Sperm Count

There are large differences between sperm counts (total number of sperm found in an ejaculate) of humans and chimpanzees. Chimpanzees and bonobos ejaculate several times the number of sperm compared to humans (a billion plus sperm per ejaculation). There is also evidence that chimpanzees are capable of maintaining elevated sperm counts in successive ejaculations. These relatively high sperm numbers are achieved by large testis size (both total and relative to body size) found in chimpanzees and bonobos and are reflective of the high levels of sperm competition typical for these to species. Limited data on orangutan and gorilla sperm counts indicate lower numbers than humans, ~ 120 million for orangutans and 20 – 80 million for gorillas. There is much speculation with regard to sperm competition in humans. The human sperm count as well as human relative testis size put our species in an intermediate position between low sperm competition (as in gorillas) and high sperm competition (as in bonobos and chimpanzees).