Social grooming
These evolutionary advantages may come in the form of health benefits including reduction in disease transmission and stress levels, maintenance of social structures, and direct improvement of fitness as a measure of survival.
Hence, the fact that animals, particularly primates, groom each other more frequently than necessary from a hygienic standpoint suggests that the social aspect 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 and how much a primate grooms itself (autogrooming), allogrooming involves longer periods of time and different techniques, some of which have connotations of being affectionate gestures.
In many species, individuals form close social connections dubbed "friendships"[8] due to long periods of time spent together doing activities.
[11] In addition to primates, animals such as deer, cows, horses, voles, mice, meerkats, coatis, lions, birds, and bats also form social bonds through grooming behavior.
[13] A 2016 study by Kumar et al.[13] chemically analyzed these secretions, concluding that they may be required in chemosensory mediated communication[14] and mate choice.
Social grooming is critical for vampire bats especially, since it is necessary for them to maintain food-sharing relationships in order to sustain their food regurgitation sharing behavior.
One such study, which collected 16 years of behavioral data on wild baboons, highlighted the effects that sociality has on infant survival.
Social bonds established by grooming may provide an adaptive advantage in the form of conflict resolution and protection from aggression.
[25] In the yellow baboon, adult females form relationships with their kin, who offer support during times of violent conflict within social groups.
These social relationships serve to aid cooperation and facilitate protection against combative groups composed of other males, which can oftentimes cause physical harm.
[30] It is often questioned why the behavior persists if it is costly to the one performing it; however, Charles Darwin proposed group selection as the mechanism behind the clear advantages of altruism.
[32] This tradeoff has been compared to the Prisoner's Dilemma model, and out of this comparison came Robert Trivers' reciprocal altruism theory under the title "tit-for-tat".
This action is reciprocated on other group members (non-mother or of a different rank) more often once the individual is a fully developed adult and can follow normal grooming patterns.
[40] This mimicry is suggested to indicate identification-based observational learning in infant stump-tailed macaques, and the daughters' penchants for maternal mimicry and kin-biased grooming versus the sons' penchants for rank-biased grooming falls in line with their social roles in groups, where adult males require alliances in order to gain and maintain rank.
[43] The wide working memory capacities and causal understanding capabilities of primates permit them to fashion and utilize tools far more extensively than other non-human animals.
There exists a wide array of socially grooming species throughout the animal kingdom, including primates, insects,[45] birds,[46] and bats.
The driving force behind mammalian social grooming is primarily believed to be rooted in adaptation to consolatory behavior as well as utilitarian purposes in the exchange of resources such as food, sex, and communal hygiene.
[56] Grooming in primates is not only utilized for alliance formation and maintenance, but to exchange resources such as communal food, sex, and hygiene.
Grooming activity in these regions is used to remove parasites, dirt, dead skin, and tangled fur in order to help keep the animal's health in good condition despite the individual's inability to reach and clean certain areas.
For example, the article states, "Cognitive constraints and predation pressure strongly affect group sizes and thereby have an indirect effect on primate grooming time".
[60] Horses engage in mutual grooming via the formation of "pair bonds" where parasites and other contaminants on the surface of the body are actively removed.
This behavior seen in cows may provide advantages including reduced parasite loads, social tension, and competition at the feed bunk.
Studies in macaques have shown that increased social stress results in glucocorticoid resistance, further inhibiting immune function.
[73] In the study on neonatal rats, it was found that the receptor number was altered due to a change in both serotonin and thyroid-stimulating hormone concentrations.
An increase in the number of receptors might influence the amount of negative feedback on corticosteroid secretion and prevent the undesirable side effects of an abnormal physiologic stress response.
Studies have also shown that male baboons who participate more in social grooming show lower basal cortisol concentrations.
[75] Faecal glucocorticoid (fGCs) is a hormone metabolite associated with stress that is seen to be present in lower levels in female baboons with stronger, well-established grooming networks.
Endogenous opioids are chemical molecules produced in the brains of organisms that serve to create feelings of relaxation, happiness, and pain relief.
As a result, the literature does not provide a well-rounded idea of what the cognitive or behavioral basis for social grooming is, nor does it completely outline all of its effects, positive or negative.
