Another feature unique to humans that evolved following early weaning and high fertility was “encephalization.” About two million years ago, when the human brain size began to increase, our ancestors prioritized the growth of brain in childhood, and delayed the growth of the body.*

From that time on, human babies were born with a high proportion of body fat, and spent much of the energy from that fat on brain growth.

■References (Books, papers, Web articles, etc.)
家族進化論』 第4章・第10節 脳の大きさと生活史の変化  山極寿一 (東京大学出版会、2012)

*Humans have a much larger brain than other animals. In the process of human evolution, the genus Australopithecus maintained a small brain, similar to gorillas (about 500 cc), while the brain of Homo erectus grew larger (to about 950 cc), and that of Homo sapiens reached our present brain-size (about 1350 cc).

The phenomenon of the cerebrum in the central nervous system growing relatively large is called “encephalization.” [Editorial note]

Related iCards: Meat eating in primates (Vol 1.) / Use of fire and brain growth (Vol 1.)

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