| 1. All the dramas of human evolution took place in Africa |
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KOBAYASHI: When I visited major university medical schools to study the education system worldwide in the beginning of the 70's, I witnessed that universities in Europe and the United States were already moving toward unifying academic fields that were differentiated as physiology, anatomy, biochemistry and the like, and toward studying humans under the rubric of the human sciences encompassing all knowledge from the humanities and social sciences. Wishing to establish a similar concept in research related to children in Japan, I have, since the 70's, been consistently advocating the importance of a multidisciplinary "Child Science." I have a feeling that your field of research, anthropology, and mine share something in common, for both of us strive to study humans through a comprehensive approach. I'm sure that your insights are relevant to Child Science. BABA: You are quite right in pointing out our common efforts to bring together subdivided academic disciplines. Anthropology can be interpreted as a comprehensive approach to understanding humans in the evolutionary process of organisms. In particular, thanks to the rapid progress achieved in recent years in functional anatomy, molecular genetics and dating methods, among others, we can now consider the question of human evolution with a more comprehensive and empirical approach. KOBAYASHI: I understand that there were as many as 20 human species in the past, including us Homo sapiens. Progress in comparative research must have also contributed to discerning various differences within the species. But would you explain how humans have evolved? BABA: Given that anthropology is a discipline that studies humans from the standpoint of evolution of organisms, Darwin's influence is immense. In fact, Darwin postulated that human evolution consisted of a series of events taking place progressively: for instance, humans would have been already large-brained and using tools when they started walking on two feet. Paleontologists, however, have now refuted Darwin's hypothesis. In 1891, the Dutch anthropologist Eugene Dubois discovered fossils of the Java man. The Java man stood upright like modern humans, but his brain capacity was 900 cc, between that of a chimp and a modern human. That was why the Java man was sensationalized as the greatest discovery of the century that was to be the "missing link" between apes and the genus Homo. Likewise, the Australopithecus, discovered in 1924, stood erect, but his brain capacity of 350 cc, comparable to that of a chimp, led to a dispute over whether it was just a variation of the anthropoid or the ancestor of the genus Homo. Those fossils discoveries, admittedly, did not entail the immediate rejection of Darwin's idea. But eventually, as more fossils of the same kind were discovered in Africa and Asia, fewer scholars supported Darwin's view of human evolution as a single set of progressive processes. The fact is that human species became bipedal, and this phase as an upright chimp, so to speak, lasted nearly 4 million years. It was only afterwards that the brain grew larger as a result of tool manipulation and meat eating. Subsequently, it took another hundreds of thousand years or even one million years for human species to develop language ability. So you see, humans have come to be human-like over a long, long period of time, traversing several stages of evolution. KOBAYASHI: Not only Australopith, but also Homo erectus, or even Homo sapiens originated in Africa. Why? BABA: Strangely enough, all the major events in the history of human evolution took place in Africa. This may be attributed to sheer coincidence, say by 50%. But definitely, the biggest factor lay in human adaptability to climatic fluctuations. Africa has experienced three long cycles of drought, and each one may have given rise to a new genus Homo that was more adaptable to dry climates. Thus Australopith evolved 7 million years ago; Homo erectus, 2 million years ago; and, finally, Homo sapiens, 150,000 years ago. KOBAYASHI: That means evolution did not take place through successive transitions, but sporadically, in a sudden leap, so to speak. BABA: That's right. You may say, each major climatic fluctuation brought a new adaptation. As for bipedalism, the former hypothesis that early human species were forced to stand upright when the climatic change drove them out of forests to open grasslands has been refuted today by the fossil evidence that they already practiced the bipedal gait to some extent when they inhabited forests. One basis for postulating their bipedalism in forests is that fossils of early Australopiths have been discovered together with fossils of animals that inhabited forests. Moreover, early Australopiths are known to have had teeth with a thinner enamel layer. You know, the Australopiths that eventually inhabited grasslands ate tough food such as rootstocks and peas had teeth with a thicker enamel layer than that of a chimp's teeth. This trait has been passed down to us modern humans. The fact that early Australopiths had teeth with a thin enamel layer would indicate that their diet consisted of soft fruits, leaves and the pith of trees. |
