Rarely in the history of biology has a domain of empirical
knowledge followed so closely and fruitfully upon an abstract
theoretical idea. —E. O. Wilson (Kin Recognition: An Intro-
ductory Synopsis, 1987)
T
he “abstract theoretical idea”to which
Wilson refers is, of course, W. D. Hamilton’s (1964)
theory of inclusive fitness, which specifies the con-
ditions under which an allele would change frequency in a
population due to its effects on its bearer’s reproduction
and the reproduction of its bearer’s collateral relatives like
siblings, nieces, and nephews. Hamilton knew that if kin-
ship were to mediate social relationships, whether coopera-
tive or competitive, then individuals must possess the means
to identify kin, and he outlined four proximate means by
which kin could be identified (Hamilton 1964). The impor-
tance of parent-offspring recognition and its relevance to
discriminative parental care was well known prior to Ham-
ilton’s theorizing, but in the late 1970s papers began to ap-
pear on the recognition of collateral kin, and various spe-
cies of rodents were often the study organisms described in
these papers (reviewed in Blaustein et al. 1987; Dewsbury
1988; Holmes 2004).
We have three aims in this chapter. First, we will exam-
ine some of the conceptual and methodological issues that
characterize the kin-recognition literature. Second, we will
use a model-systems approach to review some of the pri-
mary empirical findings on rodent kin recognition, such as
the sensory basis of recognition and the role of early expe-
rience in the ontogeny of recognition. Finally, we will out-
line some questions and issues about rodent kin recogni-
tion that we believe should be pursued in future studies. We
discuss kin discrimination as a process that facilitates nep-
otism (preferential treatment of kin), which historically has
been the focus of research on rodent kin recognition. We
also note, however, that the issues we address apply to mate
choice, as animals evaluate their relatedness to potential
mates and avoid the deleterious effects of extreme inbreed-
ing and outbreeding.Conceptual and Methodological IssuesThe meaning of kin recognition
Throughout most of the 1970s and 1980s, kin recogni-
tion referred to an internal physiological process that was
inferred from kin discrimination, the differential treatment
of conspecifics based on unambiguous and reliable (over
evolutionary time) correlates of genetic relatedness (Holmes
and Sherman 1982, 1983). The correlates of genetic relat-
edness are often phenotypic attributes borne by conspecif-
ics, but contextual cues such as spatial locations or time
spent in proximity to a mate (e.g., Davies et al. 1992; Al-
berts 1999) may also correlate with relatedness and under-
lie differential treatment.
It is useful to distinguish between direct(kin) recogni-
tion, which depends on phenotypic attributes like odors
that are borne by individuals (hereafter, “kin labels”) and