Hand before foot? Cortical somatotopy suggests manual dexterity is primitive and evolved independently of bipedalism.
Hand before foot? Cortical somatotopy suggests manual dexterity is primitive and evolved independently of bipedalism.
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DOI：
10.1098/rstb.2012.0417
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发表时间：
2013-11-19
期刊：
影响因子：
--
通讯作者：
Iriki A
中科院分区：
文献类型：
--
作者：
Hashimoto T;Ueno K;Ogawa A;Asamizuya T;Suzuki C;Cheng K;Tanaka M;Taoka M;Iwamura Y;Suwa G;Iriki A
长期以来，人们一直在猜测，是早期人类的两足行走进化触发了工具的使用（通过解放双手），还是制造和使用工具的必要性促使他们转向直立行走。不管怎样，人们普遍认为是一个导致了另一个。在这项研究中，我们试图通过绘制人类和猴子的手指和脚趾大脑中的神经表征来揭示手巧和两足动物的起源。与上述“手拉手”的概念相反，我们的研究结果表明，潜在的工具使用适应的进化独立于人类两足行走所需的适应。在人类和猴子中，我们发现每个手指在初级感觉运动皮层中是分开的，就像它们在手部是分开的一样。这反映了独立使用每个数字的能力，因为需要在工具使用中进行复杂的操作。然而，受试者脚趾的神经映射却有所不同。在猴子中，脚趾的体位表征是融合的，表明手指在一般抓取中主要作为一个单位发挥作用。相比之下，人类对大脚趾（拇趾）有独立的神经表征，这表明它与两足运动有关。这些观察结果表明，手的大脑回路已经超越了简单的抓取，而我们的灵长类祖先仍然是一般的树栖四足动物。这种早期的适应为手巧的进化奠定了基础，而手巧在古人类中得到了保存和增强。在古人类中，一种单独的适应，包括大脚趾的神经分离，显然是在两足行走时发生的。这与已知的化石证据一致，包括最近报道的440万年前的人类化石。
People have long speculated whether the evolution of bipedalism in early hominins triggered tool use (by freeing their hands) or whether the necessity of making and using tools encouraged the shift to upright gait. Either way, it is commonly thought that one led to the other. In this study, we sought to shed new light on the origins of manual dexterity and bipedalism by mapping the neural representations in the brain of the fingers and toes of living people and monkeys. Contrary to the ‘hand-in-glove’ notion outlined above, our results suggest that adaptations underlying tool use evolved independently of those required for human bipedality. In both humans and monkeys, we found that each finger was represented separately in the primary sensorimotor cortex just as they are physically separated in the hand. This reflects the ability to use each digit independently, as required for the complex manipulation involved in tool use. The neural mapping of the subjects’ toes differed, however. In the monkeys, the somatotopic representation of the toes was fused, showing that the digits function predominantly as a unit in general grasping. Humans, by contrast, had an independent neurological representation of the big toe (hallux), suggesting association with bipedal locomotion. These observations suggest that the brain circuits for the hand had advanced beyond simple grasping, whereas our primate ancestors were still general arboreal quadrupeds. This early adaptation laid the foundation for the evolution of manual dexterity, which was preserved and enhanced in hominins. In hominins, a separate adaptation, involving the neural separation of the big toe, apparently occurred with bipedality. This accords with the known fossil evidence, including the recently reported hominin fossils which have been dated to 4.4 million years ago.
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影响因子：
2.4
作者：
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通讯作者：
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影响因子：
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作者：
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影响因子：
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作者：
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影响因子：
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作者：
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DOI：
10.1098/rstb.2012.0413
发表时间：
2013-11-19
影响因子：
6.3
作者：
Gumert, Michael D.;Malaivijitnond, Suchinda
通讯作者：
Malaivijitnond, Suchinda