Phylogeny refers to evolutionary history behind the development of a taxon or trait.  Here we address the phlogeny of the primate taxon and the transition of allogrooming (social grooming) from its hygienic  function to its social function.

Evolution of Primates


Primates probably evolved about 60 million years ago, monkeys about 30 million years ago, and apes about 14 million years ago.  The first primates were squirrel-like creatures.  They evolved hands and feet which were better for grasping and manipulating objects, stereoscopic vision, and larger skulls and more errect posture, probably in that order. 

The development of larger skulls corresponds with the evolution of more intelligent primates, particularly monkeys.  The increase in intelligence allowed for more complex social interactions, while the social challenges of living in larger groups is thought to be the main driving force behind the continued development of higher intelligence.  The increase in social complexity probably coincided with the change of allogrooming's function from purely hygienic to social(Kappeler, 2002).


Figure 4. Phylogenic tree of evolution of modern primate species.(

Evolution of Allogrooming

Social Grooming is a behavior exhibited by an extremely diverse population of animals, including insects, fish, birds and mammals, and how the behavior first developed is unknown.  Typically it has a hygienic function; being groomed is good for an animal's health and general functioning and hence increases fitness.  Some grooming practices are better performed by another and hence if there is a mechanism to regulate reciprocal exchange of allogrooming, it will develop as an evolutionarily successful behavior (Korstjens, 2002).

Its Purpose in Primate Society

Grooming in primates is unusual in that it serves an important social function, while hygiene seems to be a secondary function.  The social circumstances of many species of primates' lives require a way of sustaining and regulating complex social interactions so as to foster productive social behaviors and cooperation.  Social grooming is thought to be the tool which serves this purpose in these groups of primates.  It would have made an evolutionary transition from its hygienic purpose to its social purpose as primates began to live more cooperatively in large groups (Hutchins and Barash, 1976). 

Connection to Language

There is also evidence of and a strong consensus across disciplines that social grooming is the likely functional, phylogenic, precursor to language in humans.  While allogrooming is an effective way for smaller groups to socialize and bond, it would become impractical for larger groups because of the time cost it would entail.  Thus, while there were evolutionary incentives for larger groups than grooming could effectively maintain, the cheaper alternative of language evolved to allow for more creatures to maintain social bonds without spending huge amounts of time and energy on it.  According to Robin Dunbar, human beings with our current language capacities can effectively maintain social ties to 150 people at once, whereas if grooming were used as the method of bonding, this would take approximately 42% of each individual's time, which is almost certainly unsustainable under selective forces (Dunbar, 2008).