Frogs

Researchers have observed frogs spontaneously changing genders in the lab. Now they’re observing it in the wild too, and it’s not a natural process. More and more male frogs are becoming females, complete with fully functioning reproductive organs. The frog-feminizing culprit? A common weed killer called atrazine.

Banned in Europe, atrazine ends up running into rivers and lakes where it wreaks havoc on frog sexual development, suppressing production of testosterone (the male sex hormone) and boosting the female sex hormone estrogen. Not good news for amphibian populations that are already declining from climate change, loss of habitat and invasive species.