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1999). Note that complex social behavior is also shown by other social non-
primate mammalian species. Thus, there are two interesting aspects to human
sociality: it served as an evolutionary constraint which led to an increase of
brain size in primates, which in turn led to an increased capacity to further
develop social complexity.
Dunbar and his collaborators found evidence (cf. Dunbar (1992); Dunbar
(1993); Barton & Dunbar (1997); Dunbar (1998)) that the size of a cohesive so-
cial group in primates is a function of relative neocortical volume (volume of
neocortex divided by rest of the brain). Such a correlation has not been found
for ecological variables (hypothesizing e.g. that dietary considerations or the
size of home ranges caused an increase in brain size). It is therefore suggested
that social complexity played a causal role in primate brain evolution, namely
that in order to manage larger groups, bigger brains are needed to provide the
required 'information processing capacity'. The neocortex, which accounts for
50-80 % of total brain volume in primates, is generally associated with cog-
nitive processes such as reasoning, mental manipulations and consciousness.
Compared with more primitive parts of the brain, the neocortex size substan-
tially increases from insectivores to prosimians, anthropoids, and humans. In-
deed, it has been shown that primate species with relatively larger neocortices
exhibit more complex social strategies than species with smaller neocortices
(Pawlowski et al. 1998). It is also suggested that the relationship between en-
cephalization (relationship between brain size and body size) and social com-
plexity is not unique to primates. For example, findings reported in (Marino
1996) suggest that
cetaceans
(whales, dolphins, and porpoises) and primates
show similar relationships between relative brain size and group size (a mea-
sure of social complexity). Similarly, Dunbar and Bever (1998) show that neo-
cortex size predicts group size in carnivores and some insectivores. Also, bats
that have stable social groups have a larger neocortex than bats that do not live
in stable social groups (Barton & Dunbar 1997).
According to the SIH, primates are good primatologists, namely they are
experts on social matters in a
laser-beam
form of intelligence. According to the
SIH, during the evolution of human intelligence a transfer took place from
social to non-social intelligence
2
so that hominid primates could transfer their
expertise from the social to the non-social domain. An interesting aspect of this
kind of transfer is discussed in (Mithen 1996). He explains the evolution of an-
thropomorphic thinking with an accessibility between the domains of social
intelligence and natural history intelligence so that “people could be thought
of as animals, and animals could be thought of as people” (Mithen 1996: 224).
Furthermore, the accessibility between the domains of social and technical in-
