Chimpanzee Grooming

Grooming, the act of tidying, cleaning, or brushing oneself or another, occurs  in both chimpanzees and humans. In fact, grooming is seen in all primates, though it is performed differently within each species. Chimpanzees grooming involves removing pieces of dirt, plants, dried skin, and insects from the hair of another chimpanzee of off of themselves. Our own human grooming may involve showering or bathing, cutting or styling our hair, getting a manicure or pedicure, cleaning your ears, or maybe even an exfoliating massage.

Even though there are differences in the way we groom they still achieve the same purpose of cleanliness as well as relaxation and even bonding. Think of time when you picked a piece of fuzz or other small particle from your own or someone else's clothes or hair or how relaxing it is to have someone rub your back. This is just like what chimpanzees do! 

 

The most obvious purpose of grooming in the chimpanzee is the removal of unwanted debris from their coats. But, during times of relaxation, a chimpanzee may often be found grooming another chimpanzee or its own hair. When we want to relax, we often take a bath or get a massage. Just think, grooming is associated with relaxation in chimpanzees and in us! Normally, the chimpanzee uses one hand to hold the hair back while the other hand, lips, or teeth are used to pick out and remove the unwanted small pieces.

 

Grooming is a very important social interaction for chimpanzees and is used to maintain friendly ties among family and community members.

 

 A chimpanzee may request to be groomed by approaching another chimpanzee and presenting a part of his or her body for grooming.  A grooming session may include several individuals of different ages and genders, and can last for a few seconds, minutes, or even hours! Both chimpanzee and human mothers groom their infants.

 

In chimpanzees, this is sometimes done to reduce the stress of infants during weaning (the process of gradually changing the infant’s diet from the mother’s milk to an adult diet). Can you remember a time when you were young and something made you stressed or upset?  It is possible that your mom may have calmed you down through physical contact by rubbing your back or wiping your tears away. Chimpanzees use grooming to reassure each other as well.  Grooming is used to relax tension from threats and aggression in chimpanzees and may be used as a way to make up after a conflict and strengthen the relationship for the future.

 

Social grooming in chimpanzees can serve other functions as well. For example, a chimpanzee who had previously been groomed by another chimpanzee will be more likely to repay that favor in the future, either by grooming or sharing food. This means that in chimpanzees and in humans, if we do something nice for another, that individual is likely to do something nice for us. This is called reciprocal altruism.  

 

For humans and chimpanzees, both males and females are involved in grooming. However, grooming plays a special role in the lives of chimpanzee males and their dominance hierarchy.  Studies show that large males rely more on physical attacks than other techniques to dominate other chimpanzees. Small males rely on grooming other male and female chimpanzees to gain their support and remain in good standing within the community. This helps the less dominant males form alliances to guard against larger males. As a result of these behaviors, smaller males tend to groom more often than larger males that do not need support from others.

 

Grooming is a large aspect of chimpanzee culture. Culture refers to the behaviors or ways of living of a particular group that can be passed from one generation to another. Although all humans and chimpanzees groom, different groups, often located in different parts of Africa, may perform it differently. 

 

One example is the “social scratch” shown by the Mahale chimpanzees. The grooming chimpanzee runs their hand up and down another’s back. This is usually done with bent fingers and making long movements up and down. Chimpanzees living in Ngogo also do the social scratch, but they use straight fingers and make short movements up and down. These two groups are the only which have been observed  performing the “social scratch”.

Another is called the  “handclasp” seen only in the chimpanzees that live in the Mahale Mountains. Each of the chimpanzees extends their arms overhead at the same time and then grasps the other’s wrist or hand. The opposite hand is used to groom the other chimpanzee.

The chimpanzees of Mahale and Gombe make two sounds called lip smacking and teeth clacking, when grooming other individuals. These sounds are accompanied by rhythmic lip movements. If a grooming chimpanzee finds something interesting, the chimp may smack its lips or clack its teeth and immediately bring its mouth to the object. Although the chimpanzees of Ngogo sometimes lip smack and teeth clack, they make entirely different grooming sounds from the chimpanzees in Gombe and Mahale. The Ngogo sound is called sputtering and they do not show rhythmic lip movements.

The chimps at Gombe use leaves to squash small bugs that they pulled from one another’s coats. Scientists believe the chimps started doing this for one of two reasons: because the leaves made it easier to kill the insects or because the chimps did not like getting their hands messy! After this amazing behavior was discovered in the Gombe chimpanzees, it was also observed in Mahale and Kibale. Unlike these chimps, Tai chimps remove the insects, place them on their arm, smack them with their hand, and then eat them!

 

The grooming behaviors discussed here are unique to the particular groups, and, at first, were seen among only a few chimps but now  are seen in generation after generation throughout an entire chimpanzee troop. Group members get these skills through a social learning process. A variety of other cultural behaviors are seen in chimpanzees. 

 

 

Message from CAC'ers

When we were in Tanzania, we had the pleasure of getting to watch chimpanzees grooming each other on more than one occasion.  We could not help but notice how calming and friendly it seemed. In fact, one time we came upon a group of chimps sitting on the trail surrounding a female that appeared to have something stuck in her bottom.  A number of chimps gathered around trying to pick it out for her. Those are some awfully nice friends and family members, would you do that for a friend?!

 

CAC is a program of the Institute for the Study of Human-Animal Relations at Canisius College in Buffalo, NY.