Nature:人类牙齿在逐渐退化
Nature中文摘要 · 2016/03/02
根据一项新的研究,人类的智齿在人类进化的过程中逐渐在缩小,可能的原因是人类对工具的使用使得尖利的牙齿变得不那么必要。该研究还可以帮助人们理解不同的人类化石、类人化石之间的亲缘关系。相关研究发表在《Nature》上。


根据一项新的研究,人类的智齿在人类进化的过程中逐渐在缩小,可能的原因是人类对工具的使用使得尖利的牙齿变得不那么必要。该研究还可以帮助人们理解不同的人类化石、类人化石之间的亲缘关系。相关研究发表在《Nature》上。


Figure 1: All hominins show the inhibitory cascade pattern for dp3–dp4–m1 triplet, but species of Homo show greater reduction in size of posterior molars.

尽管现代人类是人类族谱唯一的幸存者,其他物种曾经也在地球上生活过。由于人类祖先或者类人猿的化石都非常有限,这使得确定不同类人猿物种间的亲缘关系还存在着很大困难。牙齿是最经常被发现的古人类化石,因为它们是人体中坚硬的部分。该研究作者之一、澳大利亚墨尔本莫纳什大学的进化生物学家Alistair Evans认为,在古人类考古中,牙齿化石的地位很高。牙齿不仅能够提供关于该生物的物种信息,还可以了解该物种的食性、儿童期的发育时间等等。


Figure 2: Prediction surfaces for hominin tooth sizes based on inhibitory cascade and scaling of inhibitory cascade reversal with m1 size.

研究人员说古人类的牙齿已在整个进化过程中逐渐变小。最显而易见的是位于口腔后部的智齿,其尺寸变化非常明显。在现代人类中,智齿往往非常小或甚至不会发育出来,而在许多其它类人猿、智人中则尺寸很大,其咀嚼表面比现代人类的智齿要大二至四倍。


Figure 3: Hominin prediction plot for primary postcanine rows.

以前的研究表明,在现代人类智齿大小这种缩小趋势是由于烹饪或饮食中的其他变化导致的。然而,本文作者们认为,这种转变可能在人类进化更早的阶段就出现了。研究者们的推测是,在某个时候,早期智人开始使用更先进的工具。使用工具意味着人类祖先并不需要那么大的牙齿和下巴。这可能使得人类先祖会花费更少的资源来发育牙齿,使牙齿逐渐变小。


Figure 4: Phylogenetic distribution of tooth sizes and proportions in hominins shows an origin of the Homo pattern shortly after the origin of the genus.

这些牙齿的模式,可以帮助研究人员确定类人猿或者古人类化石是否属的智人或者与人类有怎样的亲缘关系。未来的研究,可能会揭示出新的智人物种。

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  • A simple rule governs the evolution and development of hominin tooth size

    The variation in molar tooth size in humans and our closest relatives (hominins) has strongly influenced our view of human evolution. The reduction in overall size and disproportionate decrease in third molar size have been noted for over a century, and have been attributed to reduced selection for large dentitions owing to changes in diet or the acquisition of cooking1, 2. The systematic pattern of size variation along the tooth row has been described as a ‘morphogenetic gradient’ in mammal, and more specifically hominin, teeth since Butler3 and Dahlberg4. However, the underlying controls of tooth size have not been well understood, with hypotheses ranging from morphogenetic fields3 to the clone theory5. In this study we address the following question: are there rules that govern how hominin tooth size evolves? Here we propose that the inhibitory cascade, an activator–inhibitor mechanism that affects relative tooth size in mammals6, produces the default pattern of tooth sizes for all lower primary postcanine teeth (deciduous premolars and permanent molars) in hominins. This configuration is also equivalent to a morphogenetic gradient, finally pointing to a mechanism that can generate this gradient. The pattern of tooth size remains constant with absolute size in australopiths (including Ardipithecus, Australopithecus and Paranthropus). However, in species of Homo, including modern humans, there is a tight link between tooth proportions and absolute size such that a single developmental parameter can explain both the relative and absolute sizes of primary postcanine teeth. On the basis of the relationship of inhibitory cascade patterning with size, we can use the size at one tooth position to predict the sizes of the remaining four primary postcanine teeth in the row for hominins. Our study provides a development-based expectation to examine the evolution of the unique proportions of human teeth.

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