Researchers have identified a potential genetic link between gorillas’ small genitalia and infertility problems in male humans. Despite their impressive physiques, adult male gorillas have small penises and low sperm count. This is explained by their polygynous mating system, where dominant males monopolize females. Lacking sperm competition, gorillas’ sperm quality has not been subject to evolutionary pressure. The researchers examined gorilla genes that have undergone relaxed purifying selection, uncovering 578 genes that play a role in sperm production in fruit flies. By comparing these genes to data from infertile men, they found 109 genes that were more likely to have loss-of-function mutations in infertile men. These findings suggest a potential genetic basis for male infertility in humans, warranting further research to elucidate the specific roles of these genes.