How Populations Evolve

Questions about Fossils A fossil is an impression of a life form found in a rock. How did that impression get there?

Famous Fossils

Questions about Biogeography Biogeography is how organisms are distributed globally. What major discovery opened up the realms of Biogeography?

Questions from Comparative Morphology …why then produce vestigial structures (structures without a use)?

Comparative Anatomy Perhaps this is the perfect design? But…..

Comparative Embryology

Molecular Evidence

Missing Links Transitional fossils linking past and present

Modern Pieces of Evidence

Principles of Evolution Populations evolve, individuals don’t! Why must this be true? A population is a group of the same species, occupying the same area. A population exhibits variation among individuals. What is the cause of these variations?

Genetic drift Natural selection Gene flow Mutation Factors that alter gene frequencies

An evolving population Genetic drift is the random change in allele frequencies over generations. The magnitude of its effect relates to population size.

An evolving population The bottle neck effect: an extreme drift

An evolving population The founder effect: a few individuals from a large population leave and establish a new one elsewhere. Will the allele frequency of the founders be a good representation of the original population? Tristan da Cunha

An evolving population We know that all members of a population do NOT survive and reproduce. We also know that mating is NOT random …….the principles behind Natural Selection.

Different types of selection

Directional selection: the peppered moth

Different types of selection Stabilizing selection: favors the most common phenotype.

Different types of selection Diversifying selection: favors forms at the extremes and selects against the intermediate form.

Different types of selection Balancing selection: a variation on the stabilizing theme in which two or more forms of a trait are maintained in stable proportions.

Different types of selection Sexual selection: any trait that gives a competitive edge in mating and producing offspring (sexual dimorphism)