Evolution What is evolution Biological evolution is NOT

Evolution

What is evolution? • Biological evolution is NOT just a change over time. • The definition of evolution is Descent with Modification Some sort of change within a lineage.

What is a species? • Biological species concept: This concept states that "a species is a group of actually or potentially interbreeding individuals who are reproductively isolated from other such groups. "

Mechanisms of Evolution • How does evolution work? • What are the selective forces that cause evolution to occur? • How can we get genetically DIFFERENT organisms that come from the SAME common ancestor?

Descent with Modification • Recall, there needs to be some long term change of the gene frequency over time. More beetles have genes A Drought causes a decrease in food. B for green color and years later more brown beetles than green ones.

Modes of evolution 1. 2. 3. 4. Genetic Variability Mutation Genetic Drift Natural Selection

Genetic Variation Gene Flow Movement of genes from one population to another. Mutation Sexual reproduction causes new combinations of genes. Changes in DNA

Mutations Causes: Mutations are RANDOM 2 Types: Somatic-not in gametes so they are not heritable. Germ-found in gametes so they are heritable. 1. DNA copying error 2. Environment

Effects of Mutation • Negative effects – Persist in very low frequencies – Could be a lethal mutation or cause sterility • Positive effects – Beneficial mutations spread rapidly – Individuals with a beneficial mutation have a selective advantage

Genetic Drift • Frequencies of particular alleles may change by random chance • Prevalent in small populations

Bottleneck Effect • Drastic reduction in population • High risk of mutation • Little Variability

Founder Effect • Founder effect – few individuals in a new population • High risk of mutation • Little Variability

Natural Selection • Natural selection is the process by which individual organisms with favorable traits are more likely to survive and reproduce.

From Theory to Reality • There is no magic threshold when a new species is “made” • Evidence Supports Theory of Evolution – Vestigial Elements • Elements that have appeared to have lost any usability • Eyes in cave organisms • No light = no eyes, but organisms still have eye sockets

Making new species • New species are made when. . . – Isolation of two populations – Reduced gene flow between them – Selection/Genetic drift – Altered genetic composition

Once Isolation Occurs • Selection – different pressures driving different phenotypes/genotypes • Genetic Drift – change in genetic makeup of a population to do random changes • ***Isolation of “populations” allows these random changes to accumulate***