Social grooming is a behavior in which social animals, including humans, clean or maintain one another's body or appearance. A related term, allogrooming, indicates social grooming between members of the same species. Grooming is a major social activity, and a means by which animals who live in close proximity may bond and reinforce social structures, family links, and build companionships. Social grooming is also used as a means of conflict resolution, maternal behavior and reconciliation in some species.[1][2] Mutual grooming typically describes the act of grooming between two individuals, often as a part of social grooming, pair bonding, or a precoital activity.
There are a variety of proposed mechanisms by which social grooming behavior has been hypothesized to increase fitness. These evolutionary advantages may come in the form of health benefits including reduced disease transmission and reduced stress levels, maintaining social structure, and direct improvement of fitness as a measure of survival.
It is often argued as to whether the overarching importance of social grooming is to boost an organism's health and hygiene or whether the social side of social grooming plays an equally or more important role. Traditionally, it is thought that the primary function of social grooming is the upkeep of an animal's hygiene. Evidence to support this statement involves the fact that all grooming concentrates on body parts that are inaccessible by autogrooming and that the amount of time spent allogrooming regions did not vary significantly even if the body part had a more important social or communicatory function.[3]
Social grooming behaviour has been shown to elicit an array of health benefits in a variety of species. For example, group member connection has the potential to mitigate the potentially harmful effects of stressors. In macaques, social grooming has been proven to reduce heart rate.[4] Social affiliation during a mild stressor was shown to correlate with lower levels of mammary tumor development and longer lifespan in rats, while lack of this affiliation was demonstrated to be a major risk factor.[5]On the other hand, it could be argued that the hygienic aspect to allogrooming does not play an as important role as the social aspect to it. Observational studies performed on 44 different primate species suggest that the number of times a species allogrooms, on average, correlates with its group size rather than with its body size.[6] If allogrooming was purely required from a hygienic standpoint, then the larger an animal, the more and more often it would be groomed by members of its group. However, we see instead that when group size increases, members ensure that they spend an appropriate amount of time grooming everyone. Hence, the fact that animals, particularly primates here, groom each other more frequently than necessary from a hygienic standpoint suggests that the social angle of allogrooming plays an equally, if not more, important role. Another point of evidence for the importance of the social aspect is that in comparison to how much and how a primate grooms itself (autogrooming), allogrooming involved longer periods of time and different techniques, some of which have connotations of being affectionate gestures.[7]