Science Matters – unravelling our deep origins

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Early human evolution is shrouded in mystery. We know that our early ancestors split from chimpanzees, our closest ape relative, around 7-8 million years ago (Myr), and that the first near-humans of our genus (Homo) evolved in Africa at least 2.5 Myr.

These forerunners eventually gave rise to us (Homo sapiens), but our knowledge of what happened between these dates is very limited, largely because fossilised remains are extremely rare.

Common illustrations depicting how our upright posture, facial features and lack of body hair gradually evolved are based on few skeletons of ancient ancestors. Most notable is that of Lucy, a young female skeleton dating back to 3.2 Myr.

Lucy was discovered in the Afar depression, Ethiopia, in 1974, and was assigned to a species more primitive than ours (Australopithecus), and named A. afarensis after her location. In the 1990s a few teeth and bone fragments were found that proved to be similar to, but even older than, Lucy, dating from ^4 Myr and called A. anamensis. it was assumed that Lucy was directly descended from this ancient primate.

Not surprisingly, there was much excitement in the field when anthropologist Yohannes Haile-Selassie discovered a near-complete skull of A. anamensis dating from approximately 3.8 Myr. He found the skull, simply known as MRD for now, during his fieldworks at Woranso-Mille, Ethiopia, in 2016. As the oldest and most-complete skull of A. anamensis, this find allowed detailed comparison with Lucy’s species.

There was general agreement that, like the illustration, our ancient ancestors descended one from another in a linear fashion. So most experts assumed that A. anamensis evolved directly into Lucy’s species.

Haile-Selassie’s detailed study of MRD suggests, however, that the two species co-existed in Africa for at least 100,000 years, presumably with the potential for interbreeding. This undoubtedly shakes up previous thoughts and reshapes our understanding of Homo evolution.

But only time will tell; Haile-Salassie says he hopes to find the rest of MRD’s skeleton – and even earlier members of our Homo genus – which should certainly help unravel our deep past.

*Nature 573, p214. 2019. Nature 576, p368. 2019.