How Old is Chimp Culture: Finding the Chimp Y-chromosomal Adam

Some of the chimp cultures currently identified, along with the behaviours practised by each (you’re probably going to want to click to see a bigger image)

Chimpanzee groups have cultures. Over time, each troupe of chimps has invented new ways of doing things and passed on this knowledge to subsequent generations. The results of this can be quite significant differences between the cultures¹. One group might have developed a way to gather a certain sort of food inaccessible to another species. Or another group might have developed spears. But just how long did it take for all these cultural differences to accumulate?

One aspect of chimp behavior which doesn’t change may hold the key: patrilocality. In the eastern sub-species of chimp (Pan troglodytes schweinfurthii) the males stay in the group they were born in. It’s the lady-chimps who leave the group and find a new home when the mature, preventing genetic stagnation. The only time the males leave the group is if it grows to large; causing the group to cleave in two. As such the male family tree for these chimps would mirror the family tree of the groups².

Building on this fact, a team of researchers examined the Y chromosome of 273 male eastern chimps from 8 groups (all gathered from faecal samples). They then used the genetic divergence between these chromosome to calculate how much time has passed since the most recent common ancestor of all male eastern chimps; and thus the maximum amount of time the groups have been isolated². Those of you with a keen eye for genetics might recognize that this method has been applied to humans to find Y-chromosomal Adam: the last male common ancestor of people. Except profound cultural inferences couldn’t be made from him (aside from our societies ability to misunderstand science).

So just how long did chimp Y-chromosomal Adam (or Chadam, as I shall now be calling him) live? The researchers’ calculations indicated that Chadam lived at some point between 125 – 2625 years ago². This is particularly notable because even the highest estimate is almost half the age of the Panda 100 site: a location where chimps have been cracking the same nuts with the same sorts of tools for 4,300 years. In other words, archaeologically speaking there appears to have been cultural stasis yet during this period 8 eastern chimp cultures developed³.

This has some significant implications for human evolution as well (you knew it was coming eventually, this is a blog all about human evolution after all). The earliest stone tool technology our ancestors made also appear to have remained unchanged for hundreds of thousands – if not millions – of years⁴. But if these results are anything to go by, this period of apparent technological stagnation could’ve actually been a very vibrant and innovative time for early humans.

References

1. Whiten, A., Goodall, J., McGrew, W. C., Nishida, T., Reynolds, V., Sugiyama, Y., … & Boesch, C. (1999). Cultures in chimpanzees. Nature, 399(6737), 682-685.
2. Langergraber, K. E., Rowney, C., Schubert, G., Crockford, C., Hobaiter, C., Wittig, R., … & Vigilant, L. (2014). How old are chimpanzee communities? Time to the most recent common ancestor of the Y-chromosome in highly patrilocal societies. Journal of Human Evolution.
3. Mercader, J., Barton, H., Gillespie, J., Harris, J., Kuhn, S., Tyler, R., & Boesch, C. (2007). 4,300-year-old chimpanzee sites and the origins of percussive stone technology. Proceedings of the National Academy of Sciences, 104(9), 3043-3048.
4. Stout, D., Semaw, S., Rogers, M. J., & Cauche, D. (2010). Technological variation in the earliest Oldowan from Gona, Afar, Ethiopia. Journal of human evolution, 58(6), 474-491.