No, seriously. In human “natural fertility societies,” meaning groups that don’t use birth control, women breastfeed their children for an average of 27 months — until toddlers reach 2 years and a few months in age. Chimps, gorillas, and orangutans breastfeed for four to six years before weaning their young. Since these great apes live only five to six decades at the very most, they spend a much greater portion of their years nursing than their human relatives.
Why this large difference exists has been a scientific mystery for years. But recent research, comparing the weaning patterns of 67 mammalian species, points to a new answer: meat-eating. The researchers found that carnivores — animals that get 20 percent or more of their energy from meat — stop nursing their young earlier than non-carnivores. This group includes humans, tigers, and killer whales. What their research hasn’t told us is why meat-eating that allows earlier weaning.