Do males with bigger testicles have deeper voices? The jury is still out on humans, but if you’re a howler monkey, forget about it. A new study finds that the animals can make a lot of noise or a lot of sperm—but trying to do both just takes too much energy. The findings shed important new light on the kind of evolutionary tradeoffs animals must engage in to ensure the survival of their species.
The study is “long overdue,” says Dawn Kitchen, a physical anthropologist at Ohio State University, Columbus, who was not involved with the work. The results, she says, are “robust and clearly point to a trade-off.”