Have you ever wondered why each of the five fingers of the hand has its own name – index, heart, ring … – and, on the other hand, we do not have the same consideration for the feet? In a way, it is a side effect of standing, the ability to move with an upright posture that differentiates us from the vast majority of quadruped mammals. Because, distant and less appreciated than those of the hands, the fingers of our lower extremities lost their grasping ability, to grasp objects, typical of primates, over the course of evolution. This anatomical innovation drastically changed the configuration of the human body and triggered the social and cultural development of our species.
Now, a team of international scientists in which Peter Fernández, from the University of Stony Brook, in the United States, and Sergio Almécija, from the Catalan Institute of Paleontology Miquel Crusafont, in Sabadell, has participated, has investigated how the ossicles were transformed, soft tissues and joints of those little five undervalued appendages that top off our feet.
Using 3D scanners, experts have compared the structure of the joints between the metatarsal and phalanges – called metatarsophalangeals – of different species of primates: from the fossils of our hominid ancestors, to great apes – gorillas, chimpanzees, bonobos and orangutans. -, other monkeys and, of course, modern Homo sapiens .
Published in the scientific journal PNAS , the study indicates that Ardipithecus ramidus – the oldest known hominin that stood up – already has adaptations that allow upright posture, about 4.4 million years ago. Specifically, researchers have found that their metatarsophalangeal joints are oriented upward to facilitate movement on two legs. This trait differentiates A. ramidus from other primates, which have these joints oriented downwards to prioritize the grasp of objects.
The big toe, a case apart
The work also makes another revelation: that the characteristic big toe of the human foot evolved much later , when the first species of the genus Homo appeared , to give a greater boost to the steps or strides of a race. In an interview with the BBC, Peter Fernández explained that perhaps it is because it was more difficult to transform and, also, because the ancient hominins continued to spend a lot of time in the trees and continued to use their feet to pick up things, before completely abandoning their arboreal habits.
This adds a new piece to the scientific puzzle of human standing, although the origin of this ability remains an enigma . Perhaps it was caused by a climate change that wiped out much of the wooded area of the African savanna or, simply, our ancestors freed their hands to make and handle tools.
What is clear is that modern bipedalism appeared in a late period and that it was the result of gradual adaptations, separately. Some experts suggest that, at least from the time of Ardipithecus ramidus , hominins experimented with different forms of vertical displacement until that of Homo sapiens was established.
More information: Fernández, PJ, Mongle, CS, Leakey, L., Proctor, DJ, Orr, CM, Patel, BA ., Almécija, S., Tocheri, MW, Jungers, WL (2018, published online). “Evolution and function of the hominin forefoot”. PNAS (2018) https://doi.org/10.1073/pnas.1800818115
