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Lecture 7

7. Lecture Seven - September 29.docx

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University of Toronto Mississauga
Jessica Hawthorn

EVOLUTION III We were talking about Darwin. Darwin did not create the theory of evolution. It is an idea, a concept, and a reality which was recognized long before Darwin. Darwin came up with a mechanism for explaining how evolution actually occurs. As he travels on the beagle as the ship’s naturalist, he visits a lot of places. The Galapagos are a hotspot off the coast of Ecuador. As he goes around looking at plants, animals, and fossils, and he notices a couple of things. Islands have tortoises on them, very large ones. Darwin observes a couple of things about them. The presence of tortoises on islands in the middle of the ocean is weird. How did they get there? Darwin notices that there are differences in these tortoises. They are actually different species. Tortoises are primarily plant eaters. They’re herbivores. Darwin sees a connection between the anatomy of these turtles and the environment that they live in. Finches Darwin notices variation in the finches. They’re little brown birds. All of the finches in the Galapagos are related to South American finches, as per their features. The finches on these islands have different shaped beaks. Okay, here’s a question. When you’re having lunch, what are the primary things you use to consume your lunch? Your hands and your mouth. Now, imagine consuming your food with just your mouth. Birds have their forelimbs completely locked up for flight. Food is hence acquired directly through the beak. Beak shapes correspond to particular ecologies. Adaption: Darwin realizes that what he’s looking at are multiple, specialized adaptations. What is an adaptation? In terms of evolution, it is a feature of an organism that has evolved to function in a particular way of life. Pangolins and armadillos are both mammals, but the adaptations they exhibit have evolved independently. They develop two anti-predator mechanisms that converge along a similar mechanism and serve a similar function. We can see convergences all over the place in the biological record. Natural forces act on the anatomy and morphology of different animals to shape, independently, the same responses to the same environments. Darwin spends five years on the beagle and collects a massive amount of data. He spends the next 20 years trying to draw out a conclusive thesis from this data. He studies the embryological development in living animals and selective breeding of domesticated animals. At the early stages, we’re all very similar, even across different species. (See Professor’s notes for pictures) Selective breeding of domesticated animals: - Breeders decide on desired characteristics. - Only individuals with those characteristics are allowed to reproduce. - Eventually all offspring will have desired characteristics. - Darwin called this „artificial selection‟. Breeders decide the characteristics that they want and selectively breed these animals. After a certain amount of time, all the offspring will have the characteristics that you bred. We, as humans, can come up with new breeds of dogs in 10-20 years. There is a cat that is hairless. After enough selective breeding, the selectively bred animals will no longer be able to reproduce with members of their original species. Hence, they will become a species of their own. Natural Selection: this was the mechanism which Darwin came up with to explain how Evolution actually takes place. 1. Variation of heritable traits within populations of species. Populations of animals vary in the traits that they inherit from their parents. 2. Variation in traits is advantageous in competition for resources (food, mates, etc.) 3. In each generation, more offspring are produced than can survive. 4. Individuals with advantageous traits within population variation will leave more offspring, increasing the number of individuals possessing the advantageous traits in successive generations. In every population, there will be some selective advantage or disadvantage to this variation. If we line up everybody by height, there will be some sweet spot that will be really advantageous for acquiring food or mates, or whatever. There is always an excess of offspring produced as this contributes to the survival of the species. Remember Lamarckian Evolution. Lamarck argued that traits acquired during the life of an ancestor are passed on to descendants. Today, we know that the only stuff that gets passed on from one generation to the next is what is recorded in your DNA. If natural selective forces act such that they favour longer necks, then longer necked giraffes will survive and reproduce, thus increasing the number of offspring with long necks. Homology: “the same organ in different animals under every variety of form and function.” Homologous traits are
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