now the next slides we're going to be discussing are going to cover microevolution and i'll discuss later why this is pretty much all there is in evolution there really isn't anything beyond microevolution everything else beyond this is just us coming up with different words to try to like organize things better everything to do with evolution comes down to microevolution and there's gonna be five parts of it and these will be familiar because they'll be the opposites of what we've just talked about when we did hardy-weinberg equilibrium they will sometimes have different names though so make sure you're familiar with the terminology so for instance instead of saying small population size which is certainly something that can lead to evolution we call that genetic drift so the way genetic drift works is when you have a small population it is very very likely that you could lose alleles that you possess by chance so this is kind of showing this population that's very small that starts out with two different traits a red color and a blue color the dots you see refer to how many offspring each individual had so you can see based upon who's most successful at reproducing which with chance you're going to get where certain individuals might just end up dying just freakishly so to speak they might get a disease that leads to infertility or otherwise inability to find somebody i mean there's all kinds of stuff that could happen they're just not interested in reproduction to make it where they do not reproduce and if you have a small enough population size you don't have a large backup of reserves so over time if you get where these blue ones ultimately for a few generations are more successful reproducing just by chance it just so happens then you can rapidly get where this trait for red just disappears completely and once that allele is gone it's typically gone for good unless you have a you know rare mutation that somehow brings it back or unless we have some other event like migration that does so this one tends to make things lose alleles this tends to have an impact that whittles down the gene pool to be smaller and smaller so this would be considered a very negative effect over time you do not want to have a population experience genetic drift this is not normally like a positive way of evolving this is normally going to give you less options when you need to adapt because it's removing variation and you need that variation to already be there once some new selective pressure comes along if you don't have the proper variant then ultimately that can lead to extinction so this is not great and there's two general scenarios that can lead to genetic drift the first is where you have a large population that's successful and maybe it's gotten a little packed on the particular island you're on or maybe the particular coastline you're on and so some of the individuals decide that they're going to kind of try to find a new place and so you get where like a small group breaks away from the original and so it's small because it's this breakaway splinter group the original group still exists and they can still be a large group one that's not going to experience genetic drift but that small splinter population that's founding a new population is small enough that it will experience genetic drift the other way you can get this is the bottleneck effect and so this is one where kind of like if i tried to pour these out you'd have where there's this limiting area at the neck of the bottle where it kind of forces things to shrink down to a smaller size so it slows things down if you have something like a natural disaster occur you get where as you're pouring it so to speak a lot of them don't pour you know it blocks up here and so some get out but a lot stay in so essentially a natural disaster can be where we wipe out a large chunk of our big population so what we're left with now is only a smaller part of our original population because the rest of these died you know they died in the fire earthquake famine drought whatever and so our big population is now reduced due to this event that bottleneck event that shrank it down to a small population that will now be susceptible to genetic drift so as an example of this we have drastically reduced the population of cheetahs now in some cases there's enough cheetahs that are kind of around each other that they're probably still hanging in there okay but we do have some of these groups now where cheetahs still live but they're these small groups we don't have very many cheetahs there so you're essentially now getting these cheetahs that are just hemorrhaging a lot of their diversity which makes it much more difficult for them to survive long term this is why as a biologist we get so nervous when a population starts to get small in size it's not that they couldn't eventually have a bunch of children and start to build back up but by going down to a small number of individuals they've lost much of their genetic diversity which means if some other tragedy happens there's a good chance they won't have enough variation to get through it now the next thing we have is gene flow which really is just a fancy word for migration and this can have two general effects one of them is you could have a population let's just assume this population here was the original one and if you've got one individual or maybe a few that have a different allele and those individuals leave so let's assume this guy actually managed to fly and get to the other side of the mountain we could lose alleles we call this idea of somebody leaving immigration so emigrations when some individuals are exiting a population and this can ultimately lead to us losing alleles so that's kind of the bad way we don't want to lose alleles we want variation but then there's another type of variation that's good so this is like this blue guy here that manages to get across so we've now added this blue allele that was not there prior for this population b and so that would be due to immigration where you have individuals that are coming in i'm going to try to use the n for the i and the exit for the e so it kind of makes sense so they're coming in and so they're essentially adding alleles and this is very good because it helps us add to the diversity so once again if there's some new selective pressure we're more likely to have the proper allele that lets us get through that lets some of the population survive it and then repopulate so we don't go extinct non-random mating really focuses a lot on this idea of like sexual selection that females ultimately tend to have certain preferences for traits now some of these can be due to the sexual selection where it's more the male's fight for access to territory and the females prefer males that have territories they want to live in so you know the males fight most intensely over the best territories and therefore the best males you know the ones that seem to be the most able to survive even given this you know battle that they constantly have to fight or perhaps it's like deer where they've got horns they have to grow that they have to use the fight so they must have enough energy and have good genes to be able to grow those horns to be able to withstand those fights to defend that territory so the females then move into those good territories disproportionately so like more than the bad territories there might be a few women in the worst territories but not as many and so that means the males that control the good territories reproduce more you can also get regular old sexual selection where males look pretty and so you can have where they're chosen just because of that you can have things like inbreeding because those are the individuals around so you don't have a whole lot of choice there's things called assortative mating where you tend to prefer individuals that look like you but for lots of reasons people do not have organisms do not have an equal chance at reproductive success there's a whole bunch of stuff that goes on that make it where women are more likely to favor certain traits and so those traits will become more common non-random mating we've now got mutation now mutation is going to be these changes that can naturally occur especially when you're going through replication and to be very significant we'll say when you're going through replication of dna prior to meiosis so you're going to produce these gametes that have these particular mutated alleles or mutated genes that allow us to get new or modified traits now in many cases we've discussed these can be bad so these can be disadvantageous which means they tend to die out but occasionally as we said they can be good so they can allow us to get this new variation you know these new characteristics that did not exist prior the other piece i want to make sure i bring up with mutations like i need you to know these are critical because while they're oftentimes bad they allow us the one major thing that gives us brand new stuff you know gives us new characteristics that were not there whether it's new colors bigger size it could be modified structures where you've got more webbing in your fingers until eventually you can get like a bat wing but i want you to make sure you realize that these mutations will typically be small changes i don't want you to think that one mutation tends to be huge so for instance if you're going to try to fly i don't want you to think that you're suddenly going to get something that's like a regular squirrel that in one generation kind of poof becomes a flying squirrel that is able to glide long distances i don't want you to think that we had like a dinosaur that ultimately in one generation suddenly got these full-fledged wings and was able to be a bird so if you're doing something like flight you would have a small change that makes something that's more likely to just fall with style so it can fall and not die this can be critical if you're in the trees and being hunted you can either stay in the tree and get eaten or you can fall to your death if those are your two options you're removed from the gene pool but if you can fall and survive the fall and not get eaten you can now pass on this gene of falling with style so maybe you had a bit more webbing than most maybe you're a bit skinnier maybe you're a bit more aerodynamic or flatter but these small little changes you had made it where you just barely survived some falls maybe not even all the time but enough that it was significant and so now you pass on your genes more so now you got a group that's better at surviving these falls and eventually some of them start to have maybe some additional mutations or additional selection that makes them have a bit more webbing a bit better shape and so now they survive more consistently or maybe they start to glide forward a little bit better so they can land a little bit better and eventually over time we can get to a flying squirrel but it's bit by bit by bit not all in one big jump you're not going to see something like this where it's a grasshopper with a rabbit head i know you like to see a lot of people that talk about genetics where proof suddenly you're like half and half this does not happen you know you could have where maybe you'd get a grasshopper that has some little hair like extensions that it has on it you could get maybe where something has a slightly different looking eye but you're not going to suddenly get a rabbit eye on a grasshopper that would be tons and tons and tons of mutations you're not going to see it work that way and then lastly we've got the idea of natural selection which is going to focus primarily on this idea of survival but keep in mind the reason survival matters is because that then allows you to reproduce more this assumes kind of equal reproductive chances of those that make it to adulthood still we're kind of ignoring sexual selection but you have to survive to be able to reproduce and the individuals that survive to be able to reproduce are the ones that have the good genes for that particular environment as it is right now now there's three general ways we describe selective pressures affecting natural selection so i'm going to quick go over those now the first one we have up here is one where this is the norm so we've got this red line that represents like the original population where most individuals were kind of this middle color of these clams and then you had some that were like grayers some that were browner but we had this spectrum over time there can be selective pressures where the worst thing you can be is in the middle so the middle is the worst but if you're at either of the extremes you do better so we would call this disruptive or sometimes they call it diversifying selection and so this will favor both different phenotypes both extreme phenotypes over the middle phenotype this one is very good at eventually leading to speciation because we now start to get two different populations you know imagine if we were describing size with this you'd start to get a big population and a little population and i don't mean the actual size of the population i mean the size of the individuals in the population so you're essentially getting like you know dwarfs and you're getting like giants and so it's pretty easy to see that if that continues for long enough you could eventually get two completely separate populations that become their own species so this one's great for leading to a new production of species there's also this one here where the best individual is the one that's right in the middle so this is the ideal to be in this middle part we call this one stabilizing selection because both of the extremes are bad this is how in this case it's showing lizard tail working but this is also how baby weight works if you have too big of a baby it can cause complications with birth so especially in the past that would be a very bad thing having too small of a baby a premature baby typically cause problems with the baby and so the baby might die and so the best thing to be was rate in that middle ground probably like you know six to eight pounds that's an example stabilizing selection and then lastly you can have where the middle and one of the extremes are not good the best thing you can be is one extreme and so we call this directional selection because it favors things moving to look more one extreme so this is how we'd explain things like the giraffe where consistently it wasn't like we liked the small drafts and the big drafts it wasn't like we liked the middle drafts we liked just one extreme just the big drafts and so those individuals that were the tallest were able to get the most food so they could survive the best so they could reproduce the best so over time we saw giraffes getting taller and taller and taller as i start to wrap up natural selection i just want to reiterate one point a lot of people act as though evolution and natural selection is chance that it's random there are random aspects gene flow can be somewhat random mutations certainly can be random but natural selection itself is something that reliably occurs based on the environment that certain traits will survive and reproduce more this is not random the environment nature is essentially choosing who is going to survive and who's going to be able to reproduce more so their traits become more common so other parts of what we talked about can be random there is certainly some aspect of randomness during this whole process but the actual process of natural suction is not random and lastly we talked about this with the wings as i described it i want to make sure you guys realize we can get complex traits the idea of irreducible complexity is a straw man you can get very complex things like eyes flagella and wings that seem impossible to just go from and not having them to having them but you can get them bit by bit and we see this we have fossil and living elements that show us different stages of the eye from simple things where it's just an eye spot that tells light from dark all the way through a modern eye like ours and each of those represented something beneficial to the animal that possessed it you know even knowing light from dark is better than nothing at all you know knowing the direction of light is better than knowing nothing at all and it's better than just knowing if it's light or dark having a crappy image is better than just knowing the direction of light and so each of these stages can occur bit by bit and so over the course of evolution we can eventually get to something that's very very very very complex but we don't have to get there right away and every time people pick these characteristics that they say could not suddenly appear that could not ever be formed by natural selection we end up sitting down and saying well this is what we expect to find these in between transitional forms that are kind of working their way there and when we sit down and look for them sure enough guess what we find all these transitional forms that are you know starting out simple and working their way to a complex die starting out with a little structure and working its way up to a bacterial or eukaryotic flagella or starting out with just the basics of maybe a little bit of extra webbing or just skin and ultimately working their way up to some sort of like a wing that they can use for advanced gliding or that they can use for flying