Culture defines who we are but few can explain where it comes from or why we adopt one tradition over another. In the classic musical The Fiddler on the Roof the family patriarch, Tevye, muses on this basic fact of human existence:
Here in Anatevka we have traditions for everything... how to eat, how to sleep, even, how to wear clothes. For instance, we always keep our heads covered and always wear a little prayer shawl... This shows our constant devotion to God. You may ask, how did this tradition start? I'll tell you - I don't know.
The origin of particular cultural traits in human populations has long been a mystery to anthropologists. Many societies have responded the same way Tevye did, "it's merely part of our culture, what else do you need to know?" Nevertheless, the maintenance and dissemination of cultural traits remains a fascinating topic that scientists have long struggled to understand. More recently, however, researchers have discovered that humans aren't unique in this regard. Nonhuman primates also have culture and research into how this is transmitted between individuals has recently taken a major step forward.
While nonhuman primates don't have obvious cultural traditions the same way humans do, such as variation in their clothing or adding extra spice to their food, primatologists have nonetheless identified behavioral practices that vary between communities and which are transmitted through social learning. For a behavior to be considered a cultural practice in nonhuman primates it must meet certain conditions: the behavior must be practiced by multiple members of the community, it must vary between societies, and the potential for that same behavior must exist in other societies.
A good example of such a cultural trait was just discovered last year and published in the journal Current Biology (review here). Kibale Forest chimpanzees were found to use sticks to get at the honey in a fallen log, whereas Budongo Forest chimpanzees used chewed leaves as sponges to collect the same thing. Both societies had the same tools at their disposal, but they each chose a different approach. A single individual first used one of these techniques and other members of the group adopted it through imitation and social learning. This is merely the latest example of cultural traditions in different chimpanzee societies.
Cultural diversity in chimps from National Geographic's "New Chimpanzees" (1995)
However, some societies have more unique cultural traits than others. To understand why this would be researchers Johan Lind and Patrik Lindenfors of the Centre for the Study of Cultural Evolution and the Department of Zoology at Stockholm University, Sweden analyzed the demographics of different chimpanzee societies in their paper published in the Public Library of Science. They hypothesized that, since infants so readily imitate their mothers as they're growing up, the number of females within a given society may explain the number of cultural traits. Individuals spend at least eight years in close proximity with their mothers while fathers are scarcely involved. Furthermore, tool use is central in chimpanzee societies and females use tools more frequently than males do. Since chimpanzees are patrilocal (males remain in their natal group while females migrate at puberty) any cultural traits learned by young males would remain in the society while young females would transfer that same trait to nearby societies.
Because females express and transmit more culture than males, and because females transfer between communities bringing with them their cultural knowledge, the number of cultural traits present in any given chimpanzee community should depend on the number of females in that community. Thus, we hypothesize that the number of cultural traits in chimpanzee communities should correlate with the average number of females in chimpanzee communities, but not with the average number of males.
As can be seen in Figure 1 above, the number of societies studied with documented cultural traits is not high (n = 7), however the researchers found a significant correlation between the number of females in a society and the number of cultural traits present (p = 0.010). There was no correlation between cultural traits and the number of males.
This implies that females are critical in chimpanzees for transmitting cultural traits and maintaining cultural diversity. The reported pattern may be explained by the fact that females transfer between communities, bringing with them novel cultural traits and consequently increasing the cultural diversity of the community as a whole.
This is not to say, of course, that there will always be a direct correspondence between the number of females and the number of cultural traits in that society (as can be seen by Mahale M-group), but the evidence is suggestive that there is a pattern of cultural transmission in chimpanzees being driven by females.
The authors point out that the pattern for human societies is different from chimpanzees and that the number of cultural traits increases as the population of both males and females increases. This would appear to demonstrate the important role that fathers play in the social learning of their children. However, as The Fiddler on the Roof reveals all too clearly, new cultural ideas from outside one's community can infiltrate as societies continue to grow. Under such conditions neither mothers nor fathers can maintain a single cultural norm for long.
Lind, J., & Lindenfors, P. (2010). The Number of Cultural Traits Is Correlated with Female Group Size but Not with Male Group Size in Chimpanzee Communities, PLoS ONE, 5 (3). DOI: 10.1371/journal.pone.0009241
Originally published at ScienceBlogs