June 11, 2005

A new idea about the evolution of language

Derek Bickerton has a "blog". I put the word in quotes, and I haven't added it to our blogroll yet, because so far there's only one post, from 3/25/2005. On the other hand, it's a doozy: a 12,000-word paper with 98 bibliographic references entitled "The Origin of Language in Niche Construction."

Derek's theory is that it's all about cutting up dead elephants.

In more sober and scientific wording: Language emerged because of the need to recruit and coordinate crews to help in scavenging the carcasses of naturally-deceased megafauna. On this view, our ancestors "engaged in counteractive niche construction" by turning to scavenging megafauna because

...when woodlands were replaced by grasslands, food sources other than meat (except for tubers, O’Connell et al. 1999) became much more rare. At this point, hominids engaged in counteractive niche construction (Odling-Smee et al., 2003: 46): a process in which a species counteracts an environmental change by relocating to a new environment or changing some aspect of its behavior. The new niche was a logical move for organisms that had already used stones to break open bones and (probably) digging sticks to excavate tubers. All they needed were the flakes struck off in the production of Oldowan tools.

At least by the Plio-Pleistocene boundary hominids had moved their focus from brain and bone-marrow to active scavenging and butchery (Bunn & Kroll 1987 Blumenschine 1987). The efficacy of Oldowan tools was practically demonstrated by Kathy Schick and Ray Dezzani, who used them to butcher an elephant that had died of natural causes (Schick and Toth 1993, pp. 166ff). They "were amazed as a small lava flake sliced through the steel gray skin, about one inch thick, exposing enormous quantities of rich, red elephant meat." Since "modern scavengers normally do not eat a dead elephant until it has decomposed for several days"–they can’t, their teeth cannot penetrate the skin until decay and the expansion of internal gases has split it open–"such carcasses may have provided occasional bonanzas for Early Stone Age hominids" (see also Blumenschine et al, 1994). In fact, the bonanzas may not have been so occasional.

This in turn motivated a "fission-fusion" type of social organization:

On the one hand, the scarcity of good night refuges plus the need for numbers to protect against a mass attack by nocturnal predators of the hyena class would have pushed towards large nighttime group sizes. On the other, the thin and dispersed state of food sources would have pushed towards small daytime group sizes. The optimal solution would have been for nighttime groups of, say, ~50 to split into several smaller groups for daytime foraging, then regroup at the original point of dispersal.

Derek argues that living off the carcasses of nautrally-deceased megafauna

...fulfilled all the conditions requiring recruitment. They were scattered, indeed relatively rare. Their location was unpredictable, except perhaps that in drought seasons they were somewhat likelier to be found around dried-up waterholes. They were highly transient, in that they offered a very narrow window of opportunity between the moment of death and the first rupture of skin. Post-rupture, they would have been highly dangerous, surrounded by hungry and impatient animals in considerable numbers. Indeed, prospective scavengers may have start arriving well ahead of the first rupture, so that the sooner hominids located the carcasses, the better. One thing going in their favor was that predators and scavengers alike are good cost-benefit analyzers. No animal is going to risk being lamed by a well-aimed stone when the feast is a prospect still several hours away (when the carcass is open and ready and you either grab your piece or go hungry, it’s a different story). But the most crucial condition was that the carcasses were sizeable–many times larger than any hominid.

Thus scavenging megafauna rewards cooperation:

The paradigm case for all other primates is that of an animal confronted by a rare and delicious fruit, probably not more than a pound or so in weight, whose possession of it is in no way threatened by any other species–only by other members of its own group. Under such circumstances, selfishness pays off, and the animal will employ any stratagem that allows it to eat undisturbed. Now consider an animal confronted by a rare and delicious carcass, weighing in excess of a ton, whose possession of it is threatened by a variety of very ferocious species. Selfishness is futile here, co-operation is the only way to go; animals that do not co-operate get nothing.

Suppose a small sub-group of hominids, alerted by vultures or just lucky, stumbles on a huge carcass, still unruptured. Possibly other animals are already stalking around. The group could, of course, take its chance and start cutting. But to start cutting would have the same effect as a rupture, it would immediately trigger a feeding frenzy in the other scavengers, and the smells of blood and meat might draw more of them. The whole sub-group could be overrun in minutes and end up as dinner too. Besides, how could they, even if they drove off all other scavengers, eat all that meat by themselves? Some might have close relatives in other sub-groups; inclusive fitness would then also come into play. In other words, almost every factor in the situation would cause them to seek additional helpers...

and the best way to get folks to cooperate is to talk with them:

Unlike ants, hominids did not have any physical mechanism with which to present samples of the food. They did not have the ability to lay chemical trails. They might jiggle about excitedly, but how would this persuade others in their group to drop whatever they were doing and accompany them?

Having a brain the size of a coconut rather than the size of a pinhead has disadvantages as well as advantages. One disadvantage, in this context, is that you are then an individual rather than a cog in a machine; you have your own agenda, your own preferences, and definitely a will of your own. This can only be a thought experiment, but imagine approaching a troop of chimpanzees and bonobos and trying to get them all to do the same thing at the same time. ... Moreover, another subgroup might have made finds of its own (piles of bones, bees’ nests, termite mounds...) that could satisfy more than that one sub-group. The state of mind might often have been: why should I go to your find, why don’t you come to mine? Optimal foraging required some way to express, compare and evaluate the finds of different sub-groups.

Recruitment, therefore, couldn’t happen unless the nature of the find could somehow be indicated. One of the advantages of the coconut-size brain is that it holds primary representations (Bickerton 1990) of a very broad range of organisms and entities, including all the species with which the individual habitually interacts. To express these, all that is needed is a layer of secondary representation: some unique labels that will signify the objects concerned and trigger associations with those objects in the minds of others.

I'm glad to be able to add this to the list of theories of the selective pressures for development of language. Charles Darwin (and more recently Geoffrey Miller) suggested that our ancestors developed language so as to sing more convincing love songs. Robin Dunbar thinks it was because gossip is more efficient than grooming for social group maintenance. Terrence Deacon thinks it's because male provisioning of meat for women and children required a socially-sanctioned symbolic marriage ritual. Now Derek Bickerton argues that it's because efficiently cutting up dead elephants required "some way to express, compare and evaluate" the opportunities found by different scouting parties.

I think that Terrence Deacon's observation still holds:

From the perspective of hindsight, almost everything looks as though it might be relevant for explaining the language adaptation. Looking for the adaptive benefits of language is like picking only one dessert in your favorite bakery: there are too many compelling options to choose from. What aspect of human social organization and adaptation wouldn't benefit from the evolution of language? From this vantage point, symbolic communication appears "overdetermined." It is as though everything points to it. A plausible story could be woven from almost any of the myriad of advantages that better communication could offer: organizing hunts, sharing food, communicating about distributed food sources, planning warfare and defense, passing on toolmaking skills, sharing important past experiences, establishing social bonds between individuals, manipulating potential sexual competitors or mates, caring for and training young, and on and on. [From The Symbolic Species]

In my opinion, the biggest mystery is not why we humans developed language, but why nobody else did. If language is so great, why doesn't everybody have one -- or at least the best approximation they can manage? Judging by their contemporary descendents, the cephalopods of 400 million years ago probably had as many qualitatively different communicative displays as chimpanzees do. Since then, surely, many other species have gotten into situations that motivated symbolic communication for fission-fusion scavenging, or for social group maintenance, or for sexual display, or whatever.

Posted by Mark Liberman at June 11, 2005 09:32 AM