Darwin's Predictions

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An insect with a foot-long tongue must exist to pollinate this orchid.

Not all of Darwin's conjectures were so broad in scope or so earth-shaking; some were simple predictions. Take the case of this species of orchid, Angraecum sesquipedale, from Madagascar. When Darwin saw this orchid in 1862, he, like anyone who saw it, was astonished by the length of its spur, which can reach over a foot in length. (See long, slim tube in photo.) "Astounding," he wrote. "What insect could suck it?" For some as-yet unknown insect must, he insisted, and it had to have a foot-long tongue to get at the plant's nectar, which pools at the very base of the spur. Entomologists of his day were skeptical, for no such creature had ever turned up. But several decades after Darwin's death in 1882, scientists discovered a giant hawk moth in Madagascar, and it lapped the orchid's nectar with, yes, a foot-long tongue. The moth was named Xanthopan morganii praedicta in honor of his prediction. Once again, Darwin was right.

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