Mechanisms of Evolution and Natural Selection UMD

Evolution

The change in allele frequency over time

Genetic drift

Nonadaptive. Random changes in allele frequency due to chance events (ex: natural disasters)

Natural selection

An adaptive type of evolution. Theory of how evolution occurs that is widely accepted.

4 Principle of Natural Selection

• Heritable Variation: There is a heritable variation (has many differences in traits that can be inherited)

• Struggle/Competition: Individuals experience struggle and compete for resources

• Differential Reproductive Success: Organisms with more beneficial traits are more likely to survive and pass on traits which lead these traits to pass on to more generations

• Change in allele frequency over time (more or less)

Gene flow

Nonadaptive. Caused by a movement of individuals (emigration/immigration) between populations which transfers genes from one population to another.

Mutation

Nonadaptive. Creates new alleles

Bottleneck effects

Events that kill a large population

Founder effect

When a new colony is founded by a few members of the population

Directional selection

Selection shifts the population mean, increasing or decreasing a trait

Stabilizing selection

Selection against both extremes, which kind of meets the traits at the middle

Disruptive selection

Selection against intermediate phenotypes, meaning extremes are preferred

Can individuals evolve?

No because evolution happens across generations

Homologous structures

Those that have similar underlying features and come from a common ancestor, but different uses. Caused by divergent evolution.

Convergent evolution

Features that might look similar or achieve the same goal, but didn’t come from a common ancestor

Fossils

Earth is old and extinction is common. By using radiometric dating through looking at the radiometric isotopes in the rocks, people can find the age of these fossil which can help with learning about the transitions that led to current life.

Vestigial Structures

Structures that have limited use, but shine a light on relatedness

Biogeography

Study of distribution of organisms which shows how showing that species are distributed across Earth in patterns that reflect their evolutionary history and geological changes

Genetics/DNA Similarities

Hierarchy is consistent with other phylogenies (the evolutionary history and development of a group of organisms)

Divergent evolution

organisms diverge from a common starting point

Artificial selection

Humans manipulating organisms so that they pass certain traits which shows how organisms aren’t fixed and natural selection changes them