WEIT 2012 Chap3

Atavisms

What are atavisms?

Atavisms are remnants of what were former features of the species. They don't appear regularly but are occasinally present in individuals.

Why aren't atavisms recurrent in a species?

Atavisms are due to the sporadic reactivation of genes that are no longer needed by the species and have thus gradually disappeared because of natural selection.

How does natural selection make traits disappear?

Because of the environment in which a species evolves, some traits show more useful than others: useful to survive from predators, to find food, or more efficient regarding energy loss. Species with more useful traits tend to survive longer; therefore, they may reproduce more often, and transmit their traits to their offspring. Now, if sometimes traits "appear", others "disappear", and both can be useful, according to the situation.

How is it then possible that some traits appear again?

If the phenotype (the appearance) doesn't show a certain trait, it is still there in the genotype (the information); the genes related to the trait were deactivated: they "sleep" but don't disappear completely. Rarely, such genes "wake up", and an atavism is generated.