Charybdis

Why don’t chimpanzees or at least some other primates talk?

This question is one of the central puzzles for anybody trying to give an evolutionary account of speech origins. Until it is answered properly, those people who favor Samuel Johnson’s explanation that speech was provided through divine inspiration (see: Johnson’s Table Talk) cannot be easily refuted.

The question was posed by three Swedish scholars, Sverker Johansson, Jordan Zlatev, and Peter Gärdenfors as an objection to an article by John Locke and Barry Bogin. The Swedes felt the article did not clarify why meaningless song rather than speech was insufficient, or why meaningful speech, if it was required, appears nowhere else in the biological world.

Locke and Bogin offered a reply, part of which was analyzed in yesterday’s post (here). Today I want to take a look at the part of the answer that tried to address the question of meaningful speech. They write that the human line evolved what they call “cooperative breeding” as a means of increasing the survival rate of their offspring and that speech was a “means to reduce social conflict and foster cooperation.” (p. 304)

Elsewhere in their discussion Locke and Bogin explain what they mean by “cooperative breeding”:

Perhaps the most important attribute leading to reproductive success is human cooperative breeding. By this we mean the cooperative childcare and feeding by nonmaternal kin and non-kin that is essential to ensure the survival of a weaned child. Cooperative breeding has evolved independently in several species of mammals, birds, and insects. In those species, and in many but not all human groups, the helpers are close genetic relatives of the mother. By assisting the mother to care for her offspring, the helpers increase their own inclusive fitness, meaning that they increase the chances that their genetic kin will survive to reproductive age. Unlike other species, human societies define kinship relations on the basis of social as well as genetic ties. In traditional human societies, kinship is the central organizing principle for economic production, social organization, and ideology. Human cooperative breeding, therefore, enhances the social, economic, political, religious, and cultural “fitness” of the group as much or more than it contributes to genetic fitness. (p. 303)

This is interesting and very important because it points out a striking difference between humans and all other species. Traditional human communities may seem like animal societies that are organized around kinship, but kinship in human communities does not require a genetic relationship.

A common way for people outside the genetic line to become kin is through adoption. A child is in need because its parents are dead. (Possibly, back in Homo habilis times, because the mother was dead, the father being unknown.) Somebody takes it in and raises it as their own. That child is not just raised as their own; the duties and taboos of kinship apply. The child, for example, cannot eventually marry a “brother” or “sister” despite the absence of a genetic connection.

This inattention to genetic ties is contrary to the heart of modern evolutionary thought, which is based on the proposition that at its heart evolution is a competition between genes.

To allow for such a situation without rejecting Darwin requires two things:

1. The basis of community behavior cannot be genetic (because if it were, selfish genes would eventually triumph); and
2. The result of the community behavior has to be so triumphant that selfish genes never find an opening to override whatever is causing the community behavior.

For the past week and more I have been making posts that report on a nonverbal, communication system that creates emotional ties. (See: Infant Babbling; The Persistent Burden; Scylla and Charybdis) These emotional ties are made particularly strong through vocalizations between mother and child.

Now let us fast forward through time so that some cooperative breeding has developed. That is to say, with the rise of the childhood period (see yesterday’s post, here) with its heavily dependent, weaned children, a form of genetically supported, cooperative breeding of the type described by Locke and Bogin has emerged. It looks like a plausible development, and since it happens in many animal societies posses no huge conundrums. Indeed, some such cooperation is observed today among the great apes. The difference here is that through vocalization emotional bonds beyond the genetic pressures are being created, so that if Mama habilis dies through some misadventure the surviving Weaned habilis is a problem. Among chimpanzees (and presumably Australopithecus) the death of a mother of a dependent infant spells doom for the infant, but here we have other females with an emotional attachment to the survivor. Adoption, as an emotional rather than a genetic action, becomes a possibility.

You might expect a genetic distaste for adoption to arise eventually in these circumstances, and probably it would have if the solution hadn’t proved so amazingly successful. Locke and Bogin offer the following statistics:

human reproductive success … is greater than that of any other mammal. The social mammals, such as wolves, lions, and elephants, rear about 12–18% of their live-born offspring to adulthood. Our closest living relative, the chimpanzee, rears about 36% of its live-born offspring to maturity. But human hunter-gatherers and horticulturists, living in traditional societies without the benefits of modern medical care, rear about 60% of their infants to adulthood. Industrial societies of North America and Western Europe successfully rear at least 95% of live-born infants to maturity .(p 303)

The kind of success seen by hunter-gatherers is so far superior to anything seen in the rest of the animal world that, instead of resisting it, evolutionary pressures are going to promote it, transforming us from one more genetically-competitive species into a cooperative-community species. Presumably H. habilis did not do as well as modern Bushmen, but even a slight improvement in overall survival would have been decisive.

Increased survival based on emotion was a revolutionary change, something akin to finding a way to breathe on dry land. It opened a seemingly infinite variety of niches to us. But what, you ask, remembering the subject of this blog, has all this got to do with speech?

Nothing, I’m afraid … at least nothing directly. Locke and Bogin are amazingly cavalier about the why-don’t-chimps-talk question. They concede, “Cooperative breeding has evolved independently in several species of mammals, birds, and insects,” so why don’t at least some of these other cooperative breeders talk if, as Locke and Bogin assert, language arose to assist cooperative breeding?

I don’t see this path leading to speech. Something may turn up, of course. Locke and Bogin have done a splendid job in getting us to notice the implications of inserting a childhood stage between infancy and juvenile independence. And, along with the input from their peers, this clarifies the pressures for developing emotional vocalizations. (And I haven’t yet even gotten to their important work on the adolescent stage.) But I am skeptical that this way leads toward talk (meaningful speech). Their work suggests a way to goo-goo our way past Scylla (the problem of emotional communication), but as for talking our way beyond Charybdis … well, we still need a good map.

Comments

[Gordon Worley]

Two points.

First, you say "The basis of community behavior cannot be genetic", which, is of course, nonsense. All behavior is "genetic" insofar as any physical or psychological or social trait or behavior is tied to human genetics. To deny genetic influence anywhere is to deny Darwin. Rather, perhaps you mean it arose as information passed between generations?

Further on the issue of genetic influence, although modern behavior is clear, the explanation given doesn't show an evolutionary path to "community breeding". How did these animals go from "individualists" to "communalists"?

One possibility follows. Humans (and some other animals) live in groups. To consider just humans, they live in social groups of kin, even if there are several generations of removal between the extrema of the group. Even with members entering and leaving, the group remains fairly close genetically, and caring for the young of deceased group members leads to the propagation of "adoption genes". But the "adoption genes" have a broad effect and humans become willing to adopt any human child, even out of group, and as a side effect we get "community breeding" for the entire human community.

I'll leave the remainder of the explanation for now; I have to go to work.

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BLOGGER: Most people, including most Darwinians, believe that there is some behavior that is not genetic. Amongst humans the idea is usually not controversial because so much behavior is cultural. There is probably not a genetic distinction between, say, those who favor the war in Iraq and those who do not. Amongst animals it is less obvious, but even there we have local habits, the Manyara tree climbing lions are a famous example as are the different tools used by different chimpanzee groups. There is also a great deal of "imprinted" behavior, as in the famous case of goslings following Konrad Lorenz. Identical twins have identical genes but they do not have identical personalities or identical behaviors.

[TLTB]

I agree with the blogger, but would just add the addendum that many culturally learned behaviors may still have a basis in genetics, just an indirect one. Chimps learn to use to different tools (cultural), but they are all able to use them (genetic).

Also, reading students of identical twins who have been separated at birth is fascinating. One in fact finds that such twins often develop very similar personalities and even behaviors (choosing highly similar occupations and spouses, for example). Its a bit scary to think such things might have such a strong genetic basis.
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BLOGGER: Thanks for the support. While I take your point about a basis in genetics, the question is really where the explanatory power lies. A great deal of behavior can be explained in cultural, conditioned, emotional, intellectual, or imprinted terms. The genetic basis is so general that it adds nothing to the explanation, not even in selective terms. Similarly, the chemical bonds making the structure of a gene possible rests on quantum laws, but those laws offer no explanatory assistance when discussing, say, emotional behavior.

There is a lot to be said about identical twins, and they do enable some statements about what percent of many things are genetic. It is only when confronted by an over the top claim like all behavior is genetic that I would appeal to their differences.

[Gordon Worley]

I put my point rather tersely and sharply, but you can find a gentler explanation of this position here: http://www.psych.ucsb.edu/research/cep/