Darwin's Comet Orchid

One of the many things Darwin understood well about the theory of evolution is that it does not occur in a vacuum (at least not the proverbial kind): the successful evolution of any organism can only be comprehensively understood in terms of the background and selection pressures to which said organism's lineage would have to adapt. This can create an arms race between competing creatures (think the ever-increasing speed of cheetahs and gazelles), or harmonious relationships between cooperative species.

This subtle insight implies that evolutionary theory can make predictions which can then be tested scientifically. In a remarkable and famous case, after after having inspected a peculiar species of orchid from Madagascar, Darwin predicted that there must exist a moth in that area with a peculiar feature: it would have a tongue many times its own body length...

And if you think that's impressive, check out what Alfred Russell Wallace predicted...

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