Patterns and Mechanisms of Evolution

Coevolution

The change in two or more species in close association with each other.

Divergent Evolution

Species that once were similar to an ancestral species become increasingly distinct.

Adaptive radiation

Several populations of a single species diverge simultaneously into a variety of species.

Convergent Evolution

Two or more dissimilar and distantly related lineages can evolve in ways that make the organisms resemble each other superficially.

Analogous structures

Structures that have the same function and often the same basic external appearance but different origins.

Rate of Evolution

How fast do old species converge, diverge, or radiate?

Gradual Evolution

Each species undergoes gradual changes in its genetic makeup and phenotype.

Punctuated Equilibrium

Speciation occurs rapidly with long periods of stability.

Stabilizing selection

Individuals with average term of trait have highest fitness.

Directional selection

Favors phenotypes at one extreme of the phenotypic range.

Disruptive selection

Individuals with either extreme variation of a trait have greater fitness than individuals with average form.

Evolution

Evolution is a change in a species over time.

Heritable variations

Variations that exist within a population and can result in differential reproductive success.

Lamarck's theory

Inheritance of acquired characteristics based on physical needs of an animal.

Descent with modification

All organisms descended with changes from a common ancestor.

Natural selection

Increases survival and reproduction of individuals better adapted to the environment.

Fossil record

Paleontologists find fossils of intermediate forms.

Comparative Anatomy

Anatomy of living species should resemble extinct relatives if evolution occurred by natural selection.

Homologous structures

Anatomical signs of descent with modification.

Vestigial organs

Structures with no apparent sense but resemble useful structures in probable ancestors.

Comparative Embryology

Study of the similarities and differences in the embryos of different species.

Molecular Clocks

If life evolved from common ancestors, all living organisms should share basic features at the molecular level.

Adaptation

Any heritable traits that sustain organisms to its natural function in the environment.

Fitness

Measure of how well suited an organism is to survive in its habitat and maximize the numbers of offspring surviving to reproductive age.