S

ocial groups of related females typify several mam-
malian species. These kin-based groups are found par-
ticularly in primates and rodents, and occur in other
orders as well. Kin groups are associated with particular
mating and dispersal patterns, usually polygynous mating,
philopatry of females in the natal social group, and male
dispersal away from the natal group (Greenwood 1980;
Dobson 1982). Groups of closely related individuals are a
necessary condition for the evolution of cooperative behav-
ior via kin selection (Hamilton 1964), and thus mating and
dispersal patterns may influence the evolution of social be-
havior. Kin groups may also create genetic structure within
a population, and thus social evolution may depend on ge-
netic substructuring of populations (Chesser 1998). In gen-
eral, when individuals in social groups are more closely
related, genetic substructuring within the population is
greater, and so is the potential for social evolution.
The purpose of this chapter is to examine both theory
and empirical studies that examine the coevolution of so-
cial groups, particularly kin-based groups, and genetic sub-
structure of local and regional populations. The funda-
mental question is: how much do mating systems, dispersal
patterns, and, especially, social group structure influence
genetic properties of populations? Basset et al. (2001) used
simulations to study two models of genetic substructur-
ing of local populations, and found substantial influences of
mating and dispersal patterns on estimates of gene dynam-
ics. Under polygynous mating and sex-biased dispersal,
their simulations revealed substantial genetic differentiation
among groups within a local population. My goal is to ex-
amine population-genetic theory concerning the gene dy-
namics of kin-based social groups and point out some of the

differences between the two current models that have been

used to study some aspects of gene dynamics. I will also ex-

amine empirical evidence in rodents and other small mam-

mals that focus on whether kin-based social-genetic sub-

structuring occurs within local populations.

Models of Gene Dynamics

How might we determine the degree of genetic substructure

that is associated with kin-based groups? The answer to

this question was provided by Sewell Wright (1965, 1969,

1978). He devised measures of genetic properties, or gene

dynamics, of populations that were structured into geo-

graphical subpopulations. These metrics compared rates of

inbreeding within and among subpopulations to expecta-

tions from random mating (F-statistics), and also quanti-

fied the rate at which inbreeding accumulates (termed ef-

fective population size). The rate of inbreeding compared to

what would be expected if mating were random among the

members of a subpopulation was termed FIS. The rate of in-

breeding compared to that expected if all the members of a

population were mating randomly was called FIT. The de-

gree of genetic differentiation among subpopulations was

termed FST. I, S,and Tindicate population levels of indi-

viduals, subpopulations, and the total regional population,

respectively. Finally, effective population size was defined

as a function of the relative rate of change in the inbreed-

ing coefficient from one generation to the next (viz., Ne

1/(2 F), the inbreeding effective population size; Crow and

Denniston 1988).

Although Wright’s measures of gene dynamics were de-

Chapter 14Gene Dynamics and Social Behavior

F. Stephen Dobson