Why monkeys groom each other

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Homepage Newsroom Research News Apes and monkeys adjust grooming behavior to their audience. Primates adjust grooming to their social environment Not only the attractiveness of a potential grooming partner matters to wild chimpanzees and sooty mangabeys, their choice also depends on who is observing them.

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Scientists risk overestimating numbers of wild bonobos June 30, Grooming not only removes external parasites, it leads to tolerance, social support, mating advantage and bonding between individuals within a social group.

Grooming reduces tension by lowering the heart rate and releasing endorphins that are calming. It is used to reinforce male-female mate bonds as well as same sex friendship bonds. For example, the length of time macaque and capuchin females groom each other depends on their social rank.

Higher ranked females receive more grooming. Chimpanzees often have bouts of allogrooming that go on for hours when reunited with old acquaintances. They also do it to calm emotions following aggressive outbursts by angry adult males.

So one reason allogrooming is adaptive for the groomer is because they receive the hygienic benefits of being groomed themselves. There may also be other forms of direct reciprocation, such as immediate reduction of aggression, sharing of resources, or assistance in a conflict.

Social bonding between grooming individuals may also be a form of direct reciprocity. While the benefits of the bond may not seem "direct," the bonding is a "response" from the receiving animal Ventura et al. It has been observed within primate groups that individuals generally must give allogrooming in order to receive it and that there is, in fact, a significant correlation between the amount of grooming given and received by an individual.

This is because of the frequency of direct reciprocation in the from of grooming. Primates may also make different types of vocalization to indicate whether they want to groom or be groomed, so individuals can communicate their desires and assess others' intentions. A study on female Japanese Macaques Macaca Fuscata indicates that grooming individuals may use soliciting postures after a certain time has passed to signal the recipient that it's time for the groomer to be groomed.

These communications allow for effective regulation of reciprocity Muroyama, Reciprocity may function somewhat differently in allogrooming occurring between lower ranked and higher ranked individuals.

There is evidence that a lower ranked individual is more likely to groom a higher ranked individual than an individual with the same or lower rank. When a lower-ranked individual grooms a higher-ranked individual, it generally receives protection and greater acceptance and standing in society in return, rather than, or in addition to reciprocation of grooming.

Any of these responses are beneficial, however, and will increase the groomer's fitness Thierry,