Our results suggest that the similarities among the hands of living apes are only apparent. Our findings could surprise many: After many morphometric analyses and phylogenetically-informed comparisons, my colleagues and I found that the hand proportions of early hominins (e.g., Ardipithecus, ~4.4 Ma) are not substantially different from some fossil apes pre-dating the ape-human split (e.g., Ekembo, ~18 Ma Pierolapithecus, ~12 Ma). To understand the roots of the human hand and check if the human hand originated from a chimpanzee-like hand, we needed to compare the hand anatomy of early hominins with that of fossil apes pre-dating the times of the LCA. Over the years, I joined forces with colleagues from all over the world to have a new look at old fossils. Subsequently, the story goes that handy skills and bigger brains (associated with enhanced cognition ever more sophisticated technology) went hand-by-hand. Hence, a popular notion in human evolution is that our fingers became shorter and our thumbs longer to manipulate objects better and make stone tools. However, modern apes are better suited to move in the tree canopy. Chimpanzees (like the other living apes) can’t do it because their fingers are too long relative to their thumbs. However, living apes are more limited in their “precision grips.” Now imagine yourself throwing darts. Apes use forceful “power grips” habitually, humans too (e.g., visualize yourself using a hammer). The primate hand anatomy reflects a compromise between locomotion and manipulation. Even more, primates benefit from prehensile hands (i.e., one-hand grasping), whereas most other mammals need both hands to hold objects (imagine a squirrel chewing on a nut). For example, was the LCA a knuckle walker like chimpanzees and gorillas? Was it “suspensory,” hanging below the tree branches? Hints about the locomotion of chimpanzee-human LCA can be found in the hand of living and extinct species. Why the hand? Current debates relating to the chimpanzee-human LCA’s hand morphology are fueled by competing inferences regarding this ancestor’s locomotor repertoire. The salary was small and the working hours long, but hey, after years of internships and work as a technician, I would become a professional researcher! I was given a unique opportunity, and I wasn’t going to miss it.ĭid other aspects of the human body evolve from a chimp-like ancestor? I decided to check this idea for the case of the hand. On the other hand, my now colleagues David Alba and Salvador Moyà-Solà (my future advisor), who directed the work in Els Hostalets, invited me to study the hands of Pierolapithecus and Hispanopithecus (see cover image). That year I got lucky: On the one hand, I received a pre-doctoral fellowship from the Catalan government, allowing me to focus on research starting the following year. No doubt, the most famous fossil from the area (and likely the entire country) is the partial skeleton of the ~12 million-year-old fossil great ape Pierolapithecus. I spent 10+ hours a day working as a field paleontologist in Els Hostalets de Pierola (near Barcelona), which is well known for its amazing paleontological discoveries. At the time, I had just graduated from college. The greater mobility of the human thumb, and our enhanced ability to manipulate small objects with thumb tip-to-finger tip precision grips, likely evolved for finer manipulative abilities in the context of increased dependence on, and elaboration of, technology.I have been researching the origins of this “uniquely” human structure since 2005. These differences, especially with respect to relative thumb length, make it difficult for non-human primates to employ tip-to-tip precision grips when manipulating small objects (such that small objects must generally be pressed by the thumb against the lateral side of the index finger). However, humans differ from other primates in having a relatively longer and more distally placed thumb (see Relative Thumb Length) and in having larger thumb muscles (the thumb muscles constitute about 39% of the mass of the intrinsic hand muscles in humans, as compared to only 24% in chimpanzees). Humans share pollical opposability with most other catarrhines (old world monkeys and apes). This ability is facilitated by a sellar (saddle-shaped) joint between the trapezium (the wrist bone that supports the thumb) and the first metacarpal, which allows an approximately 45° range of rotation of the thumb about its own long axis. Humans have an opposable thumb, meaning that they are able to simultaneously flex, abduct and medially rotate the thumb (pollex) so as to bring its tip into opposition with the tips of any of the other digits.
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