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Guppy spots are largely genetically controlled. Spots that help the guppy blend in with its surroundings protect it from predation, but spots that make it stand out help it attract mates. In this experiment, guppies were raised in ponds that varied in the coarseness of gravel on the bottom. All ponds had predators. After fewer than 15 generations of selection, the markings of guppies in different ponds had substantially diverged as a result of natural selection. In the presence of predators, guppies evolved to blend in with their background.

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