User:Fama Clamosa/Hand/Evolution
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Phylogenetic studies suggest that a primitive autonomization of the first CMC joint occurred in dinosaurs some 365 million years ago; that a real differentiation appeared approximately 70 million years ago in early primates; and that the shape of the human thumb CMC finally appears about 5 million years ago. This evolutionary process has resulted in the human CMC joint being positioned at 80° of pronation, 40° of abduction, and 50° of flexion in relation to an axis passing through the 2nd and 3rd CMC joints. [6]
- Below are my attempts to describe the evolution of the human hand. A disordered WIP. Fama Clamosa (talk)
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When appendages acquire some form of articulation and muscular autonomous control or become integrated under the control of a central neurological system and permit specific adaptive behaviors coordinated with vision or other sources of relevant information, they are called limbs. Although there are still some gaps in the fossil record, the palaeontology of fishes and early tetrapods allows us to trace back the evolutionary transition from fish to air-breathing, four-legged land vertebrates some 370 millions years ago, when fins evolved into limbs. The evolution of the primate hand, with its characteristic power and precision grips, has been the object of intense scrutiny both neuro-anatomic and functional. Tree-dwelling primates feeding on insects, leaves, fruits and nuts while keeping their balance on limbs or hanging from branches, in addition to grooming, courting, fighting and nurturing, had their hands full, so to speak. Arboreal ecology implies a range of constraints which have molded the early physical and cognitive abilities of primates. Many of these evolved competencies have been conserved in most monkeys and apes, sometimes as the very basis of their existence, sometimes simply making possible alternative ways of life for moving, resting, or hunting. In humans, environmental circumstances can rather easily revive vestigial capacities that enable survival strategies exploiting the resources of trees for escaping danger and providing nutrition. A hardwired grip-reflex is well documented in human neonates and even in the absence of any visible support an adult who trips or loses his/her balance tends to spontaneously produce a grasping gesture. |
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— Bouissac 2004, Gestures in Evolutionary Perspective[1] |
“ | The skeleton of the human hand has its evolutionary origin in the anterior fin of primitive fishes following a reduction process. Starting with 20 to 30 elements, the number of bones reduces to eight. This does not follow a continuous pattern but is influenced by environmental factors. This becomes particularly evident when considering the development of the opposition of the thumb. The muscles of the hand evolve from dorsal and palmar compact plates which are divided into two layers. The differentiation process follows the development of the fingers. The development of the individual hand is controlled by a group of homeobox genes. Comparable genes are found in many different species. The more recent evolution of the hand can be understood as the expression of the development of the brain. Therefore, the hand is a direct tool of our consciousness. It is a main source of differentiated tactile sensations as well as a precise working organ. Gestures, finally, are direct expressions of our personality. | ” |
— Evolution of the hand, Putz & Tuppek 1999 |
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The fossil record indicates that adaptation for throwing and clubbing began to influence hand structure at or very near the origin of the hominid lineage and continued for millions of years thereafter. During this prolonged period of evolution, the hand underwent a profound remodelling that increasingly adapted it for grasping spheroids in a manner that allows precise control of release and for gripping clubhandles with strength sufficient to withstand a violent impact. Two unique human handgrips were thereby produced. Called the ‘power’ and ‘precision’ grips by Napier (1956) who identified and described them, they can also be referred to as clubbing and throwing grips on the basis of their evolutionary origins.
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— Young 2003[2] |
“ | Symbolic behaviour among humans and non-human primates incorporates the hands, and in human ancestors opportunities to use the hand for this purpose must have increased with the evolution of habitual bipedal posture and locomotion. In tracing the evolution of human symbolic behaviour it is therefore important to trace the origins of human bipedality, and to explore the progressive changes in hominid hand structure and functions that may have affected the use of the hands in communication.
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— Evolution of the hand and bipedality, Marzke[3] |
“ | By about 2.6 million years ago, some hominins were making and using simple stone artifacts in eastern Africa. [...] Because the earliest stone artifacts were of such simple construction and because chimpanzees, orangutans, and capuchin monkeys today can employ stones, stems, vines, and sticks to extract nutritious morsels from protective covers, one need not expect that early hominin toolmakers displayed modern hand structure and exquisite motor control.
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— Human Evolution, Encyclopædia Britannica[4] |
“ | [...] a majority of primitive features most likely present in the Pan-Homo last common ancestor are retained in the hands of Australopithecus, Paranthropus/early Homo, and Homo floresiensis. This evidence suggests that further derived changes to the hands of other hominins such as modern humans and Neandertals did not evolve until after 2.5 Ma and possibly even later than 1.5 Ma, which is currently the earliest evidence of Acheulian technology. The derived hands of modern humans and Neandertals may indicate a morphological commitment to tool-related manipulative behaviors beyond that observed in other hominins, including those (e.g. H. floresiensis) which may be descended from earlier tool-making species. | ” |
— The evolutionary history of the hominin hand since the last common ancestor of Pan and Homo., Tocheri et al. 2008[5] |