Grooming and the Evolution of Language

Robin Dunbar’s interesting book, Grooming, gossip and the evolution of language (Dunbar 1996) proposes that language evolved in our primate progenitors as a social bond to promote group cohesion, essentially replacing social grooming. I’m not so sure.

His idea was that social grooming (which in primates goes well beyond that needed for health, for example, to remote ticks and fleas) evolved as societal “glue,” but became inadequate when group sizes became too large. Primate societies are based on relationships, which are usually hierarchical: whom you groom, who grooms you, both determine and demonstrate your place in society, which in turn determines your personal and consequently reproductive success. Hence, it is an evolutionary adaptation. But you can only groom and be groomed by so many partners. Beyond a certain group size, grooming becomes inadequate. Dunbar showed, based on a variety of paleontological, anthropological and physiological data and modern and extinct primates, including humans (for example, predicted group size based on ratio of group size to neocortex in primates) that group sizes grew from about 60 in australopithecines, to 80 in H. habilis, 100-120 in H. erectus, 110-130 in archaic humans, and 120-160 in modern humans. Modern human group size, whether as hunter-gatherers, military legions, or corporate operating units, is amazingly consistent and seems related to the number of people that anyone can know personally.

Anthropologist do generally agree that our brain size grew to primarily accommodate the memory and analytical processing power needed to keep track of all the relationships in increasingly larger groups: from 450 cm3 in A. africanus to 750 cm3 in H. habilis, 1050 cm3 in H. erectus, and 1350 cm3 in H. sapiens (Pilbeam and Gould 1974). However, absolute size is not the whole story: in modern humans, body size was reduced somewhat, while the brain stayed the same or grew a little, meaning that relative brain size continued to increase and the biggest jump in relative brain size was only 100,000 years ago (Kappelman 1996). By Dunbar’s reasoning, therefore group size should have reached its peak then, not in archaic humans. This is, not surprisingly, around the time that most anatomists (if not linguists, who favour a later date) that language with complex evolved.

Dunbar reasoned that since gossip and other social commentary forms the bulk of human conversation—more, for example, that practical matters such as where to hunt kudu or when to propose a corporate merger—that it must have evolved as a replacement for grooming. He dismissed the previous notion, still held by many anthropologists, that language began as a way to communicate practical matters essential to survival, such as how to stalk a dangerous prey or warning of a predator.

But humans have a very different vocalization apparatus, including the shape and position of the hyoid bone, that lets us make a much wider range of sounds than any other primate, and this must have evolved much longer ago than the last 100,000 years. And even monkeys make a sufficiently wide range of vocalizations combined with commonly understood meanings, to give and distinguish among different warning calls for different predators. For example, vervet monkeys (pictured above) and many other colobine monkeys have give warning calls that distinguish among snakes, eagles, and leopards; in mixed species groups, all species of monkeys recognize and respond appropriately to each of the warning calls that the other species give. Surely, the roots of human language are much older than the beginning of larger group sizes.

Here’s how I think language started, and why I think it. Early in my career as a wildlife biologist, I worked with several Inuit and Dene (First Nations aboriginal people of Canada) hunters and trappers and at times camped with their families, few of whom could speak English. But our work required communication, and it was not long before, in each situation, my native counterparts and I knew each other’s words for the common animals we encountered, a few other nouns such as “track”, and a few verbs such as “hunt” and “follow”. Because I could write and kept notes, I perhaps learned these words more quickly than a hunter-gatherer who could not write. But that we learned, and quickly, shows how important in was for us, and how important it must have been for our hunter-gatherer ancestors. But there is more. My colleagues had a lot of gestures that they used to indicate different animals and verbs such as “hunt,” “track.” and “follow.” And the gestures were different from tribe to tribe. For example, Cree men from the Beaver Indian tribe of northwestern Alberta often pointed with their lips. To indicate where a caribou had gone, they would turn their face in that direction and pucker their lips, as if trying to kiss the direction. Clearly, hunters need non-verbal “words” so that they can coordinate a hunt without alerting the prey.

Archaeological evidence suggests that, since both H. neandertalensis and H. sapiens could speak, then their common ancestor, H. heidelbergensis, could, too. Rudimentary speech as described above: nouns describing everyday objects, no doubt dates from that time. Experts are divided as to when grammatical language with syntax developed, but estimates range from 300,000 to 50,000 years ago (see review in Ambrose 2001). This happened long before the development of modern humans.

Recent genetic evidence shows that we lost our hair at least 1.2 MYA(Rogers et al. 2004) , while archaeological evidence shows that we began using scraped hides as clothing about 300,000 years ago, and adopted sewn, well-fitting clothing around 20,000 years ago (see review in Rantala 2007). Language therefore coincides roughly with adoption of clothing, but not with nakedness. Since grooming would have been basically unnecessary for hygiene between 1.2 and 0.3 MYA, and it’s not possible to “groom” naked skin, it seems that Dunbar’s thesis is untenable. No, language started, if not with hunting per se, then with the general need to communicate about the exigencies of life among our ape ancestors who cooperated and coordinated their activities.

References
Ambrose, S. 2001. Paleolithic technology and human evolution. Science 291:1748.
Dunbar, R. 1996. Grooming, gossip and the evolution of language. Harvard University Press, Cambridge, Massachusets.
Kappelman, J. 1996. The evolution of body mass and relative brain size in fossil hominids. Journal of Human Evolution 30:243-276.
Pilbeam, D., and S. J. Gould. 1974. Size and scaling in human evolution. Science 186:892-901.
Rantala, M. J. 2007. Evolution of nakedness in Homo sapiens. Journal of Zoology 273:1-7.
Rogers, A. R., D. Iltis, and S. Wooding. 2004. Genetic variation at the MC1R locus and the time since loss of human body hair. Current Anthropology 45:106-108.