The following post was originally presented as a paper at the March 1991 Northwest Anthropological Conference in Missoula, Montana. Unlike most of the other posts I have published, this paper (actually a twenty minute oral presentation) was for an audience of college students, professors, and other professional academics and interested public. Because of that I have received a comment that the train of argument by which I came to my conclusions was difficult to follow in places, confusing, and lacking in detail, as I jumped over things. I apologize for that and can explain it as the result of being written for a specific audience, rather than the general public. Also it had to fit within the time span allotted. Further more there may be some confusion about the title. I have come to realize that “age” may be interpreted as the geological time that the fossil was alive (which is not known with any certainty) rather than how old the child was when it died (which is what I meant).



By Patrick Light

I spend much time outdoors, not as much time as I would like to spend, and maybe not as much time as some people think I do, but still, more time than most people do. On several occasions I have looked at the equipment I carry with me, what little I sometimes need to live comfortably enough in the woods, and I have thought how little it is that we actually need. How simple it can be to satisfy our basic needs. I have also realized how bound we are to these things, how necessary these things and the knowledge of their manufacture and use are for human survival. This is the difference between us and the other living organisms on this earth.

Several years ago, I listened one day, as an excited gradu­ate student told nearly everyone who would listen about an article he had read. The article explained that recent studies had shown the Taung skull to be that of a three year old child, not that of a six year old child as it is usually considered to be. The original estimate that it was six years old is based on the dental development of the skull compared to standard human development rates. The study mentioned in the article had determined, by microscopic examination of its teeth, that the Taung child was three years of age at the time of its death. It is possible to determine the actual time required for various teeth to form and grow by counting lines formed in the teeth (the perikymata). The article’s conclusion was that the Taung child (and by inference all of the australopithecines) had physically developed, matured, at a much faster rate than do modern humans. The rate of development was, in fact, identical to that of the apes.

The graduate student was quite excited and, it seem to me, disturbed, about the “pongid pattern” of growth and development exhibited by the Taung skull. I have never been quite sure what the graduate student had found so exciting or disturbing. He may have feared that, because of this pongid pattern of growth, the australopithecines would be removed from the evolutionary line leading to Homo sapiens, like poor old Ramapithecus. The idea being that if they developed like pongids, then they must be pongids and not hominids.

I did not find the information particularly exciting, or disturbing. The australopithecines did not have a large brain, so why should they be expected to have an extended, a slower, more human, pattern of growth and development? That the bipedal Taung child was only three years old, but developmentally equal to a human child at six years, further demonstrates the mosaic nature of evolution. It was only later, primarily while writing my thesis, that the full implication of this pongid pattern of growth became apparent to me.

The old concept of the Great Chain of Being still affects how we reconstruct evolutionary scenarios, how we visualize evolution. The concept is based on the obsolete idea that each organism, living and extinct, occupies a point along a single line leading from the most primitive to the most advanced, just like links in a chain. Progression from one species to another is gradual and even, where large gaps exist between living species, the “missing links” are species that are now extinct. In a sense, the metaphor is an accurate description. Each living individual, each of the species can trace an unbroken chain of ancestors back across billions of years to a primordial organism that was the first living organism.

The problem with this concept of a chain develops when a gap needs to be filled in. What did that missing link look like? If the gap is small and there is only one link missing, one inter­mediate step, the missing organism is reconstructed with charac­teristics halfway between the two known species. If the gap is a large one and there is more than one link, the reconstructed species show a shift from primitive to advanced characters proportional to the species position between the two known species. If the reconstructed species is 1/4th of the way from the primitive to the advanced species, its traits are 3/4ths primitive and 1/4th advanced. If it is half way, it is one half primitive and one half advanced. A species 7/8ths of the way toward the advanced species, is 7/8ths advanced and 1/8th primi­tive. This does not mean that 7/8ths of the traits are advanced, but that each trait is 7/8ths of the way toward the advanced state. You can see the results of this, using apes and humans as an example, in the older reconstructions of Neanderthal Man. Since he lies somewhere between the apes and modern man, he is an amalgam of characters both ape and human. In more recent ver­sions, he is placed still closer to being human, but still not quite so. He is slightly stooped, intellectually dull, and not fully capable of articulate speech. The australopithecines, are even closer to the apes and therefore were originally thought of as being almost apes. It has taken much evidence and even more argument to change this view. According to the Great Chain of Being Concept, they should have been only slightly bipedal, slightly tool-using, slightly large brained, slightly hairless and slightly articulate. But they are not, and now, we have gone to almost the opposite extreme. Some recent reconstructions make them into hairy, little humans, culturally and linguistically primitive to be sure, but, nonetheless, very human.

The Great Chain of Being was based on the concept of unili­neal evolution. The apes were not modern species that had evolved from some distant common ancestor with man, but they were that ancestor from which man evolved. They had not changed, had not evolved further, only man had. It was even a fashion for a time to place the various cultures and races of man along the chain, in positions ranging from just slightly above the apes, through various grades of primitive to civilized. Even though the unilineal concept of evolution has been replaced by a multi­lineal “tree of life” concept, the Great Chain of Being concept still affects many of our ideas about evolution.

Earlier I mentioned that, lately, we have gone almost to the opposite extreme in our reconstructions of the lifestyles of the australopithecines. The reconstructions make them are very human, more human, I believe, than the evidence warrants.

Apparently, all the australopithecines matured at a rate equal to the apes. This reduces the amount time available for the brain to grow and for the individual to learn. On the face of it, any reconstruction of australopithecine life that is much different from the apes, that postulates much dependence on tools, on an extended and dependent childhood is probably inac­curate. An australopithecine child was what we would call “extremely precocious.” This is not to say that they were exactly like apes. They were doing something different. They were using their brains in a way that the apes weren’t. Neurolo­gical changes were taking place in the brain, it was being reorganized. This reorganization would eventually make it possible for at least one population of australopithecines to become something else.

What I find most interesting is that there is evidence that Homo habilis had the same rate of development as the australopi­thecines. At first glance, that does not seem sensible. Homo habilis was larger brained than the australopithecines and used tools, even made tools. It would seem therefore, that they should have been developing at a slower rate than the australopi­thecines, much slower, more like Homo sapiens. Yet, I will venture to argue, it is reasonable, even to be expected.

Sherwood Washburn has said: “Changes in behavior occurs before changes in morphology.” The changes in the pelvis, the knee, and in the position of the foramen magnum did not occur to allow the hominid to walk bipedally. The changes occurred because of the bipedal behavior of the hominid. In Homo habilis, the behavior was changing, they were using tools more often, they were becoming dependent on tools, on culture (or symboling, if you prefer) for their survival. They were making behavioral changes, changes permitted by their present morphology. The changes created selective pressure for morphologic changes that improved the organism’s capacity for the new behavior. These morphologic changes allowed for further behavioral changes, which led to further morphologic adaptation, a self-reinforcing cycle. Homo habilis had embarked on a new adaptive trend, one different from the australopithecines, and one that had tremendous poten­tial. Each little shift toward greater ability to symbol gave such immense advantage over other populations that the selective pressure for those adaptations was great. Homo habilis didn’t have a chance. Homo habilis barely shows up in the fossil record before being replaced by descendent, Homo erectus, the culture-bearing animal.

The australopithecines lived like pongids, they were a little more intelligent, a little more capable of problem-solving than the apes. Homo habilis had begun to make changes in their behavior, they were tool-users and tool-makers. They were becoming dependent on culture, on the ability to symbol. The morphologic changes that distinguish man from ape were beginning to appear. However, it is with Homo erectus that the morphologic changes occur with full force. Homo sapiens is just the final polishing to these morphologic changes.

I am not surprised that the australopithecines and Homo habilis matured as rapidly as do the apes. They were only beginning to make those behavioral changes that would lead to Homo sapiens. The changes in morphology related to the extended childhood that is the hallmark of cultural man, would occur afterward, in Homo erectus.


Beynon, A. D., and B. A. Wood

1987 Patterns and Rates of Enamel Growth in the Molar Teeth of Early Hominids. Nature 326:493-496.

Bromage, Timothy G.

1987 The Biological and Chronological Maturation of Early Hominids. Journal of Human Evolution 16:257-272.

Bromage, Timothy G., and M. Christopher Dean

1985 Re-evaluation of the Age at Death of Immature Fossil Hominids. Nature 317:525-527.

Brower, Bruce

1987 Hominid Headway. Science News 132:408-409.

Conroy, Glenn C., and Michael W. Vannier

1987 Dental Development of the Taung Skull from Computerized Tomography. Nature 329:625-627.

Smith, B. Holly

1986 Dental Development in Australopithecus and Early Homo. Nature 323:327-330.

Tobias, P. V.

1974 The Taung Skull Revisited. Natural History 83(10)38- 43.