The old saying, blood is thicker than water, holds true in many species where related animals are treated differently from non-related ones. When interactions between individuals are influenced by their genetic relatedness, it is known as kin discrimination.

Scientists believe this discrimination is a way to prevent inbreeding, and aid in the survival of kin who then pass shared genes on to their offspring. In order to discriminate kin, animals need to recognize one another. It is not so difficult to identify those who share a nest or territory as kin, but how do animals identify unknown individuals?

Scientists studying rodent species have found that odor is an important cue. Urine in rats and mice contains many chemical by-products produced by a set of genes know as the major histocompatibility complex. These genes appear to be good indicators of how related individuals are to one another.

Many species, such as beavers and squirrels, have glands that produce additional odors. Belding's ground squirrels produce at least two odors from oral and dorsal glands. They are able to determine very small differences in relatedness with these odors. For example, they can identify a cousin from non-kin or a grandmother from an aunt.

This is important because relatedness influences their social behavior. Full sibling juveniles spend more time playing and sleeping with each other than three-quarter siblings or non-siblings. It is believed these initial interactions set the groundwork for adult associations that aid in survival, such as alarm call frequency, territory defense, and sharing of hibernation dens.