262 HUMAN INTELLIGENCEuncertainty was certainly involved. Th e older picture (now becoming
more complicated) was quite neat. Th e climate dried, forests thinned, and
former forest dwellers were forced onto the forest margins and open savan-
nah. Without natu ral defensive equipment and deprived of traditional
food resources, those species became extremely vulnerable. Th ey had to
face unreliable food supplies, which resulted in wide ranges and new diets,
exposure to large predators, and so on.
Th ey responded by cooperating with one another to a degree far out-
stripping that of any of their primate ancestors. But doing so presented
new demands on a cognitive system. Th e micro- environment of true
cooperation is vastly more intricate, and more demanding on cognitive
systems, than the macro- environment of climate, geophysical changes, and
the social groupings of nonhuman primates.
Th is was the context for the appearance of hominids (Th e word “hom-
inid” usually refers to members of the family of humans, Hominidae,
which consists of all species on our side of the last common ancestor of
humans and living apes). Some new adaptations were physical, such as
the adoption of bipedalism, pres ent in our earliest ancestors of 7.5 million
years ago. But the cognitive demands are much more impor tant. As
mentioned in chapter 8, they are pres ent to some degree in most primates.
Only in this new branch, however, did they really make a diff erence. De-
fense, hunting, and foraging became vastly more eff ective as an or ga nized
group than as a mere collection of individuals. Also, reproductive rela-
tions, child rearing, divisions of labor, sharing of products, and so on,
became less fraught when cooperatively ordered.
As also mentioned previously, some of that lifestyle is foreshadowed
in cooperative hunters like wolves and African hunting dogs. It was also
foreshadowed by a suite of pre- adaptations already evolved in some form
in the apes. Bipedalism occurs sporadically in some monkeys and apes
to provide height to see over tall grasses and shrubs and to wade in rivers.
It was further selected and improved in the hominid ancestors. Freed
hands permitted rudimentary tool use, which, together with the longer
visual perspective of open spaces, would have improved visuo- motor abil-
ities. Th ese factors may well have added the fi rst increment in brain size.
Th at, too, would have been anatomically fostered by the new bipedalism
and the ability to balance a heavier skull on top of the now- vertical spine.
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