In my previous post I discussed the similarity between chimpanzees amd bonobos, who our closest living relatives, and how different they seem to be in comparison to us, despite a relatively recent (6 million year old) split from our Last Common Ancestor (LCA).
While preparing that post I came across an old paper written by Tocheri, Orr, Jacofsky, and Marzke in 2008 (The evolutionary history of the hominin hand since the last common ancestor of Pan and Homo. J Anat. 2008 Apr;212(4):544-62. doi: 10.1111/j.1469-7580.2008.00865.x. PMID: 18380869; PMCID: PMC2409097). That paper compares the morphology of the hands of Pan, humans, and our older Homo ancestors (Neanderthals, H. erectus), as well as those of other hominins (H. floresiensis and Autralopiths).
The paper is interesting, and the authors reached some revealing conclusions about hand shape and the possible effects of the development of Acheulean stone tool usage and the shape of human (and Homo) hands.
The authors found a clear division in the hand-shapes of pre-Acheulean and Acheulean hominins. On one side are Australopiths, Paranthropus, other early Homo, and the Homo floresiensis, who share primitive features with the LCA. On the other, are the Neanderthals, Homo erectus, Homo antecessor, and modern humans, whose hands developed "Derived changes" over the past 2.5 million years (Ma) and probably even later (1.5 Ma). These dates coincide with the dates when Acheulean stone knapping technology developed.
This suggests, to Tocheri et al., that the shape of the modern human hand evolved to adapt to stone manipulation.
The authors wonder if "the complete suite of derived characteristics present in the hands of modern humans and Neandertals originated earlier with H. erectus sensu lato or possibly with another closely related hominin species" and affirm that "the evidence reviewed in this paper suggests that currently only three species of the genus Homo (H. sapiens, H. neanderthalensis, and H. antecessor) display derived hand morphology that is noticeably absent elsewhere in the hominin lineage, including H. floresiensis... this evidence suggests that these features... may have originated sometime between approximately 1.8 and 0.8 Ma, a temporal span that encompasses the origin and initial spread of Acheulian technology (∼1.5–0.2 Ma). This does not imply that the derived features of the radial wrist are necessary to make or use Acheulian tools, only that the current evidence suggests that these features probably originated within a temporal and behavioral context characterized by Acheulian technology."
Despite their cautious comments, there seems to be a distinct line separating Australopiths and Paranthropus, and even the minute Homo floresiensis of Indonesia, from later, more developed Homo humans like Homo erectus, H. antecessor, Neanderthals, and us. I am positive that when Denisovan hands are discovered, they too will be part of this second group.
Primitive, older / earlier hominins, which are not Homo, don't share the Homo shape hand with us.
The H. floresiensis, which is a Homo, has been included in the "primitive" group. The Flores Island Hobbit has been considered by some authors (see Argue, 2017) to be "a long-surviving relict of an early (>1.75 Ma) hominin lineage and a hitherto unknown migration out of Africa, and not a recent derivative of either H. erectus or H. sapiens" Others, like Kaifu, 2015, based on dental morphology, disagree, and suggest it evolved from early Javanese H. erectus, possibly a case of insular dwarfism.
There is something distinctly unique in human hands, they have allowed us to shape the environment we live in, fashion our tools, clothes, homes, touch, write, create artistic objects. They have evolved in parallel with our brains. Other smart, bright animals (think, orcas, or dolphins) lack the physical attributes necessary to manipulate the world around them. Elephants use their trunks to interact on subtle and manipulative ways with their surroundings, but it is far less delicate than human hands.
This paper seems to find a link between human cognition and hand shape, and the development of Acheulean tools, more sophisticated than the previous cobble type stone tools of the Oldowan stone industry. Later, Neanderthals evolved their Mousterian tools, and humans would advance with other more efficient knapping techniques. But the crucial point was the creation of Acheulean tools, 2 Ma, by the erectus.
Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia Copyright 2009-2026 by Austin Whittall ©
Hello Austin. You are treating a fascinating topic…
ReplyDeleteIndeed, it does make sense that the “Rubicon” (or point of no return) at which the hominid hand began to acquire the characteristics and functionalities seen in modern humans could chronologically be placed at the emergence of the first Acheulean tools…
Even considering that H. erectus technology may not have relied entirely on the manufacture of sophisticated bifacial tools (in fact, not all their sites contain them), since it would be reasonable to speculate that such technology flourished not only to provide higher efficiency at hunting, but also as a response to more complex hierarchical structures of the human groups and/or increased exchange of goods with neighbors (aspects that ultimately could have been related with the local demography)… in any case, what does seem clear is that the hands of H. erectus should have already possessed (perhaps as early as 1.6 million years ago) some advanced biomechanical features in order to complement his “opposable thumb” (a trait already present in their predecessors) with more mobile carpal-metacarpal joints, that in turn led to the ability to rotate their metacarpal bones radially (i.e., towards the thumb), and also with a better proportioned size in their digits (basically; a larger thumb, and shorter 2nd and 5th digits), among other improvements... being the conjunction of them responsible of the ability of the hand to perform what is known as a “precision grip”.
It is well known that the hands of all previous species within the ape-human phylum (LCA (Last Common Ancestor) included) although being rudimentary, were already capable of a “power grip”, as they could form some sort of “hook” with their digits… However, the above mentioned “precision grip” is an additional capability that granted H. erectus (and also other Homo) a skill that revolutionized the manufacturing process of their implements and tools… The underlying question would be; What about its correlation with an improved cognition...?. As a tentative answer to it, I would propose another one; …What if we consider that the gradual increase of dexterity in their hands for performing specific tasks (increasingly unrelated to locomotion) could have constituted, by itself, the major catalyst towards the stimulation of certain areas of their brains related to cognition… ?
Amazing post.
Best regards.
Marcelo
Thanks for the comment Marcelo.
DeleteYour suggestion that precise grip and dextrity may have been a catalyst for an enhanced cognition is thought provoking. Erectus, their advanced tool production capability in comparison to previous Homo, and their dispersal across the Old World suggest that they were intelligent creatures. In my opinion, probably the "real" first Homo (relegating the Oldowan and cobble type tool hominins to a previous, less brainier group, with Australopiths and Paranthropus).
I too believe that H. erectus could have literally dominated the scene of genus Homo evolution… and yes, you may probably be right considering it as the “real” first Homo…
Delete