As a graduate student in the late 1970s, David Reznick set out on a modest quest to test a key part of the theory of evolution. Reznick wanted to examine Charles Darwin's concept of the struggle for existence - specifically, how predator-prey interactions shape the evolution of new species. Enthusiastic and ambitious, he intended to do it in the wild. "I wanted to watch evolution happen," says Reznick, now an evolutionary biologist at the University of California, Riverside. So in 1978, he flew to Trinidad in search of guppies. Armed with a topographic map traced onto a piece of notebook paper, he headed into the Caribbean island's rugged Northern Range. Working under a canopy of tropical trees amid squawking birds, multicolored butterflies and boas, he collected 1,600 guppies, a colorful fish species so prolific that the females can produce dozens of babies every three to four weeks. Reznick was curious to see if predators could affect genetic adaptation in guppies over a short time.
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