Humans and their ancestral hominids belong to one great family: this is the profound conclusion drawn by Rolex Laureate David Lordkipanidze and his colleagues from their latest – and most spectacular – discovery of a 1.8 million-year-old skull from Dmanisi, Georgia.
The mere suggestion that all fossil humans belong to the same species – instead of up to 14 different species arising over the last 2.3 million years, as has been suggested by various scientists – has unleashed the sort of incendiary academic debate that has invariably coloured questions about human origin and ancestry since Darwin published On the Origin of Species in 1859. Some scholars, reluctant to let go of their “pet” species, have responded acrimoniously to the new interpretation with claims of “exaggeration” and “hyperbole”.
Controversy over his finds is not new to archaeologist Lordkipanidze of the Georgian National Museum, for whom the mediaeval town of Dmanisi, situated on a hilltop at an intersection on the old Silk Road between China and the West, has proven a treasure trove. Since 1991, its dark grey sediments have yielded no fewer than five early skulls to his patient excavations, remnants of the first people of the human lineage to venture out of Africa – and begin to conquer the world.
“This hominid collection is the richest and most complete collection of indisputable, early Homo remains from any site or comparable stratigraphic context in the world,” Lordkipanidze observes. “Up to now, we have unearthed five hominid skulls, four of them with jaws. Their state of preservation is exceptional, enabling us to study many previously unknown aspects of the skeleton of fossil hominids for the first time, and in more than one individual. Thanks to the volcanic origin of the Dmanisi sediments, the site has been confidently dated to 1.77 million years before the present.”
Together with the pre-human bones, an enormous variety of animal and plant remnants have come to light, enabling the scientists to reconstruct the local climate at the time: it was temperate and damp, and the landscape was mantled with dense forest and steppe. Stone tools found at the site and cut marks on animal bones show these ancestral people were active meat eaters and probably good hunters – a notion also suggested by the eagle’s eye view of the surrounding landscape afforded by the hilltop site where they were found.
“Geologic analysis of the stratification pattern of the site suggests that all hominid and faunal material was transported by water over a short distance, then rapidly covered by sediments,” Lordkipanidze explains. “The time frame for the formation of the site is relatively short, which leads to the conclusion that the bones were all deposited at the same time.”
In another astonishing aspect of the find, one of the individuals appears to have lost most of his or her teeth early in life – an event generally fatal to roaming animals – but here suggesting the group had already developed the ability to care for its weaker members.
To assist with further archaeology, the preservation of this remarkable site and the creation of a museum and visitor centre, Lordkipanidze was selected as a Laureate of the Rolex Awards for Enterprise in 2004. The fifth skull, which has prompted all the debate, was found on 5 August 2005 (Lordkipanidze’s birthday, by chance) – but it has taken scholars a further eight years to fully analyse and describe it. Their conclusions, published in the journal Science in October 2013, were what prompted fresh debate over the human lineage and put archaeology on the front pages of many of the world’s newspapers.
“Skull 5 from Dmanisi is an extraordinary find in many respects. It represents the most complete skull of an adult fossil Homo individual found to date,” says Lordkipanidze’s colleague, Dr Marcia Ponce de Leon. “The fossil is perfectly preserved, and free of any deformation or fragmentation which often occur during the process of fossilization. The jawbone was found in 2000; the cranium was found five years later, less than two metres from the mandible.”
Skull 5 has a small braincase with a volume of only 546 cubic centimetres, barely one third that of a modern human. It has a large and protruding face with massive jaws and large teeth, and thick eye brow ridges. This unusual combination of features was not known before from early fossil hominids and provides a significant new glimpse of what an early adult Homo looked like.
From the close proximity of the skulls when found and from their anatomical features, Lordkipanidze and his colleague, Dr Christoph Zollikofer of Zurich University, conclude that the five individuals represent a single group of humans or “deme”. They interpret the notable physical differences between the individual skulls as displaying the sort of variation not uncommon in a group of people – and conclude all are simply variants of a single ancestral species, Homo erectus. Until now many prehistorians have tended to regard H. erectus, Homo habilis, Homo rudolfensis, and other differing hominids found in Africa as distinct species. In their Science article, the Dmanisi team argue that the variation seen in the Georgian skulls is no greater than the variation between these other early human types, and has in any case a strong family resemblance to the African fossils.
“When seen from the Dmanisi perspective, morphological diversity in the African fossil Homo record around 1.8Ma [million years ago] probably reflects variation between demes of a single evolving lineage, which is appropriately named H. erectus. The hypothesis of multiple independent lineages appears less parsimonious, especially in the absence of empirical evidence for adaptation to independent ecological niches,” they wrote in Science. This is the claim that has set the scientific cat among the prehistoric pigeons. In short, it suggests that all humans are descended from a single common species around 2 million years ago – and what were regarded as separate, extinct offshoots of the family tree may just be cousins after all.
Together, the evidence points to an adventurous group of these early people moving eagerly out of Africa around 1.8 million years ago into lands where the climate, vegetation and many of the animals were unfamiliar to those raised on the African savannah. Boldly they thrust north up the Great Rift Valley, along the shores of the Red Sea, then following the game trails, forged across the Middle East and up along the rugged western border of Turkey into the Caucasus Mountains, between the Black and Caspian seas. Here, 5000 weary kilometres later, they finally found a rocky, wooded plateau rising steeply between the swift-flowing Mashavera and Pinezaouri rivers, a perfect lookout situated above a narrow pass where they could observe the migration of elephants, gazelle, rhinos, sabre-toothed cats, giraffes, bears, ostriches, wolves and other mammals. And here, unaccountably, tragedy overwhelmed them.
That discoveries even more startling and profound in terms of how humans see themselves lie ahead, Lordkipanidze does not doubt. “We can say for sure that Dmanisi has enormous potential to yield new discoveries as we know that at least 50,000 square metres of the site contain stone tools – and these still remain to be excavated for fossil humans.”
Julian CribbLearn more about David Lordkipanidze