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| A picture released on August 18, 2015 by Nature Communications shows a OH 86 hominin manual proximal phalanx in (from L-R) dorsal, lateral, palmar (distal is top for each) and proximal views [Credit: AFP/Rodrigo Dominguez] |
It also hints at the existence of a larger, more human-like creature than others known to have lived at that time in the same region—one of the hotspots of human origin—in modern-day Tanzania.
The hand is one of the critical anatomical features distinguishing humans, and even a 3.6-centimetre (1.5-inch), two-million-year-old fragment can reveal a lot about body type and behaviour.
The shape of our forebears' hands was both a reflection of their stage of evolution, and a driver of that evolution, explained lead author Manuel Dominguez-Rodrigo, a researcher at the Institute of Evolution in Africa in Madrid.
"Our hand evolved to allow us a variety of grips and enough gripping power to allow us the widest range of manipulation observed in any primate," he said by email.
"It is this manipulation capability that interacted with our brains to develop our intelligence, mainly through the invention and use of tools."
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| A picture released on August 18, 2015 by Nature Communications shows an OH 86 hominin phalanx overlaid on a modern human hand [Credit: AFP/Jason Heaton] |
One is a longer thumb, allowing us to grip more precisely and to open our hands more fully.
Another is the straightening of our phalanges, the general name given to the three bones found in each finger. Curved phalanges were adapted for climbing trees and swinging from branches.
"A modern-like hand in the past would tell us when humans became fully terrestrial and when and how efficiently our ancestors used tools," Dominguez-Rodrigo said.
That transition happened in two main stages.
After the earliest hominins—which includes all members of the Homo genus—began walking on two legs some six million years ago, the hand evolved a longer thumb.
But the fingers remained curved, suggesting that trees remained part of their habitat.
This "double locomotion"—on the ground, through the trees—remained the norm for another four million years.
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| A picture released on August 18, 2015 by Nature Communications shows people excavating the fossiliferous layer at PTK in the Olduvai Gorge, one of the most important paleoanthropological sites in the world [Credit: AFP/Rodrigo Dominguez] |
The existence of a bigger, more modern-looking hominin would help explain this puzzle.
Other experts not involved in the study agreed.
"It brings support to those who challenge the view that Homo habilis was the maker of the stone artifacts becoming abundant in layers of this time period," commented Jean-Jacques Hublin, director of the department of human evolution at the Max Planck Institute for Evolutionary Anthropology.
At the same time, Hublin and others challenged the broad conclusions reached on the basis of such slim evidence.
"One single bone from a pinkie finger does not imply a whole modern human-like skeleton," Hublin said by email.
Another leader in the field, Tracy L. Kivell of the School of Anthropology and Conservation at the University of Kent, was even more sceptical.
"This single bone tells us nothing about what the rest of the hand looked like, let alone what the rest of the skeleton looked like," she told AFP by mail.
"If recent, more complete hominin fossil discoveries have taught us anything, it's that strange combinations of more derived human-like features and more primitive australopith-like features throughout the skeleton are likely the rule, rather than the exception, especially at this time period."
The study has been published by the journal Nature Communications.
Author: Marlowe Hood | Source: AFP [August 18, 2015]
