Incest Avoidance

In non-human primates, one important mechanism for incest avoidance is sex-based dispersal. Most primate social groups consist of several breeding females and one to several males. In virtually all groups, breeding males or females leave their natal groups (Pusey & Packer, 1987). Additionally, in primates, there are extended infant and juvenile developmental periods; familiarity during upbringing is a proxy for genetic relatedness. Thus, females and offspring or siblings are not likely to breed. Westermarck (1891) proposed, that for humans, close association during childhood, such as between siblings, reduces sexual attraction later in life. One good example of this in humans is Taiwanese “minor” marriages in the 1800s, where families would arrange marriages by giving their daughters over to the future groom’s family as infants. In “major” marriages, couples would meet right before the wedding (http://www.livescience.com/2226-incest-taboo-nature.html). Minor marriages, compared to major marriages, had far fewer offspring, thus providing some support for Westermarck’s hypothesis.
Jane Goodall, in her longterm field research (1986), showed that females and their male offspring and siblings hardly ever mated. Kuester et al. (1994) examined Barbary macaques; they found that matings between paternal kin were more frequent than those between maternal kin. However, they found that these matings rarely led to viable offspring.
One possible biological mechanism for incest avoidance is the major histocompatibility complex (MHC). The MHC are cell-surface molecules that control immune function; MHC molecules bind to protein fragments from pathogens and display them on the cell surface for recognition by immune cells (Jordan & Bruford, 1998). Similarity in the MHC, for humans, mediates such things as organ transplant rejection. Mating with an MHC-dissimilar individual would reduce the risk of mating with a relative; thus, one would expect primates and other animals to choose MHC-dissimilar mates (Grob et al., 1998). One study looked at MHC haplotypes in human mate choice in 411 Hutterite couples (North American isolated reproductive group of European ancestry). The researchers found fewer matches between MHC haplotype between spouses as expected using the geneology of the 411 couples and population genotype frequencies (Ober et al., 1997), providing support for the notion that MHC genotype plays a role in selection of non-related mates.
Another proposed biological mechanism of incest avoidance is through olfactory-mediation kin recognition (Boulet et al., 2009). Boulet et al. (2009) sampled labial and scrotal secretions from female and male ring-tailed lemurs throughout their different reproductive seasons. They found, using a combination of microsatellite and biochemical makers, that during the competitive breeding season, the odor profiles of related individuals converged. Thus, olfactory cues could provide a biological basis for rejecting related mates. Other animals, such as birds, also prefer non-related mates (Bateson, 1978). Bateson showed that male quail individuals prefer to mate with unfamiliar females, not with those that they were raised with.