Disclaimer - this study was based solely on animals. Any apparent links between monkeys and men are purely coincidental................... A study published in Current Biology has found that the size of a monkey's testicles is directly linked to how loud his cat-call is. The research, which analysed the size of Howler Monkeys' testicles, found that those who had smaller balls had larger hyoid bones - which enable the monkeys to make louder, deeper mating cat-calls. Apparently, this is evolutionary - and the hyoid bone is directly linked to the monkey's social setting. Monkeys that live in a community where one male is having sex with several females were found to have smaller balls but larger hyoid bones. According to Women's Health, scientists claim that monkeys who live in these harem-style situations may use their deeper cat-calls to attract more females and scare off other males. Study author Leslie Knapp, explained that it is difficult to make a comparison between monkeys and humans, as humans have much smaller hyoid bones. We'll still be producing the study next time we're cat-called.