Anthropologists measured human skulls at various periods in history and found that the average brain capacity of contemporary adults is 1349 milliliters, compared with the brain capacity of Mesolithic humans, the brain capacity of men is reduced by 10%  The brain capacity of women is reduced by 17%
Contemporary brain science research shows that a smaller brain capacity makes humans more cooperative.
 The researchers believe that in an era of increasingly clear division of labor, people with a cooperative spirit have more opportunities to survive and reproduce than others, and survival of the friendliest is an important reason for the shrinking human brain