Meat eating was behind the evolutionary success of humankind, because this higher-quality diet meant that women could wean their children earlier:
Among natural fertility societies, the average duration of breast-feeding is 2 years and 4 months. This is not much in relation to the maximum lifespan of our species, around 120 years. It is even less if compared to our closest relatives: female chimpanzees suckle their young for 4–5 years, whereas the maximum lifespan for chimpanzees is only 60 years.
Many researchers have tried to explain the relatively shorter breast-feeding period of humans based on social and behavioral theories of parenting and family size. But the Lund group has now shown that humans are in fact no different than other mammals with respect to the timing of weaning. If you enter brain development and diet composition into the equation, the time when our young stop suckling fits precisely with the pattern in other mammals.
This is the type of mathematical model that Elia Psouni and her colleagues have built. They entered data on close to 70 mammalian species of various types into the model — data on brain size and diet. Species for which at least 20 per cent of the energy content of their diet comes from meat were categorised as carnivores. The model shows that the young of all species cease to suckle when their brains have reached a particular stage of development on the path from conception to full brain-size. Carnivores, due to their high quality diet, can wean earlier than herbivores and omnivores.
The model also shows that humans do not differ from other carnivores with respect to timing of weaning. All carnivorous species, from small animals such as ferrets and raccoons to large ones like panthers, killer whales and humans, have a relatively short breast-feeding period. The difference between us and the great apes, which has puzzled previous researchers, seems to depend merely on the fact that as a species we are carnivores, whereas gorillas, orangutans and chimpanzees are herbivores or omnivores.