Baby, I'm howlin' for you. Male howler monkeys make deep and boisterous calls to attract mates, but the deepest-pitched songs may come at cost: the size of their testicles. A new study in the journal ...

For howler monkeys, it appears the louder the calls, the smaller the — ahem — balls. A research team looking into the monkeys’ incredibly loud and low vocalizations, and the physical structures that ...