“Affiliative Behavior of Related and Unrelated Pairs of Cats in Catteries: a Preliminary Report”, 1999-04-23 (; backlinks; similar):
Social ties between free-ranging cats are largely confined to related females, yet multicat households often contain unrelated cats. We have investigated whether unrelated pairs of cats from the same household are less affiliative towards one another than pairs of littermates, by observing their behavior while confined in catteries. We found that littermates spent more time in physical contact with one another, groomed one another more often, and were more likely to feed close to one another than unrelated cats. The most likely explanation for this difference is that ties are established between individual cats during the socialisation period (3–8 weeks), and persist throughout life if the cats continue to live together.
[Keywords: cat kinship, social behavior, socialisation, spacing behavior]