Bellow in the text, What does it suggest would be the difference between monogamous primates and primates living in a multi-female/multi-male group?

Group Size, Social Structure, and the Multiple Factor Hypothesis

If social interactions act as selection pressures, the strength of the pressure probably

depends in some way upon the salience of social interactions in an animal's life. An

animal that does not interact with others regularly faces a different environment from

one surrounded by conspecifics, so social pressures will shape the two differently.

Also, the nature of the interactions can be directly related to socio-ecological

variables.[13] Whether behavioral changes co-opt anatomical structures or whether

social pressures mold ontogeny involves currently untestable causal relationships.

Clutton-Brock and Harvey (1980) found that brain size correlated with home range

size in the cercopithecines[14] and that monogamous species have significantly

smaller brains than polygynous ones. These two socio-ecological factors are related,

for home range varies with troop size, and monogamous species have smaller troops

than polygynous ones. Dunbar (1992) claimed that after separating the various related

factors, only group size, of a host of behavioral ecology variables, remained

important. However, Sawaguchi's work demonstrates that not only do social structure

and diet correlate with neocortex size acrossprimates -- separating the primates into

three grades -- but also that within each grade selection pressures may be differentially

influential (Sawaguchi 1989, 1990, 1992; Sawaguchi and Kudo 1990).

Sawaguchi divided primates depending on their social structure (solitary and troopmaking for the prosimians and monogynous and polygynous for the anthropoids),

habitat (arboreal, terrestrial), and diet (foliovorous, frugivorous), into congeneric

groups in order to eliminate phylogenetic influence.[15] Using indices of `extra'

cortical parts (ECIs) (Sawaguchi 1989 after Jerison 1973 and Hofman

1982),[16] relative brain size (RBS) (Sawaguchi 1990 after Clutton-Brock and Harvey

1980), and relative size of the neocortex (RSN) (based on allometry between

neocortex volume and brain size) (Sawaguchi and Kudo 1990; Sawaguchi 1992;

Dunbar 1993),[17] Sawaguchi examined correlations between brain and neocortex

size and social structure and ecology and found that the different cerebral measures

gave different results. Only the ECI results and the 1992 RSN results will be

discussed here.

Due to inadequate comparative sample sizes, ECI correlations with social structure

could not be evaluated for old-world monkeys or for diet and habitat for new-world

monkeys. In new-world monkeys, polygynous groups had higher ECIs than

monogynous groups, and in old-world monkeys, while terrestrial groups had higher

ECIs than arboreal groups, differences in diet were not significant.[18] Furthermore,

terrestrial old-world monkeys had larger troop and individual home ranges than

arboreal ones. Therefore, based on the extra-cortical indices, Sawaguchi divided the

anthropoids (excluding the apes due to a small sample size) into three grades: (1) the

old-world terrestrial/ frugivorous/ polygynous monkeys; (2) both old and new world

arboreal/ frugivorous/ polygynous monkeys; and (3) the new-world arboreal/

frugivorous/ monogynous monkeys.

RSN, as formulated in Sawaguchi (1992), although potentially confounded by body

size effects, is theoretically an appropriate measure of neocortical expansion (Barton

1993). "Neocortical size relative to residual brain size is related to the allocation of

brain material to neocortical functions." However, the exact neuroanatomical

components reflected by this measure are not yet known (Sawaguchi 1992). With

respect to RSN, frugivores displayed higher values than foliovores (contradicting the

ECI based finding (1989)), and values for polygynous and monogynous species did

not significantly differ. Within the frugivores, however, polygynous species exhibited

higher values than monogynous ones. Habitat played no significant role, but troop size

was significantly related to RSN.

These results suggest that the factors controlling primate neocortical expansion are not

uniform across the order and vary in their strength according to the nature of the

animal's environment. This conclusion, that the salience of different factors would

depend to a large extent on the interplay between factors in an animal's environment,

has too often been overlooked by researchers who tend to lump many primates

together without adequately controlling for potential confounds and thus inadvertently

test more than one variable at a time, invalidating the results. Sawaguchi (1992)

emphasizes this interaction between factors and also delineates the limitations of gross

measures of brain function in attributing causal relations stating that intelligence is an

amalgamation of different processes:

Both diet and social interactions appear to be associated with the degree of neocortical

development in anthropoids. The anthropoid neocortex consists of multiple, parallel

circuitries which are involved in multiple parallel functions...Problems arising from

foraging may differ from those associated with social interactions, and different

neocortical circuitries may be responsible for solving different problems...It is,

therefore, likely that multiple, parallel factors associated with diet and social

interactions may have been associated with the development of multiple, parallel

neocortical circuitries of anthropoids.