Bio 117 The Imperfection of Life

Define: adaptation

a phenotype that is selected for within a population; heritable (measurable) trait that increases the fitness of the individual with that trait

Define: contrivance

adaptation within an organism, where the adaptation exists as a result of the modification of the previous adaptation of the ancestor

Define: vestigial trait

a trait the entire species has that is no longer used/has no use in the present environment, but was likely an adaptation for the ancestor

Define: atavism

a vestigial trait that only a few in the species have

Define: exaptation

pre-adaptation; a trait that was adaptive under a prior set of conditions and alter provides the initial stage for evolution of a new adaptation (contrivance) under a new set of conditions

Are all adaptations contrivances?

No

Are all contrivances adaptations?

Yes

What is the relationship between exaptations and contrivances?

Ancestor had an exaptation (adaptation); current adaptation is a contrivance.

Why are adaptations imperfect?

(1) They are compromises, produced by competing selection pressures. Some adaptations may exist in direct conflict with each other. (2) The environment changes over time, but adaptations lag seeing as they are made for the parent generation's environment. (3) Adaptations are limited by historical constraints; natural selection works primarily with alleles that have been present for many generations. Adaptive changes in morphology usually small modifications made of existing structures.