A feature that an organism inherited from its ancestor but that is now less elaborate and functional than in the ancestor. Usually, vestigial structures are formed when a lineage experiences a different set of selective pressures than its ancestors, and selection to maintain the elaboration and function of the feature ends or is greatly reduced.

A process in which a species’ range is divided even though the species has remained in place. This might happen through tectonic action, geologic activity (like the rise of a mountain range or shift in the course of a river), or other processes. Vicariance is usually contrasted with dispersal as a biogeographic mechanism.

Any member of the animal clade Vertebrata. All vertebrates have a backbone that surrounds and protects the nerve cord, a character that they all inherited from their common ancestor. Vertebrates are a subgroup of the chordates. Modern vertebrates include fish, sharks, mammals, and amphibians.

Differences in genes, traits, or behaviors among members of a population, which may result in differences in reproductive success. When variation is genetic in origin, it may be acted upon by natural selection.