The earliest modern-human-like hand bone in the fossil record, which appears different to those from all australopiths and the Homo habilis group, is reported online in Nature Communications. The discovery suggests that a hominin (human ancestor), with a hand more similar to modern humans than any others, co-existed with other ancient hominins called Paranthropus boisei and H. habilis at Olduvai Gorge, Tanzania, more than 1.84 million-years-ago.
Modern human-like (MHL) hands are commonly interpreted as adaptations for the use of stone tools. However, as the hominin fossil record expands, a complex pattern of hand evolution is becoming apparent, with the hand bones of some ancient lineages more similar to modern hands than those of more recent ones. In addition, although the fossil record indicates that the more recent hominins from the Pliocene possessed MHL-hand proportions, most skeletal evidence also indicates that they possessed adaptations for spending considerable time dwelling in trees.
Now, Manuel Dominguez-Rodrigo and colleagues analyse a newly discovered hand bone, which they report is likely part of the little finger of the left hand of an ancient but modern looking hominin lineage (yet unidentified, although similar to Homo erectus) . Using archeological evidence along with their analysis they suggest that just under 2 million years ago this East African hominin lineage showed marked reduction in adaptations for living in trees, along with the expression of an overall modern human-like (MHL) finger bone shape (as far as it is possible to infer from a single bone).
The bone, OH 86, adds to previous evidence indicating that several key aspects of modern human body shape emerged very early in human evolution. However, due to the complex and non-linear nature of skeletal evolution in hominins, further analysis of remains from other regions of the hand (and other anatomical regions) is necessary to clarify key palaeobiological aspects of this hominin species.