PROBLEM SET 1 PDF

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University of California, Santa Barbara *

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00174

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Anthropology

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Dec 6, 2023

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Anthropology 5 Problem Set # 1 Fall 2023 1. To answer these questions you will first need to watch the short video called Evolution of coat color in pocket mice (in Week 2, on the course website). A. As a result of geologic events, what was once a single population of pocket mice now find themselves living in two adjacent but different habitats. Mice in both habitats are often eaten by visually hunting predators. In the face of that predation, what role does coat color (fur color) play in a mouse’s survival? Explain. Coat color plays a crucial role in the survival of the mice in either of the habitats. For instance in a habitat where there is dark colored rocks , mice with dark fur will have an advantage to hide/blend in from their predators. While in contrast of that , habitats with light colored rocks , mice with light colored fur will adapt to their environment and that will help them hide/blend in to avoid their predators. B. Can you interpret your answer to 1A as an example of natural selection? Explain. N atural selection is the process by which traits that help with an advantage of survival and reproduction, which will help become more common in generations to come.mFor instance because these mines have the ability to match their habitats , they now have a better chance of surviving their predators , which will then lead them to reproduce . N ow as a result of this their will be increases of their populations and fur colors which will explain natural selection. C. Do genes affect coat color in these mice, and does that matter to your answer to 1B? Explain. I believe that yes indeed genes affect coat color which will then impact by other answer. For instance the difference in color that already lays between the dark and light mice is already due to genetic mutations. N ow certain mutations can lead to more differences in fur color making it a wider wage , in pigmentation. This helps different mice that are living in different habitats which is a genetic mutation . D. Traits change over evolutionary time and thus it is useful to be able to talk about what came first and what (changes) came later. For any given case, the ancestral condition (also called the primitive condition) is what came first. What do you think the ancestral (primitive) coat color was in these mice, and what change came later? What makes you think that was the order? I think that the primitive condition or ancestral color coat that came first was not either dark or light but neutral . Then change came over time as this those who were closer in color to their habitat survived , their population thrived leaving only darker and lighter mice. E. This change (from one coat color to another) happened “convergently” across the desert southwest. “Convergently” means that the same change happened multiple times, in different populations. What is the evidence that it happened multiple times? There are actually two separate kinds of evidence; please mention both. The two pieces of evidence of this phenomenon, I believe is Geographic Distribution and Genetic Variation . For instance when it comes to geographic distribution , dark and light miles cary through the divergent regions where the lava flows , as the video mentions “ different lava flows are location miles apart , yet they all still have mice with dark fur that matched their environment. This shows that even with differences in geographic separation ,adaptation can still occur where their survival is possible. As for Genetic Variation , researcher Micheal N achman had studied that genetic basis of coat color in mice from different lava flows and found that genetic mutations responsible for dark fur in these populations were different . But although they were different they still have the same adaptive outcome , of adapting to their local environment . F. All of the mice, regardless of which habitat they live in, have white bellies. Why did they evolve white bellies? A full answer would mention two ideas. I think that N atural selection is a factor in this evolution because although mice needed different coat colors to mater their respective habitats , this consistence may offer some type of protection.A white belly can help the mice when it is viewed from a different angle due to the outline making it less visible. Another piece of evidence can be that their wasn’t full genetic change but minimal

genetic alterations, this is because they really achieved only camouflage on the top side , this is because they are more visible to predators from that angle. So keeping a white belly minimizes the genetic alterations. 2. Selection changes traits until they reach the optimum (ideal) value. For example, if trait X is too small (given the prevailing environment), selection disfavors any mutations that decrease the size of trait X and favors any mutations the increase the size of trait X, until trait X reaches the optimum. I’m going to suggest that virtually every trait in every species has an optimum and that selection is always pushing towards that optimum; or stabilizing that optimum, once it is reached. A. We said how selection will work when trait X is below the optimum (too small). How will selection work if trait X is above the optimum (too large)? When trait X is above the optimum, selection will work to reduce the traits size. For instance , individuals with a larger trait X may experience some disadvantages , like reduced mobility . This is because selection is more likely to favor mutations that decrease the size of X as it approaches the optimum. B. And how will selection work once trait X reaches the optimum? Once the trait X reaches the optimum , selection will more than likely act to maintain that ideal value. As known that individuals with trait x close to the optimum will have the highest fitness because they will be able to adapt more to their environment. 3. Let’s consider a human trait that could be too big or too small, birth weight (the amount a woman grows her baby before she gives birth to it). Assume that birth weight is influenced by genes (it is, e.g., by genes that affect the flow of nutrients to the fetus during gestation). For questions 3A-C try to answer in terms of conditions during the long phase of human evolution before modern medicine (99.95% of the time our species has existed!). A. What might have been harmful to fitness about being too small at birth? When being to small at birth it could be harmful to the fitness for several reasons. To begin smaller babies are known to have a higher risk of not surviving infancy or even childhood because they are more vulnerable to diseases. Futhermore, even if these children do reach adulthood , it is also known they they can still face development and health challenged. B. What might have been harmful to fitness about being too big at birth? As if a baby was to big at birth , I think it can also be a harm to fitness as larger babies have a higher risk of maternal health , which can possibly lead to maternal mortality . C. What would have been the joint effect of these two selection pressures? The joint effect of these two selections pressures would likely be in favor of a weight that is a balance of the risk of it being to small or the risk of it being to big. This is because the balance will further the changes of both the infant and the mother being able to survive and continue to reproduce . D. Now let’s think about the present. Two medical services have become much more widely available in the last 100 years: Cesarean section and Neonatal Intensive Care Units. What does each service do? Given that, how might Cesarean section and Neonatal Intensive Care Units be changing how selection is operating on human birth weight. As for the present , that now changes how selection operates on human birth weight. That is because Cesarean sections allow for a safe delivery of larger babies , that maybe wouldn’t have been safe to have during natural birth. Because of this their isn’t really this pressure against larger babies . As for the advancement of N ICUs , they now provide better medical care for children to are premature , now increasing their chance at survival and reducing the stress of low baby weight. Therefore, these medical advancements have changed human evolution history as their isn’t this pressure for a “perfect” baby. 4. Let’s consider another example, this one from Chapter 2 in your Human Evolution textbook. In the second lizard study (pages 21-22 of your textbook) you learned that some lizards belonging to the species Anolis carolinensis have lately had to deal with new competitors belonging to a related species, Anolis sagrei .

A. Populations of A. carolinensis that were invaded by A. sagrei (but not those that were not invaded) show certain phenotypic changes: What are those changes? When invaded the changes included longer limbs and larger toe pads B. What were the selection pressures arising out of competing with A. sagrei that caused these phenotypic changes in A. carolinensis ? The selection pressures that arose was that longer limbs and larger toe pads had the advantage of climbing and accessing different areas of their habitat , which allowed carolinensis to be able to compete more with sagrei for resources and food . C. What is the difference between evolution and development? Evolution is the change of frequency of genes in a population across generations a response to pressures of the environment . While development is the changing expression of a single, fixed genotype over the lifetime of the that one individual , usually when something grows from a fertilized egg to a mature organism . D. All traits have both an evolutionary basis and a developmental basis; but a particular change can either be the result of evolution or the result of development. Consider the critical experiment described on page 22 of your textbook. Does this experiment suggest that the change you described in your answer to 4A was a developmental change or an evolutionary change. How can you tell? I think the the experiment suggest that carolinensis are more than likely due to evolution than than development . This is because when the baby lizards were raised in a control setting without sager around , they still showed the same changes. This can suggest that they changes are not a result to how they grow on their own but passed down by genetics .

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