Primates adjust grooming to their social environment
(PHYSorg.com Biology)

Working together and exchanging services for the benefit of everyone involved is crucial for humans and partly responsible for our success as a species. In order to achieve a goal, we need to choose the best possible cooperation partners. Yet who qualifies as the best possible partner depends on the task at hand, the abilities of all available candidates, and on our social relationships with them. Like humans, many non-human primates live in close-knit social groups. Individuals cooperate with each other to their mutual benefit, and often by exchanging services.