Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

Complex biological structures that have been built up by natural selection (that has used random mutations as the raw material) and therefore currently fill some vital function. They can be divided into two categories, adaptations and exaptations. Adaptation encompasses structures that fulfill the same function from the very beginning and were formed and developed as a consequence of the action of the same selection pressure as is acting on them at the present time. See also exaptations.