FSU PCB 4674 - Lecture 1: Evolution and Natural Selection

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Lecture 1: Evolution and Natural Selection:What is the precise distinction between evolution and natural selection?- Natural selection acts on individuals, but if there is an evolutionary response, thenthe response is seen in the population as a whole. - If natural selection is acting on individuals, the population will only evolve if the trait is passed down to offspring.Evolution: Darwin is considered the founder of evolution even though he was not the very first person to think about it, but he was the first to synthesize the ideas into one cohesive idea- Darwin’s Five Theories – part of the history of evolution and its ideological development1. Evolution has happened2. All life on earth has a common ancestor – he did not have a lot of evidence for this at the time.3. Evolutionary change is gradual – he made a very strong case for this theory, however he may have overstated his case for this because we now know that someevolution changes can be rather fast.4. Natural selection is the primary agent causing evolutionary change – he proposed this as the mechanism, or force, which causes evolution to happen. Remember, he was not the first to propose natural selection.5. Evolutionary change involves both changes and a process of splitting – this was his most unique and important observation. This theory explains how all of the evolutionary organisms developed and got there.Questions:What are the evolutionary forces?Can there be genotypic change without phenotypic change?If there is phenotypic change without genotypic change is that considered evolution?Artificial selection: the process by which humans breed other animals and plants for particular traits. The greatest example of this is dog breeding and the many different types of dogs that exist today due to selective breeding. Another example is how corn was artificially selected from its not so useful ancestor, maize, to be the cash producing crop that it is today. Betta fish are another example.Natural Selection: The association between a phenotype and fitness of these individuals- First evolutionary force discoveredo In order for natural selection to be considered a driving force for evolution, it is required that the trait is passed on through genes, meaning it is inherited by offspring. If this is not the case, natural selection can still occur but it does not drive evolution because it will not affect the population.- Independently discovered multiple times in the 19th century- Part of Darwin’s comprehensive view of evolutiono He viewed evolution as a historical, ecological, and ‘genetical’ concept Historical: Evolution is a branching pattern through time reflectingthe phylogeny of life Ecological: The idea of natural selection and how phenotypes reactin an environment ‘Genetical’: He believed that a trait needed to be passed down to offspring in order to be considered natural selection as a driving force for evolution- In quotes because at the time no one knew about genes. It was recognized that traits were passed down to offspring, but no specifics were understood. The first person to describe genes was Mendel, who was working in the same general time period as Darwin. - Previous belief was “blending inheritance,” in which parents’ genes are averaged, and that is what gets passed on. The problem with this, from Darwin’s perspective, wasthat this does away with his very first idea in the theory of natural selection, which is that there must be variation within a population. Whenever something “blends,” you never get the original phenotype back.- Scientifically controversial until the 1920’s- Intelligent Design and Natural Selection For natural selection to occur as a driving force for evolution, there must be:1. Variation among individuals2. The variation MUST be inherited- A study that demonstrates this part of his theory of natural selection is with finch beak depth in parents and offspring. - We have established that there is a variation in the beak depths of finches in this population, and we must prove that this is inherited in order to be a driving force for evolution.-- The regression line graph of beak depth inheritance estimates the heritability of the trait, basically estimates the proportion of variation of this phenotype that is due to genes. It is showing that there is definitely a link between the two, because of the strong positive correlation. It appears that the trait is passed on.- We must consider some factors that could complicate these results: the amount of parental care could be influential to beak depth. Because of this factor, among others, we do not know how much variation is due to genes. (Read box on page 84-85!!!!)3. More individuals are born than will survive to reproduce 4. Some variants will survive and reproduce at higher rates than others – variation infitness and association with phenotype- A study that demonstrates this part of his theory of natural selection is the survival of finches that were born in 1976, the year before the drought of 1977, and how this correlated with the beak depths of the population as well as the variants that were then born after the massive drought in 1978. --- Birds that survived mostly had larger beak depths. A lot of the birds died largely because they did not have enough food. - By looking at seed abundance during the drought, it plummeted, but then spiked back up after the drought. The green graph shows variations in seed types. Once the drought started, large hard seeds were the only food type that was largely available, and therefore the only birds that survived to reproduce after the drought were the ones with beaks that were able to crack them. Whatcaused selection was loss of food during the drought.- Consequences? Birds with deeper beaks (which were more likely to survive drought) would theoretically become dominant in the population and get passed down from parent to offspring because of the higher fitness during the drought, which killed off the smaller beak depth finches. This is an example of directional natural selection.Outcome: The composition of the population changes from one generation to the next, generally for the better of the population.Pattern of beak shape evolution on Daphne Minor – “Darwin’s finches”Darwin noticed many things about these finches on the island; they varied in beak shape and ecologically. Beak shape implies the different ways of life.

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