Atavism is the reappearance of a characteristic in an organism after several generations of absence, usually caused by the chance recombination of genes.
In humans, these evolutionary throwbacks may include vestigial tails, large canine teeth, extensive hair growth on body, supernumerary nipples and face and extra - or webbed - fingers and toes.
The best-known vestigial organ in humans is the appendix. The original function of the appendix, which can still be observed in many herbivorous mammals, is "as a fermenting vessel ... containing bacteria that help the animal break down cellulose into usable sugars."
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhhihSQRC1Jvaic4ovJnDOljDmNklMP6nOobKngUFqo-fRWfHiGoRKqzdFmVO6HpnJ6UxHBSJDctvgcZZVE99FxpQG7v5GvsIHEa7gnGzNfpdj1wKxarShI_5HnRkSji-VXeurqb9WYb5Q/s320/pagee154atavism.gif)
Another vestige of our past is goosebumps, which we get when we're cold or feel threatened but are basically useless. But in mammals that actually have fur, raising that fur would be useful to insulate from the cold or to appear larger when threatened – exactly the same two situations.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgji90-ZzaMsrk_TydN51aiSaxs9iMfXZ-pyC7sWp3Di1E2O07DUeBqohs1-XK9fkboztHdNQcK1peXUP53D2Zw9Wi_f2irW7GK9TyrONq3A2ZnM9t43qZoytJY_EASOBz0NdHrcXqoDqQ/s320/Ear+Comparison.png)
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