Can’t believe you’re making me Google this stuff!
Male chimpanzees are much larger than females, and they have a multi-male to multi-female mating system. Essentially, male chimps have sex all the time with any female and with any excuse. A female therefore may contain sperm from multiple partners at any one time, which puts the sperm itself – and not just the animals that produce it – into direct competition. For this reason, chimpanzees have evolved huge testicles in order to produce massive amounts of sperm, multiple times a day.
Male gorilla are also much larger than females, but they have a polygynous or harem-style mating system where many females live with a single male. With little or no competition actually inside the uterus, gorillas have had no need for a testicular arms race to facilitate the production of more and more sperm. Their testes, therefore, are relatively small. This is similar to modern humans, whose testes are also of very modest size and produce a relatively small amount of sperm. In fact human sperm count reduces by more than 80% if men ejaculate more than about two times a day.
Sounds like someone was desperate for some points in a pub quiz and she done you over with the old “I studied this at degree level” line.