Territorial conflict may explain male primates’ large size

Territorial conflict may explain male primates’ large size Skip to content Subscribe today Every print subscription comes with full digital access Subscribe Now By Jake Buehler May 12, 2026 at 7:01 pm Share this: Share Share via email (Opens in new window) Email Share on Facebook (Opens in new window) Facebook Share on Reddit (Opens in new window) Reddit Share on X (Opens in new window) X Print (Opens in new window) Print It’s a game of monkey mean, monkey grew. Territorial tension may be behind the size of male primates. In many primate species, males have evolved to be bigger than their female counterparts, a disparity typically attributed to competition among socially related males for access to females. But bigger bodies may be more about dissuading conflict with males from rival groups , researchers report May 13 in Biology Letters .  “The traditional explanation is incomplete,” says Cyril Grueter, an evolutionary anthropologist at the University of Oxford.  Many species in the primate order — which includes monkeys, apes and lemurs — have sexual size dimorphism, meaning an average size difference between the sexes . While some primates like gibbons show barely any size disparity, others such as baboons and gorillas can have males that are twice as massive as the females. Most research on this pattern has centered on male-male competition for females within a social group, Grueter says. Bigger, stronger males can outfight or intimidate smaller males, giving them better access to mates.  “But primate groups are rarely isolated,” Grueter says. Neighboring groups commonly interact. They overlap in territory and compete for resources such as food and mates. During his Ph.D. research, Grueter found that African leaf-eating monkeys with more contact between groups had especially large males compared with females. He and his colleagues wanted to see if that relationship extended to other primates. The researchers gathered data on 146 primate specie