allogrooming.

A variety of animals, but especially primates, groom one another. There is still some disagreement about the reasons but most agree there is some level of reciprocity and push for social standing. 

In other words, primates pick out dead skin, dirt, lice, and parasites from their primate-friend so that the friend will then return the favor and groom them. At some point. 

And also to increase their social clout. There are fairly complicated hierarchies in most primate communities and grooming allows players to rise up the social ladder, especially depending on whom is being groomed.

Some say that this is exactly what us humans are doing with social media.
Give a like to hopefully get one and further develop social clout.  

You can decide whether you agree or not.
Or whether you should or not. 
Or whether life is more inspiring than an ape's.