Mutualism  

Extract

A persistent problem

Mutualisms—mutually beneficial interactions between species—have a long history of being a problem. On the one hand, we see them everywhere, as bees visit flowers, birds eat fruits, legumes form root-nodules and as Herodotus and Aristotle described, tick-birds supposedly pick parasites from the teeth of crocodiles. But on the other hand, scientists have come up with a series of reasons why they should be rare, if they exist at all. Reality and biological theory have repeatedly come into conflict.

Darwin himself was perhaps the first to face this problem as he elucidated the implications of natural selection. He wrote in the Origin that “If it could be proved that any part of the structure of any one species had been formed for the exclusive good of another species, it would annihilate my theory, for such could not have been produced through natural selection” ( Darwin 1859 ). Realizing the seriousness of this challenge, he devoted his next book to the pollination of orchids by insects, showing in detail how both benefited ( Darwin 1862 ).