Why Do Male Chimps Have Big Balls?
Large testicles, relative to body weight, usually indicate fierce sperm competition among the males of a species. Male chimps are known for their rather large balls. This is not, however, because the male chimps inseminate lots of females. If a female chimp were to become pregnant easily, there wouldn't be much need for the male to produce lots of sperm. The reason why male chimps have such large balls is because females chimps are very promiscuous. Female chimps will look to copulate between five hundred and a thousand times for each pregnancy, with many different males, either inside or outside their extended family group.