world was it like still is was um and still is lactose intolerant at as as adulthood. We call it lactase persistence. The lactase enzyme stays active. But a number of populations it evolved a mutation and spread. And so descendants of those populations have it. Um the blue people of Kentucky, I said I would talk about them. Uh there's um remote area in Appalachian Kentucky where a guy from a French I think he Yeah. Frenchman who came there, found it there um had this rare disorder that causes essentially a bluish tit to the skin. Um somebody else I think he had a relative who came too who had it. um it's not a wasn't a large area, fairly isolated area um not a number of people to breed with. So this alil became common. And so when you look at how common this alil is in this town or this area compared to most other geographic areas around the world, it was way more common there than in almost anywhere else because the founders, two founders had it and it spread within that town. So you have founder effects usually small where you have alo frequencies that change um due to usually they're due to chance events and typically are exacerbated in small populations. Okay. So now let's get to the heart. Right? The main mechanism of evolution is natural selection. Um we focus on mutation because that's where the variation comes from and then it being passed on. Those others do affect aloof frequency but the major one across the globe is natural selection. We have phenotypes that vary. Some individual leave behind more progyny that's just offspring than others. Um, and the phenotypes that are better adapted to the environment are favored, meaning those are more likely, the individuals with that are more likely to survive and reproduce overall at greater numbers, right? It might not happen in every generation, but over time. So, um, I'm going to list another direct I've told you we had a lot of direct evidence of evolution particularly of natural selection because we've been studying many species um, some of them for decades over time now. And one of the first classic examples of natural selection was um a guy would go out in England and essentially go out in the forest and take um counts of different species and the variation of them. And so he would looked at these peppered moss which had a light form and a dark form and he found the trees um were lighter at the time. They would have uh look there's a light one right there. lighter at the time, some dark coloration, and he found that there was a lot more of the lighter colored moths than the dark moths. Well, he kept records um and they he covered them, he covered kept counting them for decades and decades. And he actually passed on as data as well. And as the industrial revolution occurred and a lot of pollution was put out and covered the trees in soot, a lot of the trees had this dark covering in rocks. This is probably a rock here um in the forest and areas where they looked a lot darker. And so what he noticed was that the dark moths became more common. So right this is a change in alil frequency that there's alals that code right the I don't know which one's dominant dark or light. Let's say the light is dominant and the dark is recessive. The recessive alil increased as there was dark coloration and the light al decreased. That's evolution. there was a change in gene frequency. Well, people continue to follow this and as um there became more regulation and better um technological advances, less soot was put into the air, some of it was cleaned up, some of the forest recovered. Um and you had some areas where you got with new growth had lighter colored trees and guess what happened? The lighter colored moss increased in numbers. So right, this is natural selection. The environmental condition are determining which individuals have the highest fitness and the offspring are pretty much adapted to their parents environment. So if it's changing rapidly, it's hard to keep up because you might not have that you're not going to have necessarily that much mutation in a given year or even enough variation. But um if you have some variation and enough individuals with these different variants, the population can sustain itself even with changes. But how fast changes happen can make a difference as well and the reproduction time. Insects tend to reproduce pretty fast. So you can see rapid evolution in them compared to like a mammal. So evolution is the change in alo frequency over time. So it's something that changes the outcome over some time period. Natural selection is the driving force, the driving process that leads to evolution. Exactly over time. Evolution driven by natural selection essentially makes us assume that populations will become better adapted to their environment over time. couple of the examples of natural selection that humans have caused because we've changed the environment that um have are causing lots of problems for us today, especially the one on the next slide is um pesticide and antibiotic resistance. I'm going to talk about pesticide on this slide and antibiotic resistance on the next slide. Um so pesticides are usually some sort of chemical that kills what we see as a pest that we don't want. Typically, this is with crops where we don't want them eating our crop. Um, and so we spray it with something. Um, there are often chemicals that essentially the species can't detoxify or metabolize and so it kills many of them. But some of them, right, there's variation in a species. Some of them might have some resistance where unless if they're getting completely doused it, they can survive the amount. And then some individuals without that variation are still going to survive because they don't get sprayed directly. They're not they're underneath some. So like the white here is showing not resistant. They're susceptible to the pesticide. And the red is resistant. Um right pesticides not going to kill every pest of that species. It's just killing their crops, but there are other ones who live nearby who can come in. So it takes a while. might take some decades, but over decades of use, um, many insects have become resistant to pesticides because those that had the variation that could metabolize the chemical in some way or break it down um, survived better and had more offspring and so they became more prevalent. And now we have a number of insects resistant to a variety of pesticides. Um, there's different ways of dealing with this. are some ways of targeting pests that don't use pesticides. So like bed bugs don't give disease, but they are a nuisance in your house. Um, and will bite you up. My graduate work was on a relative of the human bed bug. It's a bed bug for birds and they are actually detrimental to the bird's survival. They're not as much detrimental to human survival, but they are not pleasant. um today, while they still might use pesticides, um a treatment for that is to heat it up. Essentially, seal off your house or apartment or hotel room or wherever it might be and heat it up really hot because the heat is uh it's less likely that the insect is going to evolve resistant to this heat because it gets really hot and they also don't do well in very dry environments. they do like some humidity so that kills them off and then sometimes they will put in a residual pesticide pesticide after treatment to try to keep anything that might have crawled in between rooms. Sometimes they get in the wall and can kind of get away from that heat. Um, and what we've gone to using is more of a cocktail like essentially using multiple types of pesticides because it's very hard to evolve a resistance, right? Right? If you're using m like three different types of pesticides that work in three different ways. Even if they did evolve a resistance to one, there's two other ones that are going to kill them. So that bug is still going to be killed and not pass on its resistance. We've done this because we saw this successful with HIV treatment. When we first got HIV treatments, we would give an antiviral drug, but then the people that were taking it, the virus inside them would essentially become resistant to that drug. So it would do good. it would be helpful for a while but then it would become resistant and the HIV was a problem. So what we found was giving a cocktail like three antivirals that work in different way the virus couldn't evolve resistance to it when it was trying to replicate. If it revolved resistance to one it's still dying so it's not passing on that resistance and it it didn't evolve resistance to all three in one or few generations. And so that became a very successful treatment in treating HIV. Um and so now we've kind of started using it in pesticide resistance. Let me talk about antibiotics resistance on the next slide. Antibiotic resistance is very similar to pesticide resistance where um you give an antibiotic. This has came from overusing them both um in agriculture and in people. So like in a person you're prescribed an antibiotic. What happens is you're killing off the bacteria when you take it, but you start feeling better before you finish your prescription typically because the bacteria is reduced to down to where it's not causing symptoms and people would often stop taking when they feel better. We also had an issue of prescribing antibiotics when there were viral infections. Um, and antibiotics don't work on viruses, so they were really unnecessary. And so what this meant was that a number of bacteria that if there was variation and they could metabolize or break down this antibiotic, those are the ones surviving and growing back in people and animals and around in the environment. And so now we have today we have a number of bacteria that are resistant to um antibiotics. And and part of a big problem is that we have very limited antibiotics. There really only two large classes of antibiotics. we have different types we use from them that are slightly different but they all kind of come back from the same similar class so they work in a similar way. So, we really need more types of antibiotics. And if we could use, right, if we have more types, we could do these cocktail treatments and they could be successful where the bacteria is less likely to evolve resistance to um the cocktails because even if it had a resistance to one, as long as it worked in a different way, it wouldn't evolve resistance to on the others. But, uh part of our problem is we don't have a lot of variety in our antibiotics. And today we are um really scrambling to find some. We really need some good methods. This is I'm very optimistic about science, but this is one of the areas particularly medicine that really scares me because um antibiotic resistance is a huge problem. And while I do think we're going to find some methods that will work better, hopefully various other types of antibiotics, we don't have them yet that are successful enough. So hopefully we will find something to help us. So natural selection, major driving force behind evolution. I'm going to talk about some things with natural selection. Some of this was covered in your chapter 18 book. I'm covering in these notes. Um and how this leads to speciation. I'll say some stuff about speciation towards the end too, which I think that might have also been covered in 18. Um so Darwin thought evolution occurred very slowly and it can but um we and really until mid 1900s a lot of biologists were really looking at things that have happened in the past but since about the mid 1900s we've had scientists who have studied um species long term and made lots of observations around the world and we've been able to document like those ones I talked about different cases of natural selection and we've seen different types. We realize that like the way it's happening different ways. So we have three really broad types of natural selection. I'm going to talk about disruptive which your book uh your book uses a different term. It's on the next slide. Can't think of what it's called. Um directional and stabilizing selection. Um something else I kind of noted this but I want to say specifically as we go forward too. Sometimes you'll hear the term um natural selection as survival of the fittest. Darwin did not say this. Somebody later coined this term and it's often misunderstood. Right? In biology, fitness refers to the number of offspring you're having. So, we're not saying necessarily the biggest and the strongest. It's just who has a better chance of surviving in their environment to pass on their genes. Um, so really it's the increased fitness that is what natural selection is. So we have these three types of ways populations can essentially diverge. There are others but these are the three common ones we see. Diversifying that was the word I was looking for. So disruptive or what your book calls divers diversifying. I've almost always heard it as disruptive. I was a little surprised by them using that term but maybe that's a new way it's going. Replacing disruptive selection. This is where so in a population I'm going to draw a little curve right in a given population a phenotype how many individuals have a certain phenotype there's some variation there right most individuals the majority of individuals kind of have this of the phenotype and a small percent of individuals has the very extreme end and a small percent of individuals have the other this is like number phenotype are on the other end and most there that's how we kind of think of as a population in this normal sort of curve bell curve. These three types of selections show how it kind of changes based on the environment. So with the disruptive selection the extremes are favored. Essentially those who have those extreme phenotypes are what is being favored. um hypothetical described here in from your book. I'm going to use a real world example. African backbellied seedcracker finches. We love our finches. Birds and fish are used as a lot of examples because they've been highly studied. So that's why they come from there. Other animals evolve too. It's just there's so many and they're really easy to study. So they're like a lot of examples come from them. So, um, seeds, these are guys that get seeds. And the seeds tend that they eat tend to be large or smaller. And so, what happens is that because birds with the intermediate kind of middlesized beaks have trouble getting at both the small and large seeds, they don't do as well. They don't really get as much food and don't pass on as many genes, essentially as many offspring. While the birds with the very big beaks, let me use a different color here. Very big beaks can eat those big seeds, they do well. And then the birds with those little beaks get the little seeds and get a lot of food and they do well. You get a disruptive selection where these guys do well and the guys isn't just plural. Those big beak birds and small beak birds and intermediates don't. So in time the population moves to being more of this curve which shown in red because um you have a high number of small beak birds low number of intermediate and a high number of big beaks. They're showing a different example here. You could read about disruptive selection. Directional selection is kind of the classic example that I think we think about. So it's going more one way towards one extreme. So this eliminates one extreme and the population as a whole moves towards the other extreme. Um that was like the moss went from light to dark. When they went from light to dark that was directional. Antibiotic and pesticide resistance is directional. They're going towards that resistance. Another example of direct evidence which I like. This was earlier in the year. you could have had an opportunity to go see Dr. Charles Brown, one of my graduate adviserss from TU, speak um about some of his work, this book he's writing. He has studied cliff swallows in Nebraska for um over 40 years now. And close swallows live in these mud nests on bridges uh and coverts so around trains, but they're really common on bridges. You see them around here. They build mud nest that looks like a gorge shape when they finish it. Um they're often flying around roads because their nests are by there and so sometimes they get hit by cars. Well, he studied them in Nebraska and he studies them living. He nets them, puts a band on them, tracks them, sexes them, measures wingspan, measures weight. Um but whenever he encounters a dead bird, like there's a dead bird on the side of the road, he would pick it up and note how it died. If a bird died in a net, he's very good about that. But occasionally one would die in a net, he would save it and note that. If he saw it dead, if it's dead in the nest, he would note dead bird in the nest and collect it. Well, so he's been measuring, he's been studying these birds, the living ones, and noting their wingspan and collecting dead birds and measuring and taking notes about he would know what type of sex it was, when it died, where it died, how it died if he knew it, and its wingspan and its overall body size. if he could do that like if it wasn't too he didn't usually take weight because that can change pretty drastically after death. Um but what he noticed in this 40 years was that essentially the bird's wingspan on either side became shorter like so it was as an average the population got a shorter wingspan not as long from tip from one tip of wing to the other tip of wing and more symmetrical. So, I'm not very symmetrical here. They're not perfectly symmetrical. None of us are. We're like, we have bilateral symmetry and we're somewhat symmetrical, but not perfect, right? And they weren't either. But, but he noticed as their wingspan got shorter and more symmetrical. And what he noticed was that the birds that got hit by the cars and died by the car had longer wingspans, further, like further from wing tip to wing tip, and were less symmetrical. Um, and the population as a whole over this time moved to more symmetrical and smaller wingspan. And what he realized was is being smaller and more symmetrical allows birds to be more maneuverable. Essentially, they can turn faster. They can be quicker. It's not great for long-term flight. Having that short wingspan, and they do fly really far, but not necessarily at one day at a time. They just they they go to South America. They overwinter in South America and then breed here but in little spurts. So they kind of have these competing things of getting shorter wingspan but they still need to do long flights. So it's probably not going to get super short. But having the shorter wingspan has a allowed them to now essentially avoid cars. So what was happening is the ones that were getting hit by cars had longer and more asymmetric wingspan. And so they're not passing on their alil and the ones that are surviving have a shorter more asymmetric or more symmetric wings span and allows them to be more maneuverable to avoid cars. And so they this is this is interesting because this is one of the few studies that have really shown animals evolving to humans, right? because of our cars they have d evolved their anatomy has evolved in direct response to us. Stabilizing selection is when you go from that you know average span where those ones in the middle are favored. So you lose your extremes and the population moves in and so then a lot more you have less extreme vast majority of individuals have the same type of phenotype and you have little variation above or below that um and it's only a little bit above or below. We see this in um birth weight of humans clutch size of many birds. So this is example here they use robins as example but there are many actually bird species this is a classic example for most bird species um how many eggs they lay is pretty close like like some birds might lay three eggs some birds might lay five eggs and most birds in that species lay about the same number of eggs you do have some individuals who might lay one or two more right so if it's five eggs the vast majority of that species is going lay five eggs. Some individuals might lay six, a very few might lay seven, and maybe like none lay eight. And then you have very few who lay four and even fewer who lay three eggs. Um, and so with this, it's kind of similar to the human thing I'll talk about in a minute, is that they find like too many um too many eggs, they tend to get malnourished because they can't feed them all and so they die off. and then too few eggs, you're really not producing enough that survive because I think I've said this before, but if I didn't, a species always produces more offspring than can survive. Some individuals going to die. And in nature, in humans, we don't think about that as much. It is true, but in nature, it's very much very true. It's a lot of varies there, but a lot of individuals are not going to survive. Like, right, a lot of eggs aren't even going to hatch. Some may just have something where it doesn't hatch. Some a predator is going to come and eat the egg. Some of those that do hatch are not going to survive. So if you're only laying three eggs, one maybe gets eaten by the snake that comes through. So now you're down to two eggs. The two hatch, one of them dies before it even fledges. Now you're just down to one chick and maybe it maybe it fledges, but then it doesn't make it act the next year. It dies on migration. Now you have no offspring who's making it back to reproduce. So um it kind of depends on the life history of the animal. But birds tend to have certain clutch size and some of the bigger birds have smaller like you know three maybe eggs. Some other birds might lay like five or six. Um with humans we see this in our birth weight. um most babies kind of fall at least naturally into kind of like a 5 and a half to eight and a half pound birth weight range. And we find that like below that survival was low uh in the offspring and above that this was kind of before C-section um often the mother didn't survive and you know historically speaking if the mother doesn't survive a lot of times the offspring wouldn't survive. There obviously are many cases where they have been taken on but they have to be nursed when they're young. So you have to have somebody to be able to nurse them. So uh once we had cultures and communities there's a way to help that but not everybody made it. It also sometimes because if the mother died in child birth the baby could potentially die too may not be able to be fully born and and died during it as well. So um kind of when she that's was more like over nine pounds. So most babies really fall into 5 to nine and the majority of those are kind of in the six to eight. Although um because of C-sections we have definitely increased survival on the higher end and because of NICU we have increased the survival on the lower like low birthw weightight babies. So we are essentially could be changing survival of these different birth weights. So we might see more variation you know over the next thousandome years. It would take a while, but we'll see as we have more interventions if that affects um birthw weightight of offspring. Okay, population genetics. Your book kind of focuses on this. Uh I do love population genetics. It's a looking at these alil frequencies, the gene pool, founder effect, genetic drift, how alals spread, and the change in alle frequency in populations. So if we can document a change we can say then okay this alil is increasing the dominant al's increasing the recessive al is decreasing what is causing that why is this increasing and why is it decreasing um and so we look at that and we use this formula and this principle called the Hardy Weinberg principle and Hardy Weinberg equilibrium to kind of determine if a given trait or alil is under a selection pressure. So these are these mathematicians applying their concept to biology where it's looking at alic frequency. If hard if a population is in Hardy Weineberg equilibrium then that means the alals are saying at the same frequency. Right? If one alil the dominant alil makes up 40% and the recessive al makes up 60% because right together they would have to add up to 100 and it stays that way over time then we would say like that alil isn't under a selective pressure. Um, on the other hand, if it changes, if it's dominant is 60% and recessive is 40%, and then you go back some years later and it's reversed, dominant is now 40% and recessive is 60%. Now, why did that dominant go up? Why are they not surviving as well? Or what is it about the recessive alil that makes it better adapted to the environment? Um so they made a mathematical model to look at this where they have p + q = 1 where p is the um frequency of the dominant alil. I should have it atalicized this and q is the frequency of the recessive alil. So like big a little a and together those would if that's we're assuming just two alals of course that's not always the case but in this case those would have to add up to one or 100 because frequencies fall between zero none at all and one being 100%. So they those are the only two alals they would have to add up to 100. Um I'm going to have a short separate slideshow to show how to do the math models. Um so there is another this can be reformed because you can't go into a population and see P and Q like right if you see recessive individuals you know that they are this but that doesn't tell you the frequency of little A because all the dominant individuals could be big A big A or big A little A. So you don't know the frequency of either one big A little A by looking at them. So they reworked the equation where it's p^2 + 2 pq + q ^2 and this tells you the phenotypic frequency equals 1. So this is q ^2 is the frequency of individuals who are little a little a or recessive. This is the frequency of individuals who are hetererozygous and this is the frequency of individuals who are homozygous recessive. So if you know if you go into a population and you see that recessive individuals in this population of 100 if 20 are recessive then you know that 2 is your two is your Q ^2 then you can take the square root of Q ^2 to get Q. So now you have Q and then once you have a number for Q you could solve for P. So, um, I won't have you do math on the test, but I do expect you to understand what P and Q equals. And, well, I probably won't. I could potentially ask a question about P^2, what P^2 and 2 PQ and Q ^2 mean. Um, so if you want to check out that, you can, but you can get by with uh for the final with what is covered right here. So just a little bit on sexual selection. Um sexual selection is based on mate choice where um one sex essentially has some sort of evaluation of the other sex and mates with them based on certain characteristics. How well they dance like in that video. How big or colorful their feathers are, how big they are, how small they are, how fast, uh different things. Um, in most cases we tend to see that females are more selective than males. Um, and in these cases, not always, in these cases, females tend to put in more parental investment. We do see it switched uh where we see where males put in more parental investment than females. In those cases, males tend to be choosier and tend to select something in the female. Sometimes it's size, looking for a bigger female that might provide more eggs or something. So, um it [Music] is variable. We tend to have more examples. Like I said, the fish, these birds of paradise, um are are the examples we've seen. So, those are often the ones we use. And those are where the males are very colorful and the m females aren't necessarily as colorful or large display or whatever it may be because they're the ones picking So dorphism mean d meaning two and morph morphology is where you have physical characteristics between the sexes right um birds shown here that's a p hn that's a peacock right that's a bit that's different spiders a lot of spiders you'll see right weaving those webs they're large the females are way larger than the males um oh they got some other birds here always birds right but I should had some I wish we had some more fish I need to add fish in the slideshow. But um these where you see pretty extreme sexual dimmorphism is usually because some sort of sexual selection is occurring like there's some choice or or something happening there that uh causes that. It could be in survival too like um like with mosquitoes only the female bites you. Males don't bite. And if if you ever see you can look it up. They're very tiny. But male mosquitoes have these big feathery antennas. Um it helps them essentially detect get to the female to to mate. But um where you have ex very extreme sexual selection, you often get these extreme sexual dimmorphism where you could see uh a major difference between the sexes. Not all like in the clols I used earlier, there's not a lot of dorphism. It's actually very hard looking physically to tell a difference between male and females. They're very similar. Okay, the last 10 slides, I think most of these came from or some things I've added to um chapter 18 where they talked about speciation and origin of species. I took a lot of it out because um they go into some stuff which is very interesting and good if if um the historically this class was bio for majors and we went into evolution a little more but with it being cell molec we kind of um keep it simplified so I took a number out I'm trying to keep it to just what you need to know. So I've talked about a biological species concept was in inter in a brebreed produce viable fertile offspring meaning the offspring can reproduce themselves. We get hybrids that's a cross between two species and we'll kind of talk about that because a species is actually really hard to define. We have other definitions of species because the biological species concept doesn't account for things as well. um and sometimes these hybrids. Um and so we do have other definitions we won't get into, but there are other ways to define a species. And a gene pool, this collection of all the variants of genes in a species. So speciation is when you have a divergence of one species into two or more like the finches before, right? Evolved into multiple species. Now, that doesn't happen all at once, but you can have multiple populations of one species become isolated and be diverging into multiple species. Typically, we kind of think of one to two, but it can happen more than that at once. Um so we'll be doing clatograms in lab but you have these common ancestors that these nodes represents a divergence where they had some common ancestor that diverg into two different species and then there's a line of species right that led this typically you know led to these two but there could be many that have led to that right so this is like um the uh what do you call Oh, a clatogram or fogyny here of elephants. So, this takes time. Speciation takes time. It does not happen overnight. And one like we look back in a clatogram and say, "Okay, these two species diverge." But that divergence, there still could be overlap where individuals are mating with each other. It doesn't just happen instantly overnight. So, um, there are different things that kind of happen along the way that will in time lead to two separate species. So, I talked about the finches before. I've actually said essentially what this is without giving you the term. Maybe I gave it the term. I don't think I did, but adaptive radiation is when you have usually it's rapid evolution, although this can not always happen so rapidly. um of one species into many different species. Islands are a great example. So island the honey creepers of Hawaii. You're going to see this in the lab you're going to do this week. Um ancestral species that evolved into multiple different species um usually based on kind of what they're eating, right? Their beak is their bill and beak thickness and shape very indicative of what they're eating. Same thing we saw with the finches. Some ancestral finch species got blown or you know a group got blown off course or flew over to the Galapagos. They were the founder and then they rapidly evolved. There was all these different niches they could fill. Essentially their role in the environment what they can um there's not a lot of competition. So if they get there and you know they eat insects and seeds, um some are probably going to start eating more insects, not a lot of competition. Well, others are going to eat a lot of seeds, not a lot of competition. And so then the ones eating seeds, their bills, the mutations that make them more suited to eat the seeds, their beaks are going to change a little bit. And the one who's eating insects are going to change a little bit. And in, you know, in time with other differences accumulating, they become different species. Again, not overnight. happens over time. We saw this with mammals. So, um, mammals have a common ancestor that goes back to the time of the dinosaur. There were mammals around at the dinosaur, not many, but they were had evolved to be warm-blooded, which was beneficial, and have hair or fur, and they could nurse their young. That's what makes them mammals, as I talked about last time. So when the there weren't many, but when that mass extinction of the dinosaurs happened, now there's a lot of available niches. There's not as much competition. All those these dinosaurs are dying out and now you have resources. So those few mammals survived because they were warm-blooded and had hair and fur and could essentially were able to survive that changing climate that happened. And now there's these open niches or niches, either one, they could fill. Um, and they rapidly diversified into lots of different forms. There's a little video, actually there's a long video. I'm going to suggest watching a small section of it. It's like 6 minutes at a portion of it um at the end and and it kind of you you kind of see very briefly goes into how that happens. Okay. So for speciation to occur, you have to have essentially some sort of rep reproductive isolation. There's going to be ways where they're not mating with each other. Individuals of a species are not going to be mating with each other. So you're not getting that gene flow. And we have two broad categories. We say preygotic isolation or postsygotic. Essentially before you make the zygote. So again, this is going to be specific for um sexually reproducing species. or after you make the zygote the offspring doesn't survive. So I'm going to talk I have a few slides on the prezygotic meth mechanism so I'm not going to talk those. I don't think I have any separate slides on the postsygotic so I'll talk about them. Oh there is one at the end about postzygotic but there's hybrid viability. So an embryo is produced but cannot survive development um or hybrid inviability. So two twos what are now different species right they came from the same common ancestor they were maybe different populations diverging but occasionally would mate at some point they will evolve differences where maybe they can still mechanically mate and make a zygote but then that doesn't develop right so now they've they've when these genes start getting turned on and off in one what is now one species, right? We think of it as what was a population, but now they're this is where it's hard to call species. Are they different enough to call species? They can reproduce, but the genes from one are trying to be turned on and off, and the genes from the other population/species are trying to be turned on and off. And as that cell is dividing, it can't do that. It can't control because certain genes have been triggered to be turned off in one and on in the other and they don't match up. So it stops being able to it stops developing and ends. Then you can have hybrid sterility and this is the mule example. Horse horses and donkeys, right? Those are domesticated. Um we we bred the ancestor for specific traits. They're obviously closely related because they can reproduce and make a mule, but the and the mule can grow and develop, but it is sterile. It can't have offspring for the most part. always some random exceptions, but I can't I'm going to talk about prezygotic on the next few slides. We have temporal isolation. That's essentially things happening at different times. Um I always like my flower example, right? If flowers are blooming early in the season, they're not reproducing with the same species of flower re um blooming late in the season. That's a temporal isolation. They're blooming at different times and so they're not sharing their genes. So in time, all those flowers blooming early in the season are going to be reproducing with each other. And if one of them has mutation that makes them like better adapted to maybe the cold weather because it's cooler and so they now that maybe they can survive as freeze better or something that would be beneficial and it gets passed on. While the ones um blooming late in the season, they ones that have a mutation for dealing with colder weather makes no difference because the weather's not cold. So it doesn't help them survive any. So like that doesn't get passed on. And so they'll start the the mutations and that variation that makes them better adapted for their time when they're blooming and who they're reproducing with as to what's going to be passed on and in time they can become different species. Habitat isolation when you um get things that are separated um you have um like mountain ranges, right? on mountain ranges they change the related to pangi and the last notes continents move um that can cause mountain ranges to form erosion can cause mountain ranges to get reduced down so where there's when a mountain range forms over time or continents separate right you were together as one species now you're an ocean apart you're going to diverge and become different species um and behavioral isolations the actions or how they act um can cause them to not be able to breed. And I'll talk about that on the slide that it's on. So, I used my flower example, but your book has uh an example for frogs. Um ran a genus of frogs where they're closely related. So, if you see the same genus name, you know they're closely related because that means they're in the same genus. So, they have a common ancestor, a recent common ancestor, and these two frogs breed um at different times of the year, right? Their common ancestor at one time, probably bred across, but then there's differences, and so one now breeds earlier than the other, and so they don't breed at the same time, and there's no gene flow between them. Well, I say none. There might be some overlap, but probably unlikely. Habitat isolation. We've seen this in um vertebrates and invertebrates. So here is a study in crickets that showed right same genus closely related species had a same common ancestor that was one species that has now diverged to two and a lot of that seems to be based on the environment they pick. One prefers more sandy and one um prefers more lomy soil. So they have different environments. Uh we've seen this in um lizards too and um other types of reptiles where preferring like they're closely related species found on the same island. So right they're in the same environment in some ways the same major environment. You think a similar habitat but when you think of that niche they fill it starts to become different. Some prefer the tree while some prefer the ground. So now some are more are spending more of their time getting their food and mating in the tree and some are mating down the ground and in time they differentiate into different species. So that's that's kind of filling that niche that specific role in their habitat that they're doing. They can be in the same place essentially but when there's differences within this small differences in the environment those can be exploited. So another prezygotic barrier is like gdic barrier. Um right postzygotic is they are able to produce the zygote but as species differentiate at some point usually there's going to be there will be prezygotic methanis the prezygotic can happen like the temporal right they they could still mate if they were potentially by each other but they're not because they're filling different niches or being in different parts like that habitat isolation and so in time as differences accumulate and some of those differences might be the ability to reproduce. So like these interesting are the shape of the male reproductive organs among damsel flies right and each wild I know and each of those are only um compatible with compatible if I can talk with the female of their species right they've diverged differently part of their divergence is their anatomy and their anatomical parts that is going to be specific with who they're mating with um fish, right? Most fish release sperm and egg into the water. So, they go to each other, they release their sperm and egg. When they're differentiating into a different species, right, there could be hybrids there. So, at some point, the sperm is going to be different enough or unable to fertilize that egg where it doesn't make the game. And this is due to accumulations of mutations, variations that um cause it to be different enough that it can't do that. So, I've said it before, speciation takes time. It takes um thousands and thousands of years. Typically, you're like hundreds of thousands of years before you actually get divergence to enough differences to two different species. And part of that is because of those pre and postsygotic mechanisms. And there tends to be hybrid zones because a species differentiate and you have these different populations that are accumulating these differences. Some individuals are still going to have some gene flow. Few individuals are occasionally mating with few individuals of another population. And so you're introducing those alals and going between populations. And so that hybrid is when two separate but closely related species continue to produce offspring. So it's where they still can produce offspring but they differentiate so much and it's so rare. We call them different species but they really can make a hybrid which and sometimes the hybrid um can survive. Sometimes hybrids are weaker and sometimes hybrids do well. So this is where we have reinforcement, fusion or stability. So this is where hybrids are less fit. So sometimes a hybrid is produced but it doesn't do as well as either of the species do individually. So the species continue to differentiate and go on to become different species. um fusion kind of the opposite is where the hybrids still do well. um the or the barriers weaken like they're not a they start separating and occasionally make hybrid and the hybrids maybe do okay but something maybe a mountain range was forming or maybe a river was forming water's coming through but then something happens that fills it in a landslide and now this river has filled in and now there's not difference and so there's easier gene flow and so they're mating again and making lots of hybrids and they become back to one species. See, this is where I it's this is why it's hard to say a species. Like, can you really say they're two different species if they're making this hybrid if they have the possibility of coming back to one? This is just maybe two very distinct populations. It's where it gets very tricky that were diverging and on their way to becoming different species, but then the barrier went away, so they came back as fusion. Here it says separate species, but like are they separate if they come back as one? That's hard to define. And then stability is where the species diverge and separate. And then occasionally hybrids are produced. And the hybrids um do fine, but it just they just keep going. Like it's not close enough that they diverge or separate. It's just usually this is like when hybrids are rare, but they survive. All right. And they just kind of go. the hybrid goes back into one of the populations and mates with like this population and so most those genes get there and then like maybe another hybrid's made another hundred years later and it goes back in there. Like sometimes a hybrid's made but it just gets back in and it just sort of stays that you have this hybrids that are occasionally made and usually just go back with one or the other. Okay, so that's speciation in the more the small scale when we're thinking about it. It's happening in the environment formed. A lot of times students lead to the questions, well, how about if we keep going back, right? You I keep saying we're all related. Where does that go back to? Well, there's more to it that that's really beyond the scope of this course. So, I'm going to gloss over a few things just so you have the information. And this is stuff that I could cover on the test, but I wouldn't ask much about it because um it's not really in depth in your book. But all living things have some relation, right? We all have DNA, RNA, the same base pairs for those. We have ribosomes. We have that universal code, right? The same code on cones codes for the same amino acid regardless what organism. A lot of us make, all of us make all some of the same proteins. The amino acid might be different for those proteins, but we all make the proteins for glycolysis and to produce our cell membranes because we all have cell membranes and then we have cytoplasm and do what you've learned about in this class are mostly universal processes. So where do we go back? Well, we can't of course know exactly how life on Earth started because we weren't there and we don't have a record and we can only go by what we know. We know that Earth was fairly inhospitable for about almost the first billion years. The atmosphere was quite different than what it was today. A lot of electrical storms, mostly water, volcanic activity. Um, not great conditions for life. But having water is very important and that electricity is also important and having the elements. There were elements present particularly a number of carbon both in the atmosphere and the water. carbon, nitrogen, oxygen, some phosphorus. A phosphorus is in that rock. So, as the volcanoes form, we got some phosphorus. Um, I feel like I'm missing something. I say hydrogen, it's there. Obviously, oxygen, hydrogen are in the water and in the atmosphere to some extent. So, we say we had this more primordial soup. We had the elements in inorganic molecules. There wasn't much organic, although there would be some methane. Methane was common as through a geological process. So methane was present but the organic in the form that we need for our organic molecules was not present but the elements were there and so the right conditions could lead to the formation of organic molecules. Um, so some have thought and speculated that maybe the organic molecules came to Earth by meteorites. Something the the, you know, meteorites, asteroids, the Earth was being pelted with many of this in in our solar systems earlier years. There's a lot of material out in outer space that was more was actually coming to Earth hitting. So things could come in and those were rocks and it's potential there could be organic molecules on there. We can't rule it out, but we don't need it. It wasn't necessary because we have shown evidence that life on Earth could have evolved on Earth without getting organic material from outside of Earth. So this has been done replicated since and we have better evidence but I'm just going to summarize the early experiment in the 1950s back when good old Watson and Crick are figuring out the structure of DNA Miller um did a classic experiment like I said it's now been replicated and expanded on but it was the first one to show that you can essentially make amino acids from inorganic material. So they put the elements needed essentially for amino acids, simulated early earth conditions with the warm water, electrical currents, electricity, um had gases present and essentially were able to make amino acid. Right? Here's the gases present. um make amino acid amino acid like molecules organic molecules with carbon and hydrogen attached monomers that could be built to make polymers had them present. Once they are present they just they have to come together to make the parts of the cells. Now that takes another step but making them was an important part. So um this is a way that why you know a lot of biologists don't think it's likely that earth um the organic materials came from outside because they didn't have to. We have shown that they were able to be produced here. So um we don't have to think they had to or rely on that. So that would be how we find uh or had earth's early organic molecules. Um those would have had to form together to make you know the the materials that make living things. Genetic material evolved at some point from that. We are pretty good. This is as far as I know it's still considered the RNA world hypothesis but honestly it's on its way to becoming a theory because we find like every year I hear a new story about more evidence supporting this. So, um, there's a number of evidence supporting this at this point. I honestly don't know the most updated one cuz I haven't followed it very well the last couple years, but I do remember a pretty big news story though a couple years ago um, supporting this evidence. So, or more to support it, I should say. RNA world hypothesis states that RN R RNA was the original genetic material and that the earth's earliest living for organisms just used RNA and then later DNA essentially evolved from RNA. So RNA of course is uricil instead of thamine. RNA I keep saying remember how I kept saying it's the workhorse of the cell like DNA holds information but it doesn't actually do anything. That's because RNA was around did all this stuff. RNA can self-replicate, can have enzyatic activity, essentially work as an enzyme. That's what a ribosome does. Can be structural like a protein, a ribosome, um, and has various other functions. It does a lot in your cell. But the thing about RNA is it's not super stable. So it was around and probably used as the first genetic material. But at some point DNA evolved from RNA and that probably then served as the genetic code that could be passed on easier like passed on in a stable form. So a lot of you asked like why is there uricil instead of thymine or thymine instead of uricil? Thymine is more stable than uricil and DNA having thymine and being double stranded makes it more stable. So DNA will last a long like thousands of years longer than RNA. RNA actually degrades rather quickly. Like RNA with some heat exposed to certain elements, it can degrade within seconds. DNA can last like we've gotten tens of thousands of year old DNA from specimen. So DNA can last a lot longer than RNA. And so it most likely evolved as a more stable structure to pass on that material, genetic material, and hold that genome code. And I made it under an hour 20. Thank you for sticking with me for this lecture and any others you have listened to. You've been a joy to have in class. This last one links to a video like the whole video is great. It's an older one. Um David Atenboroough narrates it. We all love him. He does all those planet Earth and all those sort of naturalist videos. Um, this is an old one, Natural Selection. It's like a movie. It's very long. It's not very long, but it's um it's a movie, a documentary essentially kind of about evidence for evolution. It's from I guess I thought it was older than 2009. Um, but it's very well done and it's all still very applicable to today. But I like this little section. I show this in my in-person class and I have them answer some questions on it. I recommend just like click on the link and then going to this about this minute and watching these sixish minutes of or five and a half of um watch that and um I recommend it. It's just a good a good viewing that ties into lab nicely because it shows a clatogram and how species kind of evolved from other species and where life formed and how it took on its different things all summarized in five minutes. So, um I highly recommend it and wish you the best.