linguistic:paraphrasing, structural:reformatting
Encephalization

The human species eventually developed a much larger brain than that of other primates—typically 1,330 cm (81 cu in) in modern humans, nearly three times the size of a chimpanzee or gorilla brain. After a period of stasis with Australopithecus anamensis and Ardipithecus, species which had smaller brains as a result of their bipedal locomotion, the pattern of encephalization started with Homo habilis, whose 600 cm (37 cu in) brain was slightly larger than that of chimpanzees. This evolution continued in Homo erectus with 800–1,100 cm (49–67 cu in), and reached a maximum in Neanderthals with 1,200–1,900 cm (73–116 cu in), larger even than modern Homo sapiens. This brain increase manifested during postnatal brain growth, far exceeding that of other apes (heterochrony). It also allowed for extended periods of social learning and language acquisition in juvenile humans, beginning as much as 2 million years ago. Encephalization may be due to a dependency on calorie-dense, difficult-to-acquire food.

Furthermore, the changes in the structure of human brains may be even more significant than the increase in size. Fossilized skulls shows the brain size in early humans fell within the range of modern humans 300,000 years ago, but only got its present-day brain shape between 100,000 and 35,000 years ago.

The temporal lobes, which contain centers for language processing, have increased disproportionately, as has the prefrontal cortex, which has been related to complex decision-making and moderating social behavior. Encephalization has been tied to increased starches and meat in the diet, however a 2022 meta study called into question the role of meat. Other factors are the development of cooking, and it has been proposed that intelligence increased as a response to an increased necessity for solving social problems as human society became more complex. Changes in skull morphology, such as smaller mandibles and mandible muscle attachments, allowed more room for the brain to grow.

The increase in volume of the neocortex also included a rapid increase in size of the cerebellum. Its function has traditionally been associated with balance and fine motor control, but more recently with speech and cognition. The great apes, including hominids, had a more pronounced cerebellum relative to the neocortex than other primates. It has been suggested that because of its function of sensory-motor control and learning complex muscular actions, the cerebellum may have underpinned human technological adaptations, including the preconditions of speech.

The immediate survival advantage of encephalization is difficult to discern, as the major brain changes from Homo erectus to Homo heidelbergensis were not accompanied by major changes in technology. It has been suggested that the changes were mainly social and behavioural, including increased empathic abilities, increases in size of social groups, and increased behavioral plasticity. Humans are unique in the ability to acquire information through social transmission and adapt that information. The emerging field of cultural evolution studies human sociocultural change from an evolutionary perspective.