POTENTIAL BETWEEN BRAINS 253of group size. It has simply been assumed that bigger groups will demand
more complex cognition for managing more relationships. Such social-
ity, even if accurately described, is a far cry from the kind of complexity
required in, say, group hunting among wolves.
Anyway, correlations have been reported between size of cortex and
group size across diff er ent primate species. Th e trou ble is that many other
attributes correlate with group size, such as body size and general (non-
social) learning ability. Christine Charvet and Barbara Finlay suggest
that, when account is taken of these, the correlation is unlikely to be signifi -
cant.^22 We still cannot be sure whether group living in primates is such
as to require greater cognitive abilities than everyday, “ecological,” prob lem
solving.
So what about cognitive ability in primate groups? Th is, too, has been
mea sured indirectly, in terms of the incidence of identifi able practical
skills. Simon Reader and colleagues assessed the degree of social learn-
ing, tool use, extractive foraging, and tactical deception in sixty- two pri-
mate species as reported in published papers. Th e statistically converted
data suggested low to moderate correlations with brain volume.^23
Interpretation is not straightforward, however. First, compiling data
from published sources requires copious adjustments and many assump-
tions. More importantly, the actual defi nition of these behavioral fl exi-
bilities as indices of cognitive ability is by no means clear. Social learning
is simply defi ned as learning through observation of, or interaction with,
others. Such learning has been reported in fi sh and birds, as mentioned
above. And as already implied, there is a big diff erence between observa-
tion and interaction, depending on how the latter is defi ned. Unfortu-
nately, in this area little micro- analy sis has been done of cause and eff ect
in the way that the microbiologist has revealed the intelligence of the cell,
or the embryologist the intelligence of development.
Fi nally, considerable variation exists in social cohesion across diff er ent
primate groups. Th e chimpanzee is considered the closest to humans
in terms of cognitive ability and brain size. But as Craig Stanford put it,
“Chimpanzee society is called fi ssion- fusion, to indicate that there is little
cohesive group structure apart from mothers and their infants; instead,
temporary subgroupings called parties come together and separate
throughout the day.”^24
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