“We found that males with larger hyoids, who can make lower-pitch vocalizations, have smaller testes and live in single-male groups with a harem of a few females,” anthropologist Leslie Knapp, a senior author of the study, said in a statement. “Males with smaller hyoids live in multimale groups and have larger testes.”

Sorry y’all. In this case the louder the monkey, the more females it gets.

Probably has smaller balls because the harem of females keeps them empty lol.