And it supposedly works. A study about howler monkeys has found that monkeys who scream the loudest also tend to have smaller testes and a shortage of sperm compared to their peers.
Howler monkeys are one of the few nest-building monkeys, and one of the loudest animals. They live in groups of 6-12 individuals, wich consist of a few males and many more females. Biological anthropologist Jacob Dunn and his team from Cambridge University wanted to see how the size of the monkey testicles influences social arrangements, and how they correlate with their screams. Someone should do this study with humans as well.
The team calculated how loud monkeys scream depending on the size of their testicles.
“The results of our acoustic analyses show that howler monkeys produce roars at a similar frequency as tigers, which is far lower than we would have predicted from their body size, yet exactly what would be predicted from measuring their giant vocal folds’ which are three times bigger than in a human. It may be that investment in developing a large vocal organ and roaring is so costly that there is simply not enough energy left to invest in testes. Alternatively, using a large vocal organ for roaring may be so effective at deterring rival males that there is no need to invest in large testes.”
Surprisingly, it actually works. Males with small testes and loud screams are more likely to gather a large female following.
Dr. Dunn’s team should definitely try to replicate this study with human subjects. I know many examples of men who are living proof that these findings also apply to humans.