SO WE’VE GOT THAT GOING FOR US, ANYWAY: Human Penises Are Gigantic Compared With Other Primates. “Flaccid, the penis of the gorilla and the orangutan, both with much bigger bodies, is virtually invisible; erect, it reaches 1.5 inches or less; the chimpanzee, man’s closest relative (sharing 98 percent of his DNA) achieves an erection twice that of the other two apes but still only one-half the average human one. Why, comparatively, man’s penis is so disproportionately large is a question that engages a clutch of disciplines including archaeology, anthropology, and zoology, as well as the evolutionary, psychological, and sociological branches of biology. Collectively they remain at a loss.” Like big antlers, it’s to attract chicks.