Some suggest that these muscles are a result of toolmaking. There are three muscles that are unique to the human hand and all of them flex the thumb in different ways, underlying our unique use of our thumb for precision and strength gripping. We also have different musculature in our hands than other primates. By Homo habilis hands were more similar to modern humans, though more robust than modern humans. Her spine suggests that this amount of time was not great because it is very flexible and much better adapted to walking than climbing where she may risk injury. Curved finger bones in Lucy and her species suggest that they spent some time in trees, as well as walking bipedally. Evidence suggests that metacarpals have elongated in apes while they have shortened in humans since our last common ancestor. Longer fingers are associated with grasping tree branches to hang from. Humans use their hands with a combined precision and strength grip that allows us greater dexterity with our hands.Īrdi’s fossils are useful for determining when hands diverged between humans and other apes. Chimpanzees use their fingers to grip sticks while humans use their thumbs to allow for greater control and precision. They have short thumbs and long phalanges compared to our more modest phalanges and large, strong thumbs. Our hand bones are different than those of chimps in very significant ways. Next, Roberts discusses the ability of human and ape wrists to be in both supinated and pronated positions allowing us to use our hands for even more things. Skeletal differences between human and chimpanzee hands show that our hands serve different functions despite their seeming similarity (Roberts 324). There is conclusive evidence that throwing was used for hunting by 300,000 years ago. There is little fossil evidence of throwing before the invention of tools specifically designed as projectile weapons such as throwing spears. This seems to have been very important because much of our anatomy seems well suited for throwing. Some suggest that the change in shoulders may be because of advantages for throwing. Perhaps they conferred an advantage for long distance running. Roberts discusses possible reasons that our shoulders have rotated downwards. Other apes have more upward facing shoulders because of their use for climbing. They have the ability to pronate which allows rotation around the arm-hand axis. Shoulders are a very mobile and as a result of this mobility, they dislocate more easily than more stable joints. We have free-floating scapulae and very mobile arms. Our shoulder anatomy is owed in part to our climbing ancestors. Human arms and hands are much more mobile than those of most other mammals. She also talks about the things we share with other apes as well as what sets us apart and why these differences may have arisen. The findings of the study also challenge the assumption that a chimp-like hand was the starting point of the chimpanzee-human LCA.In this chapter, Roberts addresses the unique physiology of the human shoulder and hands and how they reflect our evolutionary past. These results support the hypothesis that the long thumb to fingers ratio of the human hand was acquired convergently with other highly dexterous anthropoids. Their results show the more recent, convergent evolution of finger elongation in chimpanzees and orangutans and comparatively little change between humans, human ancestors and gorillas. The researchers measured the hand proportions of humans, living and fossil apes as well as fossils of human ancestors including Ardipithecus ramidus and Australopithecus sediba, to understand the step wise evolution of the hand. This is one of the most distinctive traits of humankind compared to apes and is often cited as one of the reasons for the success of the species however there are competing theories on how the human hand evolved over time. Human hands exhibit a long thumb in relation to the fingers. These findings indicate that the structure of the modern human hand is largely primitive in nature, rather than the result of selective pressures in the context of stone tool-making. Human hand proportions have changed little from those of the last common ancestor (LCA) of chimpanzees and humans. The work is done by Stony Brook University's Sergio Almecija, Jeroen Smaers and William Jungers.
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