Shields E D
Department of Oral Biology, Faculty of Dentistry, McGill University, Montreal, Quebec, Canada.
J Craniofac Genet Dev Biol. 2000 Jan-Mar;20(1):1-9.
In the assessment of human origins, chimpanzees (Pan troglodytes, henceforth called Pan) represent the best hominoid outgroup for comparisons. Such an outgroup roots the "anatomically modern" human population cluster, or continuum. This study incorporates chimpanzees into a worldwide modern human database of quantified complete tooth variables (approximately 30 per tooth; e.g., root, pulp, enamel) in an attempt to develop a more accurate phylogeny of the hominoid continuum, with only intervening extinct hominids missing. Canonical discriminate analysis was performed mainly among Liberian common chimpanzees and global samples of humans. The first canonical variable explained 70% of the total variance and showed a tight cluster of humans, with chimpanzees as a distant outgroup. Within the human community, first non-San Bushman, sub-Saharan Africans and Andamanese, and then, close in, Australian aborigines were positioned towards Pan. Their relative orientation suggested an African human origin with the first branch within sub-Saharan Africa: sub-Saharan Africans and San Bushmen. Next, Andamanese Negritos, and then Australian aborigines, formed the early first surviving modern human lineage to leave Africa. Thin enamel and big teeth with relatively large roots characterized Pan nonmolar teeth. Humans showed a generalized sexual dimorphism for all teeth, with males having bigger teeth, bigger relative roots, and thinner enamel than females, while only Pan canines had significant and impressive sexual dimorphism. Interestingly, Pan molars were not larger than human molars. The data suggest that although hominids underwent two dental macroevolutionary events, the lineage leading to modern humans only experienced anterior tooth-size reduction. The suggested evolutionary significance of the observed total tooth variation is discussed.
在人类起源的评估中，黑猩猩（黑猩猩属，以下简称“黑猩猩”）是进行比较的最佳类人猿外群。这样一个外群为“解剖学上现代的”人类种群聚类或连续统奠定了基础。本研究将黑猩猩纳入一个全球现代人类数据库，该数据库包含量化的完整牙齿变量（每颗牙齿约30个变量，例如牙根、牙髓、牙釉质），试图构建一个更准确的类人猿连续统系统发育树，中间仅缺少已灭绝的原始人类。主要在利比里亚普通黑猩猩和全球人类样本之间进行了典型判别分析。第一个典型变量解释了总方差的70%，显示人类紧密聚类，黑猩猩作为远外群。在人类群体中，首先是布须曼人以外的其他人、撒哈拉以南非洲人和安达曼人，然后是澳大利亚原住民，逐渐靠近黑猩猩。它们的相对位置表明人类起源于非洲，第一个分支在撒哈拉以南非洲：撒哈拉以南非洲人和桑人布须曼人。接下来，安达曼尼格利陀人，然后是澳大利亚原住民，形成了最早离开非洲的现代人类幸存谱系。黑猩猩的非臼齿具有薄牙釉质和相对较大牙根的大牙齿特征。人类所有牙齿都表现出普遍的性别二态性，男性牙齿比女性更大、相对牙根更大、牙釉质更薄，而只有黑猩猩的犬齿具有显著且明显的性别二态性。有趣的是，黑猩猩的臼齿并不比人类的臼齿大。数据表明，尽管原始人类经历了两次牙齿宏观进化事件，但导致现代人类的谱系只经历了前牙尺寸减小。本文讨论了所观察到的牙齿总体变异的进化意义。
