Evolution

Definition of Evolution Change over time or specifically: * Change in average phenotype over time *Change in allele frequency over time

Mutations and Evolution Mutations – essential for evolution Can cause changes in behavior, phenotypic ratios (overall appearance of the organism), or physiology

Mechanisms of evolution? Genetic drift Biased mutations Gene flow Natural selection

Natural selection Gradual nonrandom process by which biological traits become more/less common in a population Industrial Revolution

Requirement for Natural Selection Variation – traits (many colors, heights, strengths, etc.) are variable within populations Selection – traits affect fitness (ability to survive and reproduce) Heredity – traits that can be passed down to other generations.

Variation

Light ---------------------> Dark Selection Fitness - Fitness (# offspring) Light ---------------------> Dark Coloration

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 predators…what is going to happen to the population over time?

Directional Species of mouse that lives among dark rocks where dark fur conceals them from predators…wh at 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 Antibiotic resistance was already present in the population, it does not arise in response to the antibiotic. Antibiotics added No resistance -------------------> High resistance

Important to keep in mind! Selection can only act on existing variation Antibiotics added Final population No resistance -------------------> High resistance

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!