Intern Owen: Special Topic
A social tradition is defined as a “behavioral practice that is relatively long-lasting and shared among members of a group, each new practitioner of the behavior relying to some extent upon social influence to learn to perform the behavior”. Some of these traditions may work to increase foraging success or strengthen social bonds, but some have no clear evolutionary purpose at all. A group of 10 capuchin field researchers worked together to identify and understand social traditions in capuchins. They focused on 4 different research sites in Costa Rica (Santa Rosa National Park, Lomas Barbudal Biological Reserve, Palo Verde National Park, Curu Biological Reserve), which contained capuchin groups that were geographically and ecologically similar enough to suggest little genetic difference. This allowed them to delve into the development and social transmission of these unique behaviors.
The traditions were identified and classified based on the following 3 criteria:
1. The behavior must occur at least once per 100 hours in one or more group and be absent in other groups to be considered common, once per 250 hours to be rare.
2. The behavior must be observed to spread through a social network.
3. The behavior must continue being displayed for at least 6 months.
In the Lomas Barbudal Biological Reserve, 5 social traditions were observed over a 13-year period: Hand-sniffing, Eyeball-poking, Sucking of body parts, Hair-in-mouth Game, and Toy Game.
Hand-sniffing was observed to have 2 variations: 1) the hand of one individual is wrapped around the nose and mouth of another; 2) the fingers of one individuals are inserted into the nostrils of another. The participants performing the behavior would maintain the position for several minutes, often swaying as they sniffed. This was commonly observed to be a mutual behavior in which both participants would be Hand-sniffing each other. This tradition was common in 4/7 groups, rare in 1/7, and absent in 2/7.
Eyeball-poking involves one individual inserting a finger between another’s eyelid and eyeball, up to as deep as the first knuckle. The participants usually maintain the behavior for several minutes, but some sessions have been observed to last up to an hour. If the finger falls from the eye it is often reinserted. It was observed that the recipient of the Eyeball-poking would often insert a finger into the actor’s mouth or nostrils during the process. This tradition was common in 0/7 groups, rare in 4/7 groups, and absent in 3/7.
Sucking of body parts involves one participant inserting some body part of another participant (tail, finger, ear etc.) into its mouth and sucking for several minutes. Both participants often mutually perform this behavior; especially in cases when the tail tip is the body part being sucked. Participants are often slightly apart from the rest of the group, relaxed, and groom each other before performing this behavior. This tradition was common in 2/7 groups, rare in 3/7 groups, and absent in 2/7 groups.
Hair-in-mouth Game involves one participant biting hair from the face or upper body of another. The other participant may flinch, but then will try and retrieve the hair by attempting to open the mouth of the partner. If successful, the hair is then passed between the partners’ mouths until the majority of it has fallen to the ground. If one participant begins to lose interest, the other may open his or her mouth to show how much hair remains. This tradition was common in 2/7 groups, rare in 1/7, and absent in 4/7 groups.
Toy Game functions in much the same manner as the Hair-in-mouth Game, except an inanimate object is used instead of hair. This object is often a stick, a leaf, or a piece of bark. As with the Hair-in-mouth Game, the toy is never consumed, but transferred between each participant’s mouths until it falls to the ground. This tradition was common in 2/7 groups, rare in 1/7, and absent in 4/7.
These traditions show no evidence of evolutionary advantage – some even seem to pose high risk to the participants. However, they persist for a significant duration of time; anywhere from 6 months to 10 years. It is theorized that these behaviors exist in a similar way to human fashion trends; they arise, socially transmit and then fade, without any significant effect on survival or reproduction. These trends, however, may work as a mechanism for social bonding that can reduce conflict and increase cohesion as a group. They may help solidify alliances, reduce stress, or even be a symptom of social learning. Either way, social traditions in capuchins are fascinating.
At PPS, we see the resident capuchins, Miracle and Prospero, displaying unique behaviors that could be social traditions. One example is when they gather small rocks onto their platforms and arrange them into different orders. There is no clear evolutionary benefit to this behavior, and yet it persists. It mainly occurs during early mornings before they have been fed, suggesting this tradition may function as a process that occupies them until their food arrives. As capuchins naturally combine substrates and are extractive foragers, this type of behavior may be an immersive game to them. The highly social nature of capuchins, combined with their high cognitive functioning, results in a variety of unique and quirky traditions to occur – just like in us humans.
References:
· Balter, M. "Probing Culture's Secrets, From Capuchins To Children". Science, vol 329, no. 5989, 2010, pp. 266-267. American Association For The Advancement Of Science (AAAS), doi:10.1126/science.329.5989.266.
· Fragaszy, Dorothy M et al. The Complete Capuchin. Cambridge University Press, 2004.
· Perry, Susan. "Social Traditions And Social Learning In Capuchin Monkeys (Cebus)". Philosophical Transactions Of The Royal Society B: Biological Sciences, vol 366, no. 1567, 2011, pp. 988-996. The Royal Society, doi:10.1098/rstb.2010.0317.
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