The reciprocal evolutionary change in two or more species that interact closely with each other, where each species acts as a selective pressure on the other. Changes in one species drive evolutionary responses in the other.
From Latin prefix 'co-' meaning 'together' and 'evolutio' meaning 'unrolling or development'. The term was coined in 1964 by entomologists Paul Ehrlich and Peter Raven to describe the evolutionary arms race between plants and their herbivorous insects.
Coevolution is like an eternal evolutionary arms race - as flowers evolved longer tubes to avoid being robbed by short-tongued insects, some insects evolved longer tongues to reach the nectar! There's actually an orchid in Madagascar with a foot-long nectar tube that Darwin predicted would have a matching moth - and they found it 40 years later.
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