For biologist and herpetologist Tyrone Hayes, scientific breakthroughs don't begin and end in the laboratory. They also come from the field. Which is why, more often than not, you'll find Hayes wet, muddy, and knee-deep in an African swamp at 2 a.m., the time when the frogs come out.

Hayes grew up in South Carolina, and, as a boy, one of his favorite pastimes was tracking down the region's abundant turtles, snakes, and toads. That abiding fascination led Hayes to earn an undergraduate degree in organismic and evolutionary biology from Harvard University. He later received a Ph.D. in integrative biology from the University of California, Berkeley, where he currently serves as a professor.

Hayes says an interest in frog hormones, specifically those of a tiny reed frog common in Ethiopia and Uganda, sparked his interest in his current fieldwork. "Surprisingly, frog hormones are very similar, and in some cases identical, to human hormones," he says. "So what affects a frog may also affect humans."

It was during a night in the boggy African bush that Hayes's flashlight revealed an unexpected discovery: Several members of the reed frog genus had changed color. Males, which are normally green, had taken on the reddish background and white spots of females.

Seeking to understand why, Hayes arrived at a theory: During the metamorphosis from tadpole to adult, frogs are very sensitive to changes in their environment, including chemicals in the water or in their food supply. So the change in coloration indicated that the frogs' extremely thin, sensitive skin was reacting to contaminants in the water. Thousands of frogs later, Hayes and his research team have proved the theory correct.

Reed frogs, indeed, serve as tiny red flags that can warn when dangerous, even cancer-causing chemicals are present in a water source. These harmful substances may contain or act like hormones, triggering the color transformation. Contaminants include plastic by-products, pesticides in crop sprays such as DDT, and synthetic hormones such as DDS. Because they cannot be broken down during sewage treatment, the toxins flow into marshes and lakes.

"This is the same water people cook and bathe with," Hayes notes. "We've found developmental changes in tadpoles when water contains contaminants 50 times lower than what's allowed in U.S. drinking water. If chemicals in such low concentrations can impact amphibians, mammals may also be affected."

Hayes realized his simple observation could have enormous practical applications: Reed frogs could become a low-cost way to test for water pollution in developing countries. Local residents would only need to raise the frogs in questionable water sources and observe their color as adults to check for contaminants.

Hayes's findings reveal a crucial new link between conservation and health.