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In terms of genetic relatedness, humans are closest to chimpanzees, and to chimpanzees, the closest species are humans, not gorillas. The human-chimpanzee group shares strong male bond and collective hunting as their unique characteristics unseen in other anthropoids. However, on the other hand, humans have developed cognitive abilities that are distinct from chimpanzees and other anthropoids. In particular, abilities related to social cognition, such as imitation, empathy, instruction, mind reading of others and communication via language, are peculiar to humans and it is with these cognitive abilities that humans have created cultures and established civilizations. Why, then, did humans develop such special abilities in the first place?

Among hypotheses on the development of brain in primates, a dominant one, the Social Brain Hypothesis, explains that the recognition of social relationships and control of others in group life worked a strong selection pressure, and there have been reports on the strong correlation between the size of a group and the relative size of their neocortex. At the same time, recent research articles point toward a stronger correlation between breeding age and brain capacity (here, effects of body size are not considered). By means of cooking with fire and meat diet, humans were able to stabilize their group life by freeing themselves from dependency on fruits, which had been an anthropoidal tradition. In addition, with fathers and grandmothers taking active parts, they came to rear children by collectively sharing the burden in terms of time and labor. As a result, humans can produce children with late breeding age and large brain, with intervals between pregnancies that are far shorter than other anthropoids'. It seems that the above-mentioned ability of social cognition unique to humans grew as an adaptive tool for this cooperative procreation.

[Instructor]

HASEGAWA Toshikazu

Born in 1952. From Kanagawa Prefecture. Graduated from the Psychology Department, Faculty of Letters at the University of Tokyo in 1974. Finished doctorate course at the Graduate School of Humanities and Sociology (major in Psychology) of the same school in 1984. Ph,D. (Literature). After working as a specialist of dispatching international cooperation agents, Assistant at University of Tokyo's Faculty of Arts and Sciences, and Assistant Professor at the Faculty of Letters of Teikyo University,  Assistant Professor at the Faculty of Arts and Sciences of University of Tokyo since 1991 and since 1999 has served as Professor at its Graduate School of Arts and Sciences. Since 2011 the Dean of University of Tokyo's Faculty of Arts and Sciences as well as its Graduate School of Arts and Sciences. A member of the Science Counciol of Japan for its 21st term. Areas of Specialty: Ethology, Evolutionary Psychology.