HUMAN INTELLIGENCE 267Aft er years of making comparisons, Michael Tomasello says that
humans are evolved for collaboration in a way that the apes are not. Th at
is, richer connections between cortical and aff ective centers in brains
have fostered deeper awareness of others through relations among brains.
Not only can humans think what others are thinking, but they can also
feel what others feel.
Tomasello’s studies show that, although chimps may collaborate spo-
radically, human children collaborate obligatorily. For example, in a joint
activity producing rewards, either chimp is likely to purloin all the re-
wards, whereas children share equally. Children prefer to work jointly
rather than individually, whereas chimps rarely show intention to collab-
orate. Children reject unfair rewards in joint activities and will not tolerate
free riders.^11
True cooperation permitted habitation of increasingly marginal terri-
tories, and co- evolutionary eff ects made the biology of humans unique
in other ways. Dangerous living, widespread migration, and constant
testing of new habitats meant that our ancestors passed through some
periods of intense biological se lection. Such periods, which would have
been ones of rapid elimination of the less fi t—in this case fi t to partici-
pate cooperatively— are referred to as ecological bottlenecks. Th is would
have further ensured the good- enough fi tness of survivors.
As a result, genes have followed culture— selected to support socially
devised innovations— not vice versa. Our human ancestors migrated
from the African savannahs, across the Alps into Northern Eu rope, and
northeastward into Asia between 150,000 and 60,000 years ago. In doing
so, they would have encountered a colder climate, diff er ent food sources,
and new predators. Ge ne tic se lection supported some specifi c adapta-
tions, such as skin lightening, digestion of novel food sources, and
immunity to novel pathogens. But adaptability, as in food procurement,
the invention of warm clothing, use of fi re, robust dwellings, and so on,
took place at an entirely diff er ent level— a cultural one.
As a consequence, humans are remarkably alike genet ically. But by
being individually good enough to have brains to participate at that cul-
tural level, there is also a new eff ervescence of variation. Humans have
only a quarter of the ge ne tic variation of apes, our nearest biological
relatives.^12 In spite of that, human behavioral and cognitive diversity far
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