Fifteen years ago, in the field of human origins studies, we thought we had it all figured out. The story of human evolution, while “bushy,” was relatively straightforward. Sometime around 5 million years ago, a small-brained bipedal ape arose from a split with the lineage that would give rise to chimpanzees and bonobos — perhaps in the form of the genus Ardipithecus. This lineage likely arose in east Africa, or further north in the Ethiopian highlands. What followed, based on convention and the science of the times, was an almost predictable march of progress through time. Australopithecines would arise around 4 million years ago, likely in eastern Africa as well, in the form of species like anamensis and the famous Lucy’s kind afaransis. Some diversification would take place after 3 million years ago with the first appearance of “gracile” hominids in southern Africa in the form of the species Australopithecus africanus. So-called “robust” australopiths would at the same time emerge in east Africa, but both the former species and latter lineage would be considered dead ends, little more than distractions on the main trackway of human origins.
By 2.5 million years ago it was thought the genus Homo arose, again in east Africa, though no fossils had been found to support this age, it being largely based upon the idea that climate change around that time had driven the origins of our genus. From this early Homo arose primitive members of the genus, like Homo habilis and rudolfensis, both thought to be associated with the earliest stone tool industry, the Oldowan. In this turn-of-the-century story, one of these species, most likely habilis, gave rise to Homo erectus in Africa before 1.8 million years ago and the story of our origins was almost over. Erectus would give rise to an archaic Homo sapiens sometime in the late Middle Pleistocene around 500,000 years ago and we would emerge as an African species about 150,000 years ago, colonizing the whole of the old world by 60,000 years ago and the Americas around 12,000 to 15,000 years ago. A few side-branches like Neanderthals in Europe along the way made this not a line, but a tree or bush. The story of our evolution as an African species was largely spelled out, so much so that one of the leading paleoanthropologists in the field at the turn of the 21st century proclaimed that there would be no new discoveries to alter this picture, that the fossil record held no new surprises and that fossil hominins were perhaps the rarest sought after objects on Earth — and discoveries were in decline. So much so that we should stop training young scientists to be paleoanthropologists! To be fair, in hindsight, this was probably not an unusual opinion, but one held by many, if not most in the field.
But the discoveries of the last decade or so have proven that this simple story line of human origins, and the predictions of this scientist were (fortunately) wrong. Discovery after discovery has shaken the foundations of the linear and simplistic model of human origins. From tiny, small-brained hominins on the island of Flores, first suggesting that humans had shared the planet with another species as recently as the last several tens of thousands of years, to breakthroughs in genetics and ancient DNA that continue to challenge almost every premise of the genetic sanctity of species, to the discoveries I have had the privilege of being involved in down in southern Africa — Australopithecus sediba and Homo naledi. Each of these discoveries, and too many others to mention here, are transforming our very understanding of human origins. It is clear now that our story is wonderfully complex, and it’s wonderfully messy at the same time. There was no “march of progression.” Small-brained hominins like the hobbits and naledi existed and thrived into the same time periods as modern humans were evolving. To place the pace of discovery into perspective, more fossils hominins have been found in the past three years in Africa than in the previous 80 years combined, and most of them from just a couple of sites, like the Dinaledi and Lesedi Chambers outside of Johannesburg! These new species, new technologies and new ways of looking at evolution are setting the stage for a revolution in understanding the complexity of the pathways of how we came to be. It is furthermore clear from these discoveries that we should move away from trying to find a single source for the “evolutionary hotspot” of human origins in any one region of Africa — ours is not simply an “East Side Story.” Many events in many diverse regions of the continent, and perhaps beyond, were involved in the rise of our species. It is also manifest that the old idea of ladder, tree or even bush is too simplistic a model and perhaps the human evolutionary journey should be likened to a braided stream feeding a vast delta, the rivulets of the stream being these extinct fossil human relatives and the lake or ocean at the end being the more than 7 billion living humans. With the slaughtering of the old sacred cows of our field, and the pace of discovery paralleled by the pace of technology, the next few decades promise to truly be the greatest age in understanding humanity’s origins out of Africa.
Paleoanthropologist Lee Berger is an Explorer in Residence with the National Geographic Society and author of Almost Human: The Astonishing Tale of Homo naledi. He also serves as research professor in human origins and the public understanding of science at the University of the Witwatersrand in Johannesburg, South Africa.