Howler Monkeys with Deeper Calls Have Smaller Balls

The smaller the size of the testes in a howler monkey species, the larger the size of the animal's hyoid bone, a structure that enables the monkeys to make deep, booming calls — noises on a par with those of a tiger, though howler monkeys are only about the size of cocker spaniels. The relative sizes of the hyoid bones and testes appear to be related to how the animal lives and reproduces, according to a new study, published today (Oct. 22) in the journal Current Biology. Curiosity about t