Exploring the existence of better hands for manipulation than the human hand based on hand proportions. (7th March 2018)

• Record Type: Journal Article
• Authors: Hu, Di; Xiong, Cai-Hua; Liu, Ming-Jin
• Is Part Of: Journal of theoretical biology. Volume 440(2018)
• Page Start: 100
• Page End: 111
• Publication Date: 2018-03-07
• Subjects: Manipulative ability -- Hand morphology -- Kinematic model -- Functional explanation -- Robotics; Biology -- Periodicals; Biological Science Disciplines -- Periodicals; Biology -- Periodicals; Biologie -- Périodiques; Theoretische biologie; Biology; Periodicals; 571.05
• DOI: 10.1016/j.jtbi.2017.12.026
• Languages: English
• ISSNs: 0022-5193

Abstract

Highlights: More possible hand proportions except that of extant anthropoids are reconstructed. Based on hand proportions, we use a kinematic model to assess manipulative ability. Results reveal too long and too short thumbs are both adverse to manual dexterity. Theoretically, better hands for dexterous manipulation than human hand are found. The hand proportions of human may be a trade-off between multiple functions. Abstract: Human exhibits the most dexterous manual manipulation among the anthropoids. The sophisticated dexterity of human hand has been linked to its distinctive morphology compared to the nonhuman anthropoids. The human hand is derived from the ancestral hands after longtime evolution. However, there are more possible morphologies that the hands could take during the evolutionary process. It remains unknown whether better hands for manipulation than the human hand exist among these possible hands. To answer the question, the relationship between the manipulative capability and hand morphology need to be investigated in the region of more possible hands. Here we employ a kinematic model to quantitatively assess the manipulative ability of the possible hands from the aspect of hand proportions. The segment length proportions of each possible hand are reconstructed by the major evolutionary patterns of the anthropoid hands. Our results reveal that too long and too short thumbs relative to fingers both hamper the manual dexterity, though the long thumb of human hand is traditionally thought to be beneficial to manipulation. The results promote the understanding of the link between hand morphology and function. Furthermore, we find out the optimal hand for dexterous manipulation within the region reconstructed by the major evolutionary patterns of the anthropoid hands. The optimal hand is more dexterous than the human hand. Compared to the optimal hand, the human hand has shorter metacarpals relative to phalanges, which is thought to be advantageous to the prehensility. It suggests that the human hand is not an organ exclusive for the dexterous manipulation, but a trade-off between multiple functions.