NEUROBIOLOGY AND THE QUEERNESS OF KINSHIP 103the neurobiology of social behavior because different subspecies of voles
have extremely different social propensities. Like most birds, but unlike the
vast majority of mammals, prairie voles are considered to be monogamous.
They are described as devoted partners, bonding after a single mating and
sharing the parenting of offspring. Animal behaviorists believe that 90 per-
cent of adult prairie voles form long- term pair bonds with a single mating
partner (researchers rarely address the 10 percent who do not pair bond).
Eighty percent of these reportedly do not pair again after loss of a mate.
Prairie voles also coparent, and do so for comparatively long periods. In the
lab, pairs strongly affiliate with each other, and when separated, they exhibit
symptoms of depression (Bosch et al. 2005; Ophir et al. 2008). Because of
their apparent devotion, prairie voles are understood in animal research
as models of monogamy. By contrast, montane voles are observed to have
indiscriminate sex and no long- term bonds, and they are not biparental.
Montane males reportedly do not tend to pups, females affiliate with them
only immediately after parturition, and both sexes are generally less social.
In the early 1990s Tom Insel and Lawrence Shapiro (1992) proposed a
neurobiological explanation for this difference. They hypothesized that the
behavioral disparity was due to differences in the oxytocin system. By look-
ing at postmortem brain slices stained with radioactively labeled oxytocin,
they found differences between the two types of voles in the density of oxy-
tocin receptors in two areas of the basal ganglia. These areas are thought to
participate in what are considered the reward (dopaminergic) and fight- or-
flight (stress hormone) systems of the brain. Insel and Shapiro found that
the montane voles had far fewer oxytocin receptors than the prairie voles.
They found similar differences in vasopressin.^4 In further studies Insel and
Shapiro modified the availability of oxytocin in prairie voles and observed
changes in behavior. They reported that prairie voles whose oxytocin re-
ceptors were chemically blocked behaved more like montane voles, mating
but not establishing partner preferences, whereas prairie voles injected with
oxytocin showed long- term bonding even when they were prevented from
mating. They concluded that oxytocin “appears to be both necessary and
sufficient for partner preference formation, the first step in the develop-
ment of a pair bond in this monogamous species” (Insel et al. 1997, 34).
What relevance do studies of voles have for understanding human kin-
ships? Like 95 percent of mammals, humans are not considered a monoga-