HUMAN INTELLIGENCE 277As Vygotsky put it, “By being included in the pro cess of be hav ior, the
psychological tool alters the entire fl ow and structure of mental func-
tions. It does this by determining the structure of a new instrumental act
just as a technical tool alters the pro cess of natu ral adaptation by deter-
mining the form of labor operation.”^22
Vygotsky concluded that human thought and activity is embedded in
social life from the moment of birth. He argued that the entire course of
a child’s psychological development from infancy is achieved through
social means, through the assimilation of cultural tools. Th e highly com-
plex forms of human cognition, he argued, can only be understood in the
social and historical forms of human existence. From toilet training to
becoming an airline pi lot, a scientist, or a bus driver, socially devised
tools become individual cognitive tools. Th is is the basis of his “law of
cultural development”: “Any function in the child ’s cultural development
appears on stage twice, on two planes. First it appears on the social plane,
then on the psychological, fi rst among people as an inter- psychical cate-
gory and then within the child as an intra- psychical category.”^23
It now seems certain that it is precisely for the assimilation of such
tools that the extreme plasticity of the human brain evolved: a brain for
the internalization of socially devised apps rather than one reliant on
built-in routines. Th e big diff erence is that, unlike the apps we download
for phones and computers, the brain constantly refashions them and feeds
them back into the collective. Nevertheless, we now know from brain
imaging and other studies how background experience with specifi c
cultural tools or procedures results in corresponding changes in brain
networks.^24
For example, such experience oft en refl ects occupational specializa-
tion. London taxi drivers, who are required to develop a detailed mem-
ory of street layouts, show enlargement of that part of the brain involved
in spatial memory (the posterior hippocampus). Likewise, the part of the
cortex involved in the sensorimotor aspects of fi n ger coordination in vi-
olin players is expanded on the corresponding side of the brain, but not
on the other side. Another study showed changes in cortical thickness
and hippocampal volume following intensive foreign language learning
in army trainees. In an article titled “Culture Wires the Brain,” Denise
C. Park and Chih- Mao Huang review studies suggesting that even subtle
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