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Mesial-distal and buccal-lingual crown measurements were made on male and female samples of recent Japanese teeth from three locations, Fukuoka, Kyoto, and Tokyo, and for Hokkaido Ainu and Koreans. Similar data were collected for prehistoric Middle-to-Late Jomon Japanese and from Yayoi specimens representing the first agriculturalists to appear in Japan. From a tooth-by-tooth comparison of cross-sectional areas, it was shown that the modern Japanese samples did not differ from one part of Japan to another. Korean tooth size also is not significantly different from Japanese, while Ainu have the smallest teeth recorded in Asia. The Yayoi who brought rice to Japan about 300 B.C. came in with teeth that were the same size as Chinese Neolithic teeth. They encountered a resident Jomon population whose teeth were 10% smaller. From tooth size measures alone, it is most economical to suggest that, if the rates of reduction observed elsewhere in the world applied in Japan, the recent Ainu would best be regarded as the direct descendants of the Jomon, while the modern Japanese are the results of in situ reduction from the incoming Yayoi. Other aspects of craniofacial morphology suggest that some Jomon was incorporated by the Yayoi. The modern Japanese, then, while predominantly derived from the Yayoi, would include a Jomon component.

Human craniofacial data were used to assess the similarities and differences between recent and prehistoric Old World samples, and between these samples and a similar representation of samples from the New World. The data were analyzed by the neighbor-joining clustering procedure, assisted by bootstrapping and by canonical discriminant analysis score plots. The first entrants to the Western Hemisphere of maybe 15,000 years ago gave rise to the continuing native inhabitants south of the U.S.-Canadian border. These show no close association with any known mainland Asian population. Instead they show ties to the Ainu of Hokkaido and their Jomon predecessors in prehistoric Japan and to the Polynesians of remote Oceania. All of these also have ties to the Pleistocene and recent inhabitants of Europe and may represent an extension from a Late Pleistocene continuum of people across the northern fringe of the Old World. With roots in both the northwest and the northeast, these people can be described as Eurasian. The route of entry to the New World was at the northwestern edge. In contrast, the Inuit (Eskimo), the Aleut, and the Na-Dene speakers who had penetrated as far as the American Southwest within the last 1,000 years show more similarities to the mainland populations of East Asia. Although both the earlier and later arrivals in the New World show a mixture of traits characteristic of the northern edge of Old World occupation and the Chinese core of mainland Asia, the proportion of the latter is greater for the more recent entrants.New World origins ͉ craniometrics ͉ prehistoric population relationships

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Published evidence indicates sharp reductions in the hominid dentition following the end of the Pleistocene. These reductions, both in size and in morphological complexity, have proceeded farthest in those areas where culture change has occurred most rapidly. The model proposed here suggests that post-Pleistocene dental reduction may be the result of the change in selective forces consequent from the invention and use of pottery and the changes in foodpreparation techniques after the end of the Pleistocene. Models for testing this hypothesis are discussed.''. , . if it is undeniable that since the Paleolithic dental evolution has occurred in the sense that there has been a diminution in the number of teeth, a reduction in their volume, a simplification i n their form and a n approximation of their roots, it is no less doubtful that the occurrence of mutations at times has come to complicate and influence the general manner of that evolution." (translated from Brabant and Twiesselmann, '64:55, original in italics).

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Starting with the onset of the last glaciation approximately 100,000 years ago and continuing to the end of the Late Pleistocene approximately 10,000 years ago, human tooth size began to reduce at a rate of 1% every 2,000 years. Both the mesial-distal and the buccal-lingual dimensions of mandibular and maxillary teeth were undergoing the same rate of reduction. From the beginning of the Post-Pleistocene until the present, the overall rate of dental reduction doubled, becoming approximately 1% per thousand years. Buccal-lingual dimensions are now reducing twice as fast as mesial-distal dimensions, and maxillary teeth are reducing at an even more rapid rate than mandibular teeth. Late Pleistocene rates are comparable in Europe and the Middle East. The Post-Pleistocene rates are also the same for Europe, the Middle East, China, Japan, and Southeast Asia. It is suggested that the cookery at the beginning of the Late Pleistocene allowed the earlier changes to occur. The use of pottery within the last 10,000 years further reduced the amount of selection that had previously maintained usable tooth substance. Reduction then occurred as a consequence of the Probable Mutation Effect (Brace, 1963; McKee, 1984).