A Game of Selection: You Win or You Die!!! Evolution: What does it mean??? Evolution: How do we define it? Change in avg phenotype over time Evolution: How do we define it? Change in avg phenotype over time Change in allele frequency over time Mechanisms of evolution? Genetic drift Biased mutations Gene flow Natural selection Gradual nonrandom process by which biological traits become more/less common in a population due to differential reproduction Three components of natural selection Variation traits are variable within populations Selection traits affect fitness (ability to survive and reproduce) Heredity traits are heritable across generations Variation Selection Light > Dark Coloration Fitness (# offspring) Heredity Three components of natural selection Variation Selection Heredity When these components are all present you will have evolution by natural selection! Types of selection Directional Stabilizing Disruptive Directional Species of mouse that lives among dark rocks where dark fur conceals them from predatorswhat is going to happen to the population over time? Directional Species of mouse that lives among dark rocks where dark fur conceals them from predatorswhat is going to happen to the population over time? Stabilizing If the species of mouse lives in an area with rocks of intermediate color what do you think is going to happen to the population over time? Stabilizing If the species of mouse lives in an area with rocks of intermediate color what do you think is going to happen to the population over time? Disruptive Sticking with the mouse example, imagine the species lives in an area made up of patches of light colored rocks and patches of dark colored rocks.what do you think will happen to the population over time? Disruptive Sticking with the mouse example, imagine the species lives in an area made up of patches of light colored rocks and patches of dark colored rocks.what do you think will happen to the population over time? Important to keep in mind! Selection can only act on existing variation Here is a population of bacteria with individuals varying in their degree of antibiotic resistance. What will happen when antibiotic is added? No resistance > High resistance Important to keep in mind! Selection can only act on existing variation No resistance > High resistance Antibiotics added Antibiotic resistance was already present in the population, it does not arise in response to the antibiotic. Important to keep in mind! Selection can only act on existing variation No resistance > High resistance Antibiotics added Final population Important to keep in mind! Individuals are selected but populations evolve A population of cute furry rabbits have recently migrated into a new environment that is much colder than their home range. Having thicker fur provides a large advantage in this new environment. When the rabbits first arrive their population consists of individuals with a wide range of fur thickness. This is Bob. Bob is a rabbit with a pretty thin coat of fur. Will Bob be able to adapt to the new environment? Important to keep in mind! Individuals are selected but populations evolve No. Bob and others like him will die off while those with thick fur survive and reproduce so that over time the population average fur thickness increases. Individuals cannot evolve themselves, populations evolve. Now its time for a game!