Final answer:
Human testicles are larger than gorillas' due to less extreme sexual dimorphism and a need for sperm competition, but smaller than chimpanzees' because of our species' mix of monogamous and polygynous mating strategies.
Step-by-step explanation:
The comparison of testicle sizes in human males to those of gorillas and chimpanzees can be explained by the different reproductive strategies and sexual dimorphism observed across these species. Gorillas exhibit a high degree of sexual dimorphism, with males typically being about twice the size of females, which correlates with a social structure where a single male mates with multiple females and competes less for mates, leading to smaller testicles. On the other hand, chimpanzees have relatively less sexual dimorphism with more intense competition among males for mating, resulting in larger testicles for sperm competition. Humans fall between these two extremes, with a moderate level of sexual dimorphism and testicle size that reflects our evolutionary history of both monogamous and polygynous mating systems.