The Frog of War

Darnell lives deep in the basement of a life sciences building at the University of California-Berkeley, in a plastic tub on a row of stainless steel shelves. He is an African clawed frog, Xenopus laevis, sometimes called the lab rat of amphibians. Like most of his species, he's hardy and long-lived, an adept swimmer, a poor crawler, and a voracious eater. He's a good breeder, too, having produced both children and grandchildren. There is, however, one unusual thing about Darnell.

He's female.

Genetically, Darnell is male. But after being raised in water contaminated with the herbicide atrazine at a level of 2.5 parts per billion—slightly less than what's allowed in our drinking water—he developed a female body, inside and out. He is also the mother of his children, having successfully mated with other males and spawned clutches of eggs. Recently he was moved to an atrazine-free tank and has turned lanky, losing the plump, pincushion look of a female frog. But last March, when UC-Berkeley integrative biology professor Tyrone B. Hayes opened him up to take a look, Darnell's insides were still female. "He still has ovaries, but there's no eggs in them," Hayes told me the next day as we stood watching the frog, who swam over and inspected us soberly, then turned and flopped away.