Bio1A03

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I All right.

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All right, we're gonna get started. OK. Uh, I'm gonna turn this up a little bit. Can you guys hear me clearly in the back? Yeah. OK perfect uh quick announcement coming from the Mac Bio Society so there's an undergrad led uh group uh of students, um, where they get together they share resources about biology programs and get to know one another, um, so they're actually gonna have their first formal um. Uh, events, um, happening Friday, January 31st, 6 p.m. um, if you'd like to get tickets for that, the QR code is there and I've also posted this on the A2L announcements page, um, so you can get the details, um, on there as well. All right. So jumping ahead to where we left off yesterday. OK, so just to reorient yourself, so we're talking about three of the greatest unifying ideas in biology. So today we're gonna complete the Life is Cellular, um, one of the theories, um, and then hopefully we'll get through life processes information. So then on Friday we can spend the whole day talking about evolution and then for the subsequent, uh, 5 weeks we will also continue to talk about evolution. OK. So we're going to talk about two competing hypotheses when it came to self theory, um, and so, um, rather than sort of pulling the group, um, I just want you to take a brief moment, um, to jot down the definition of a hypothesis because this is gonna be something that's gonna be important um for a lot of the activities we do as well as for testing purposes so make sure you know you're familiar with the definition of a hypothesis and how it be different from a theory which we covered yesterday. Um, and the textbook, uh, chapter 1.1 will give you the definition. OK, so a hypothesis is a testable statement that explains something observed. So it is uh based oftentimes on a single observation whereas a theory would be based on a bunch of observations that are all corroborating with one another to explain something a little bit more general. So that's how they how a a theory differs from a hypothesis. An experiment, which is another definition you should know, it allows researchers to test the effect of a factor on a particular phenomenon, something that you can measure. A prediction is a measurable or observable result that must be correct if a hypothesis is valid. So students, uh, often and and actually not just students, even scientists will sometimes use hypothesis and prediction interchangeably, but we're gonna actually spend a little bit of time talking about the distinction between those and why it matters for when we go and and start thinking about experimental design and setting up our experiments. OK, so One of the simplest ways to think about the distinction between a hypothesis and a prediction is if we formulate our hypothesis in a very specific um way. So if we formulate our hypothesis as X, so X could be some explanatory or independent variable that we might be manipulating in our experiment, for example. So X affects Y and Y would be something that's um it's the response. So it's a dependent variable. Something that you can observe and measure. So X affects Y. That is the format that we're gonna use for this course when it comes to uh um stating a hypothesis. So really, really important to ensure that it's different from the prediction which would be, for example, it could be X increases or decreases or reduces um why. So it's a direction, it's implying a direction um if the hypothesis were to be true. OK, so predictions imply direction, hypotheses do not imply direction. And predictions, um, Only come about if the hypothesis itself is valid. OK, so this is something we're gonna practice a lot with, um, in the next few slides as well as on Friday. So if it's not super clear what the distinction is right now, I'm hoping that it'll be quite clear after we get some practice. OK, so the two competing hypotheses, um, one that had been around, um, for quite some time up until the mid 1800s was, was this idea of spontaneous generation. So this was the um hypothesis that organisms could arise spontaneously under particular conditions and that bacteria and fungi which they wouldn't have actually known in the 1800s exactly what those were but those are the names we'd give them now. Those that spoil foods such as milk and wine would spring to life from nonliving materials so they just sort of spontaneously arise and then give um uh rise to um additional growth or or cell proliferation. So that was the prevailing paradigm what um individuals at that time would have thought occurred. Whereas cell theory was the challenging hypothesis, where all organisms are made of cells and all cells come from pre-existing cells. So those two statements, all organisms made of cells and all cells come from pre-existing cells. Those are two testable statements. Does anyone know who came up with the original cell theory and did one of the most um famous experiments on this? Uh, yeah, I see your hand. Sorry, Pastor, yeah. And we will talk about his experiment right now. So he um was making a hypothesis that would state cells arise from cells and cells do not arise by spontaneous generation. So it's sort of rejecting the idea that cells could just arise spontaneously from non-living material. OK, so here's a bit of a challenging question. It's OK if you um don't get it on your own. How could you rephrase Louis Pastor's hypothesis into uh into an XXY type of statement? So in this case it could be X is required for Y. So take a few moments here. You can you can chit chat amongst yourself for a minute or so just to see if you can try to rephrase this in the specific formula that I've given you for a hypothesis. All right. Hopefully you have a few ideas. Is there anyone who's willing to give uh a guess to or or their response of what you came up with? Yep. How many cells grow out of it. So X is the presence of pre-existing cells. Why is how many cells are gonna grow from that. Awesome. Did anyone else get something different? Or some variation of that. OK, awesome. Well, you nailed it so presence of preexisting cells um could lead to cell growth. Now it's totally fine if you said um cell proliferation or um further cells would arise from that, whatever sort of variation you put on that. But basically the important thing here is that we have our X, something that we could manipulate for example, and then why something we're measuring something observable. And then putting it into our formula for a hypothesis, then we can actually start to think about well how would we go about testing that hypothesis. So the hypothesis was stated would be the presence of pre-existing cells is required for self growth. The null hypothesis, so it's how you know that your uh hypothesis is formulated correctly is because you could often just put is not in front of the effects or is required um and then it makes sense and it's not implying a direction. So the null hypothesis would be the presence of pre-existing cells is not required for cell growth. The predictions that come out of this would be, so outcomes if the hypothesis were valid would be that cell growth will only be observed if preexisting cells already existed. Cell growth will be observed regardless, whereas the null hypothesis would state that cell growth will be observed regardless of whether preexisting cells. Already existed so this would if anything actually I would change the predictions to outcomes because these are the different outcomes that could possibly happen from the experiments um and one of them would support the hypothesis that you you um sell uh presence is required to get further cell proliferation. OK, so So we are thinking about how to formulate a hypothesis, thinking through the outcomes of an experiment that would allow us to validate that hypothesis or not. But what about going and testing that experiment? Yeah, I, I see it in there.

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Characters between these type of pieces in the prediction because I don't.

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Yeah, so in this case, the, the prediction is not implying direction, but it is providing an outcome. So cell growth will only be observed if preexisting cells already existed. So it's stating an outcome of the hypothesis that, so the testable statement that the presence of pre-existing cells is required for Cell growth. If that was valid, then cell growth will only be seen if there were cells, um, there. So it's an implying uh uh outcome of the experiment, whereas the null hypothesis is the second statement. So cell growth will be observed regardless of whether preexisting uh cells already existed. No worries. Again, when we get into more examples of this, um, in some instances predictions will imply direction but not in all cases and in this case, a prediction is just the valid um outcome of the supported hypothesis. OK, so what Louis Pasteur did was a fairly elegant experiment where he took two types of flasks, a straight neck and a swan neck flask. And so you can kind of see if you can see my cursor here. So in one case, we have this sort of um little bit coming off of the flask opening and this one is just straight. Um, he added broth to both that had um been sterilized. So boiling kills all the microbes, therefore sterilizing both. So they are treated both the exact same way. But then in one of them he he he's just allowing those to kind of sit um and um. You know, for, uh, either dust particles or whatever to um interact with the flask. So in one case, dust particles carrying microbes could enter the straight neck flask, but not the swan neck flask because they would actually get caught in the opening. So those cells that are just in the environment would not be able to um get into the broth. So basically the swan neck is excluding the presence of pre-existing cells, whereas the straight neck is not. Um, at the end of the experiment, um, it, he found that in one condition that the broth remained clear and sterile, so no microbes appeared. In the other, uh, flask, broth became cloudy because of the growth of microbes. OK, so based on the results from this experiment, would the null hypothesis be rejected? Why or why not? So who would say that the null hypothesis would be rejected based on the results of this experiment, just with a show of hands. OK, and who would say that it would not be rejected. In other words, that the hypothesis is invalid. Mm, OK. So I think in this case it was pretty clear that the presence of pre-existing cells, which would have been found in the straight net class, so the microbes would have colonized and then you got further growth which is shown by the cloudy color. So often the cloudiness of broth indicates how many cells have proliferated, so that's something you could measure. Um, and in this case it was only in that condition in which preexisting cells had been present in which that cell growth had been observed so it's, it's validating or supporting the hypothesis. Also just a side note, we'd never prove hypotheses we either have support for them or not, um, and in this case though, we would be able to reject our null hypothesis. Which was stated previously in the previous slide that cell growth would be observed regardless of whether preexisting cells already existed. So in other words, it's pretty conclusive evidence that the uh presence of cells were required for that cell growth to be seen, which, uh, suggests that his hypothesis is well supported. And of course, nowadays we have yet to do an experiment where this has not been shown over and over again. So it's fairly robust experiment. Any questions on that before we go through a quick recap? Yep. Hm. That's a good question, um. Because there's no like. I think the the more evidence you have for something, especially when it's, you know, collected independently for example by different research researchers there we can build a consensus um and then maybe that could be could could be accepted as fact, um, but in some instances it's really hard to sort of delineate like how many experiments do we need in order to say that something is a fact or not but we could say that a hypothesis is is really well supported or um. Has been around for quite some time and we haven't been able to reject it but the goal is always in science to be able to falsify um uh uh a experiment or a test but um in this case um it's it seems to be you know now that we also understand the mechanism of that which. Also corroborates why he got the outcome that he did. It all kind of pieces together that this is sort of accepted as fact now. Does that answer your question? So yeah, not a very straightforward answer, but, um, impressing upon you that when we call something a fact, there's no like specific criteria we're using for that. OK, so really quick, uh, recap here, uh, what does it mean to say that something is alive? There is no single well accepted definition of life. Instead, we can identify common characteristics that most organisms share, but nonetheless, there's always gonna be exceptions to those rules. So we could consider some organisms living even if they didn't have one of the three, characteristics, for example. And then what we're introducing now is three of the most influential unifying ideas in biology cell theory, chromosome theory of inheritance, and theory of evolution. And that we spend a bit of time talking about life emerging from cells. So cell theory identified the fundamental structural unit common to all life. OK, so we're going to get into chromosome theory of inheritance again. I'm being quite brief on this topic because a lot of it should be reviewed from, uh, potentially a course that you've already done, um, but I'm trying to kind of take you from there to evolution so you can kind of see the connection between them. So we're asking the question how is hereditary information transmitted from one generation to the next? So the chromosome theory of inheritance was proposed in 1902 by Walter Sutton and Theodore Bovary. One thing I want to point out is that I won't be testing you on dates or names, so don't spend too much time completely memorizing this, but nonetheless, I still think it's really important to think. About how the ideas that I'm presenting in class when they came to be um and how long they've been around for because that actually gives us a lot of information about how robust some of these hypotheses are um so again don't memorize the the names and dates but nonetheless I'm gonna include them because I think they're still important for you to know. Um, hereditary or genetic information is encoded in genes, so that would be a definition that you would want to be familiar with. Genes are units located on chromosomes and in the 1950s, um, it was discovered that chromosomes are molecules of uh deoxyribonucleic acid or DNA. Um, and DNA is the hereditary material. So actually before we even knew anything about the molecular makeup of DNA, um, hereditary material was sort of thought of, um, almost as like a philosophical theory about how things are transmitted, how information is transmitted, but nonetheless, in the 1950s is only when we actually understood the mechanism of that and that's not that long ago. So genes are segments of DNA that code for sell products, um, and I'm going through this pretty quickly because it's proportional to, you know, how much time you should be reviewing this material, but nonetheless, it's important to set up. So each strand of a double helix, um, is made up of 4 building blocks so we have A, T, C, and G. And the sequence of this code um is like letters in a word um so again if you're gonna take genetics or another course you're gonna be very familiar with um how these code for proteins like the process in which that happens um so DNA carries or encodes information that's needed for an organism's growth and reproduction. The two strands of the double helix are held together by connections between the blocks. So it's a very specific pairing. So A pairs with T and then C pairs with G, and then this allows this pairing allows the DNA to be copied. And it preserves the DNA, uh, the information encoded in the DNA. So think about copying, um, right? So we're actually, if we're going to replicate, if the cell is going to replicate, all of the DNA has to be copied with some degree of fidelity. Um, James Watson and Francis Crick, along with Rosalind Franklin proposed that DNA is a double stranded helix. So this was again something that we didn't actually know about, um, for quite some time until around the 1950s or so, and I did include a video on the A2L all about the double helix and it's, um, discovery on A2L, yeah. OK, so here is where I want to spend a bit more time really starting to think through why DNA matters when we talk about evolution because maybe for some of you that might be a very obvious leap, but um it's important that we spell it out and take some time. So genes and DNA code for information necessary to produce a functional product often a protein. And then DNA is inscribed to RNA um to uh RNA message, and then the RNA message can then be translated to a protein. So the central dogma is sort of describing this process in which genes are encoding information, the DNA is transcribed into RNA first and then RNA is then translated into a protein. So think of that flow of information. And then at the end the outcome would be some sort of outward appearance of the organism. Oftentimes there are many of course functions that you wouldn't see in outward appearance but in a lot of the traits that we're gonna talk about when we talk about evolution, it's gonna be traits that um you can measure, you could observe, you can um see if you're studying these organisms. So DNA is copied to pass genetic information from cell to cell or from one organism to its offspring. And remarkably, copying DNA is highly accurate. Um, but nonetheless, mistakes are made at some, uh, degree of probability. So the big question, and then this is why when we think about evolution that's so important is what happens when a mistake is made? What is the consequence of that? Um, in some instances, uh, a change or, um, maybe it could be what we call a single nucleotide polymorphism that I'll talk a little bit about in a few weeks' time. So you could have a small change that could potentially lead to changes in proteins. And that could impact the outward appearance of organism because it's a product of protein. So in other words, it can actually impact the traits that an organism is displaying. So it could be morphological, physiological, behavioral. DNA sequence changes may cause changes in outward appearance. And so the question then is how does this central dogma, so this flow of information help us understand how mutations so those changes in the DNA can result in disease? So this is something where you wanna think through in terms of that flow of information um and understanding how mutations. Actually relate to outcomes such as disease so I'm not gonna uh take this up as a group um today but it is something that you might want to um highlight in your notes is something that you should start thinking about so then if you were to ask be asked this on a short answer question for example on an exam you might have a response for it. OK, so really quick, um, review. Um, life processes information. So this is one of the three, unifying biological theories that we've been talking about. The chromosome theory of inheritance states that genes are located on chromosomes. Chromosomes consist of a molecule of DNA, which is the hereditary uh material, and genes are located on chromosomes that consists of specific segments of DNA, um, coding for products in the cell, and then the flow of information from DNA to RNA is called the central dogma. So here's the critical point that I'm trying to build up to that imperfect replication, also known as mutation, which will be a definition we'll go through quite a bit in um a couple of weeks' time, provides the source of heritable variation in traits. So the thing that can be passed. On from generation to generation is found in the DNA and that this process this imperfect replication is the source that fuels evolution we have to be able to have heritable variation in traits in order for evolution to occur OK. All right, so I'm gonna check how we're doing for time here. Which is awesome because that means we can spend a lot of time on Friday with our activities. So in the next few slides I'm going to give you um sort of the introduction to evolution. It took us a lecture and a half to get here, um, but again just kind of setting up some of the basic terminology, the concept itself, um, and then we're gonna spend a lot of time getting into the nitty gritty from here on in, and the question that we're asking is where do organisms come from? Um, section 1.4 in the textbook will introduce a lot of the concepts here. OK, so this one we are going to take a little bit of time to chat about. So if a non biology major friend, also many of you might not have declared your majors yet, so you might be in this category, um, if someone had asked you what is evolution, what would your initial response be? So gut reaction um so what I'm gonna do is take a couple of minutes this time um and you can chit chat with someone next to you or if you prefer just sort of writing your own response to this, um, down you can do that um and then I'll, uh, solicit a few responses from you in a few minutes. All right. OK. So If there are any brave volunteers, what did you come up with? Yeah. Some changes over a long period of time. Awesome. Changes in in what? Just a little bit more specific. OK, OK, so, uh, changes in, in organisms, um, and their traits, um, over a long period of time, awesome. Other responses. I see a hand up in the back. Adaptation and then. What what would be the definition of that? OK, so I think I heard the last part of what you said, but basically there's some change in the environment and it could be sort of traits that are, uh, responding to that and maybe you, uh, have a more favorable outcome in that environment. Did I capture what you said or OK good awesome. Any other responses? Yeah. Randomly occurring mutations that are passed down in advance. Species are more likely to survive to age. Awesome. OK, so you're, you're bringing in sort of the idea of mutation, so the heritable, uh, source of variation, um, that, uh, is passed down from generation to generation, um, due to it being, um, potentially beneficial and increasing survival. Awesome. So basically I've done my job. I can go home now. I don't need to talk about evolution um, those are excellent responses. Did anyone get something slightly different or um that isn't kind of encompassed with the responses that we've had so far? No, OK, so I think we have an excellent foundation then, um, so what I'm gonna do is instead of giving you the response because I hope that the response will be clear to you as we, uh, talk about evolution in more detail. I'm gonna actually back up a little bit and talking again about the importance of history and when ideas kind of came about and then how sort of there's this almost evolution of thought and how there was a challenging view um and uh basically how. How the scientific community eventually adopted that new challenging view so um when it comes to the way we think about how organisms or or where do they come from essentially one of the prevailing paradigms um for quite some time of uh human evolution, um, would be considered special creation which is also uh another uh synonym for that is natural theology. And actually there's uh a lot of evolutionary biologists, um, and in Darwin's time at least, Darwin was very uh influenced and inspired by a lot of the original writing of, uh, someone who would consider themselves to be the prominent person in natural theology. So a lot of the ideas that Darwin had were inspired by the prevailing paradigm at the time. So not to say that when we switch to a different paradigm that we're sort of getting rid of all the ideas from the original one that's usually not what happens, but the claims that the special creation paradigm were stating uh the testable claims would be that all species were created separately and therefore are unrelated to one another. That each species is unchanging and there is little variation within each. Species being a distinct identifiable type of organism, we're gonna talk a lot more about species in week 4. But just a quick definition. OK. So those are two claims really important that you are familiar with those claims. Again, they're testable statements because we can go and verify them. So then there were some challenges to that prevailing paradigm and they came about in very different ways from different people, um, one in particular, a group of individuals, the early paleontologists such as Mary Anning, um, so this would be like the end of the 1800s, mid 1800s or end of 1700s, mid 1800s. Discovered fossils for life forms that no longer existed so for organisms that um no one had ever seen before. So of course that would sort of go against the claim that species um basically if species could go extinct, it was met with a lot of resistance because why would they be created if they're just gonna be snuffed out essentially. Um, actually this book that I've put, um, a link to on A2L, it's, it is a I guess a historical fiction, so there's definitely a lot of the details aren't completely historically accurate, but nonetheless it it does talk about Mary Anning and sort of her um influence in in the field of paleontology, and it's a really fun read if you haven't read it already. OK, so skipping ahead a few years after Mary Anning, so this is 1858, Charles Darwin and Alfred Russell Wallace made two claims regarding the natural world that almost stand in complete opposition to that the prevailing paradigm at the time. They made the claim that species are related by common ancestry, so they're not completely separate, distinct, unrelated. They're all related through common ancestry. And that characteristics of species can be modified from generation to generation, and this is also known as descent with modification so that means there are changes um within species that can happen over time which um one individual over here presented as one of the definitions of evolution. OK. So, so these are again testable claims, right? Things that you can go out and make some observations and see whether these claims are validated or not and how do they compare to the prevailing paradigm at the time. So when we talk about species changing over time we often think of that in terms of microevolution, uh, which we're gonna spend uh all of next week really delving into whereas when we talk about species splitting and diverging, that's often referred to as macroevolution so that's when we get into the concept of speciation, um, and we'll talk about that in the 3rd week. Um, so just a couple of definitions off the top of, of, uh, the bat, um, where we will be talking more about each in the coming weeks. OK, so then what is evolution? So this is the definition that we're going to use for the purposes of the course, although I, I, I believe that you all presented a a nice um eloquent definition of it as well. So it's a change in the characteristics of a population over time. It means that species are related to one another and can change through time so there is a secondary part to this that common ancestry is sort of critical for evolution to be true, um, and that it suggests that species are changing over time so species forming populations and within the populations those characteristics are changing from one generation to the next. OK well we we have population in the definition so we have to make sure we know what uh uh the definition of population is um so it is a group of individuals of the same species living in the same area at the same time that's a really good definition to be familiar with. OK, so how does evolution occur? So we're talking about this sort of, you know, theoretical concept, but what is the mechanism of evolution? And there are several, um, but you can kind of categorize them into adaptive mechanisms uh one of the students mentioned adaptation, um, so there could be adaptive uh methods and, and we also refer to this as selection, um, chapter 20.4 of the textbook, um, focuses on selection and we will talk a lot about that next week. But then I want to uh present right off the top of the bat that there are non-adaptive mechanisms that are just as or in some instances more important for generating evolution. So genetic drift, gene flow, mutation, non-random mating, and we'll get into all of those mechanisms in chapter 20.5. So that'll be in a couple of weeks' time. But let's just start talking about uh um adaptive forms of uh evolution because that is where Darwin comes back. So linking back to Darwin and Wallace. So Darham wasn't the first to challenge the idea that species were unchanging, but he was the first to amass a huge amount of data or evidence to back it up. So it wasn't even just based on a single observation, but many, many observations that he had the luxury of going out onto a boat for years at a time, um, and actually, um, you know, looking at different species and characterizing them. So together with Wallace, um, Darwin and Wallace proposed the most famous mode of evolution, natural selection. Again, it's not the only mode, but it's the one that we're gonna spend a lot of time on. OK, so we're gonna talk about two conditions in which natural selection, um, it is contingent on. So these must be met for natural selection to occur in a population. The first is that individuals must vary in traits that are heritable so that the characteristics can be passed on. So the information, the DNA that gives rise to those characteristics must be able to be passed on from generation to generation. So there is some sort of genetic basis. For the traits that we're talking about, so that's the first rule, or condition. The second is that in a particular environment certain versions of those heritable traits help individuals reproduce more than other versions. So I think actually a student already alluded to this, so it's. You know, natural selection and when we talk about fitness it's not about being the biggest and strongest it's about the fit of a trait to a particular environment and environments change, right? So, so in a particular environment it's the heritable variations and traits that actually help individuals reproduce more than others um and those are the ones that are gonna be more likely to be passed on from one generation to the next. OK, so these are gonna be critical, um, to be able to, for example, if I were to give you a scenario with some information, um, and I asked you is, is, uh, there evidence of natural selection, you should be able to think through the two conditions that are met and see whether there's enough information to address that. OK, so a couple of more points here. So if certain heritable traits lead to increased success in producing offspring, then these traits become more common in the population over time. So think about it this way if there's only individuals that have, let's say, um, large feet, I'm totally making this up, large feet, um, in a particular environment it was those individuals that were able to produce more offspring contributing offspring to the next generation, those uh. Offspring are gonna be more likely to also have large feet because they inherited um the traits from their parents. OK, so it's really occurring on the population scale. It's the proportion of individuals in the population that is changing from one generation to the next. So rather than it being at the individual level scale, we could think of many, many traits that change at an individual level scale. My hair color gets a little bit lighter in the summer, for example, or we grow or you know, there's other sorts of things that might happen at the individual level, but that in and of itself is not evolution, um, whereas changes that occur at a population scale, the proportion of individuals with particular traits that changes from one generation to the next and that would be considered evolution. Natural selection acts on individuals because individuals that have those traits are either benefited more by them or less, whereas evolutionary change occurs in populations. This, I think I just remembering back all the way to when I was an undergrad was a distinction that took a while for me to get. Some of you might already be there, um, but thinking about evolution occurring on a population scale versus individual scale took me a little bit of time to grapple with. So if you're also kind of in the same boat, I'm really hoping that we're gonna set up a lot of different examples, making the distinction between these things so that it becomes more and more clear. The last point is that speciation occurs when populations diverge to form new species, um, so what we're gonna be really focused on is sort of the steps before speciation, um, and then we're going to talk more about speciation in in a few weeks' time. OK, couple of other important definitions. So fitness, it's the ability of an individual to produce offspring, and individuals with high fitness produce many surviving offspring, whereas those with low fitness produce fewer surviving offspring. Adaptation, very important definition. It's a heritable trait, so it has some genetic basis that increases the fitness of an individual in a particular environment. So I'm taking the time to verbalize these definitions because they're gonna be extremely important. OK. So the next, uh, sort of, uh, example I'm gonna go through is setting up sort of a scenario and then we get to think about whether we have evidence of natural selection occurring or whether there's an adaptation involved. So before I get into that, I just want to pause for a quick second to check in with everyone about the definitions I presented. Is there anything that you just have a sort of a quick question about, um, or want me to clarify before we get into the example? No. OK. OK, so the example that I'm gonna start with, um, is one of the more famous ones from Darwin's notes when he was, um, sort of traveling around and stared at a bunch of organisms, finches being one group. So the finch is on the Galapagos Islands. Um, one thing that he observed was that there's quite a bit of variation in beak size and shape, and this image here just kind of shows you visually what that looks like. So some of these with really sort of almost shorter like more stout beaks, more robust, others with longer pointier beaks. You also noticed that when rainfall became consistent, so when there was constant rainfall, that small soft seeds became more abundant in the environment. So there was this change in the environmental conditions such that the food type of the birds that was available was predominantly these small soft seeds. OK, so environmental change, uh, paired with standing variation, we already had variation in beak shape. What happened as a result of this consistent rainfall was that there was this observed shift in the proportion of finches in the population with small pointed beaks, OK, so maybe before there would have been like, I don't know 60% of the population. Had a different beak type maybe 40 had the small uh pointed beak, but then after this long period of rainfall, when you check to see how many individuals had small, uh, pointed beaks, it was a greater proportion, so something like went up to 60 or 70%. So the question I want to ask you, and you have to think back to the two conditions of natural selection, is whether small or pointed beaks are an adaptation to prolonged rainfall. How would you be able to test this? So think about what you'd have to verify or validate in order to say that this uh small pointed beak, um, is an adaptation to rainfall. I'll give you a couple of seconds. You could either jot it down or just quickly chat, um, and then we'll take it up as a group. All right. So I'm gonna check in. So what were some uh responses that you got to

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this question? Anyone on this side. Yep. And Oh, that's that's an excellent um sort of way

SPEAKER 1

of testing that question. So just to reiterate it's also so I'm picking it up on the uh recording so the idea was to look to see um the same species of fish but in different geographical locations where you might have more or less rainfall to see whether that same trend occurs where you get the more individuals with small. Pointed beaks when there's consistent rainfall is that capturing what you said? Awesome. And if that were to be found across a bunch of different regions, it, it probably would be, you know, good support that, um, small pointed beaks might be an adaptation. What are some other, uh, things that we want to verify? Yep, movement as well so that distinct and you could really observe. So really defining where the population is, right? is that what you're kind of getting at, um, and so being able to delineate sort of where the populations are moving and how they're interacting with the environment, is that kind of capturing that that would be important for sure, yeah. Yeah, so you'd actually have to make sure that the proportion has increased, um, after the rainfall. Absolutely, yep. So you'd have to satisfy one of the two conditions. This is what I believe you're saying, where you have to be able to see that the individuals with that trait are actually surviving and reproducing more than the ones that aren't. So there has to be some sort of fitness advantage to possessing that trait. Awesome. There's one other condition that we would also need to validate in order to say that small pointed beaks were an adaptation. Is anyone, uh, yep. It has to be heritable. So there, so for example, like so the proportion of individuals might have small pointed beaks, but if it's not heritable, none of the offspring of those individuals are likely to have small pointed beaks so there will be some sort of random number, but you won't see that proportion going up. So there has to be some sort of heritable basis, some sort of. Which we would now call genetic basis because we understand the mechanism. There has to be some genetic basis that gives rise to small pointed beaks as well. Those would be the two conditions fitness and heritability. Awesome, so we're gonna, uh, stop it there for today, um, and then we'll pick it up on Friday and we'll get into an activity.

SPEAKER 0

You Uh, when you talk about like natural selection, the trait become more common in the population over time, it doesn't have to do with like the parents of the. The how they because they have the trait they're able to reproduce more either because of the environment or I know like we like peacock the. like a. It's more Latinos that one way they're most likely to. In terms of meeting the That would be an example actually you would call that sexual. OK, and what you like. how many generations of that has to be there. That's such a good question and something that will get to mathematic. Evolution, or sorry, sometimes natural section lead to evolutionary change in a single generation. Sometimes, sometimes it takes many, many generations. So you said to uh think about the question about. Oh, you told us to think about the about biology. Yeah. So I guess how much.

SPEAKER 1

So I'm assuming first of all that maybe some students have taken that course, but it's not. So yeah, so any of the material that I'm presenting in lecture, for example, to see like that would all

SPEAKER 0

be like legit to ask a question about, but none of the actual information. We. Yeah.

SPEAKER 1

Perfect. Yeah, anything in the orange boxes, extra resources, that's for

SPEAKER 0

personal. Where are you? You know it's just heart rhythm rhythm, it might take me a few. It's something that we're gonna go back. It essentially are we getting at the fact that. Like