Blackwell Publishing

Adaptive explanation - Is perfect adaptation possible?


Time lags

Adaptations will often be imperfect because evolution takes time, and natural selection cannot operate as fast as the environment of a species change. The environments of all species change more-or-less continually because of the evolutionary fortunes of the species they compete, and cooperate, with. Each species has to evolve to keep up with these events, but at any time they will lag behind the optimal adaptation to their environment.

The degree of lag can be quantified as lag load.

Examples of adaptations which are imperfect as a result of time lags include many fauna, the fruits of which will be out of date, and adapted to an earlier form of dispersal agent. Janzen and Martin have argued that the fruits of many of the forests of South America are 'neotropical anachronisms': they are anachronistically adapted to the fauna of large herbivores which are now extinct.

Image: the fruits of Annon purpurea (top) and Crescentia alata (bottom) were probably eaten by large herbivores that recently went extinct.

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