New human ancestor discovered (Science) – Experts respond

AusSMC: A team of scientists, including three Australians, have uncovered the skeletal remains of a new species of ancient human. The researchers suggest the species – named Australopithecus sediba – could be a direct ancestor to Homo erectus, the predecessor of modern humans.

skullThe two partial articulated skeletons of an adult female and child were found in miners’ debris in South Africa in the Cradle of Humankind World Heritage Site in 2008 by Professor Lee Berger from South Africa’s University of the Witwatersrand.

Australian scientists Dr Andy Herries from the University of New South Wales, Dr Robyn Pickering from the University of Melbourne and Dr Paul Dirks from James Cook University were part of an international team that identified and dated the fossil as being around 1.95 million years old. This places the new species at a transition point in our evolutionary story from small brained bipedal apes to larger brained human ancestors. Two papers describing the discovery and dating procedures will be published in the journal Science.

Comments from the scientists involved in the research:

Dr Andy Herries is an archaeological scientist from the School of Medical Sciences at the University of New South Wales. Andy was part of the team who dated the remains and is an author on the paper.

“Until recently it was impossible to get precise dates for the South African cave sites, but with the development of new techniques we are beginning to understand the relationships of the various species of early human to each other. This is a period of major climatic change and increasing aridity in Africa, when a number of different species of potential early Homo ancestors occur, each adapting to these changes in different ways. Sediba appears to have traits of both the earlier species, Australopithecus africanus, and a later species, Homo erectus.

“It is likely that these fossils do not represent the oldest evidence for Au. sediba. Sediments older than 2 million years occur at the site and only time will tell if they will reveal earlier examples of Australopithecus sediba or other species of human ancestors.”

Professor Paul Dirks is Head of the School of Environmental Sciences at James Cook University. He lead the team which described the geological setting and age of the remains.

“Dating involved a double blind U-Pb date, conducted independently by Jan Kramers of the University of Bern in Switzerland and by Dr Pickering of the University of Melbourne, which is a first in the dating of flowstone deposits in the Cradle of Humankind. Once an absolute date had been obtained, paleomagnetic analysis by Dr Herries of the University of New South Wales was used to constrain the age of the debris flow encasing the fossils. These ages coincide with the period in which the species of the genus Australopithecus are gradually being replaced by species of the genus Homo, of which we, Homo sapiens are part.”

Dr Robyn Pickering is from the School of Earth Sciences, University of Melbourne. She was part of the team who dated the remains and is an author on the paper.

“It has never been clear where our own genus Homo came from – this new discovery, Australopithecus Sediba could answer these questions. Knowing how old these early human (hominin) fossils are, is critical to our knowledge of where this newly found species fits into our family tree. The dating techniques used by myself, Professor Jon Woodhead at the University of Melbourne and my former supervisor Professor Jan Kramers from the University of Bern in Switzerland produced the same dating results of 2 million years old. Together with palaeomagnetic dating of the sediments surrounding the fossils by Andy Herries of UNSW and our team of colleagues lead by Professor Paul Dirks from the University of Townsville, we have been able date the Sediba fossils to between 1.95 and 1.78 million years ago. This is the first time in South Africa, we have been able to achieve such good age control. Now we are able to fill in the gap of what happened 2 million years ago in the beginnings of our species.”

Comments from experts not involved in the research:

Dr Darren Curnoe is a specialist in human evolution from the School of Biological, Earth & Environmental Sciences University of New South Wales Sydney. He has worked extensively in South Africa on the fossil human collection.

“The discovery of one, let alone two, partial skeletons of the fossil relatives of humans is a rare and truly amazing thing. Added to this, is the remarkably young geological age of these new finds. They are substantially younger than any known member of this primitive human-like group, the australopithecines. It also adds yet another branch to our evolutionary tree and confirms an emerging picture of nature’s grand experiment with human-like apes, living humans the sole survivor of evolutionary tinkering. These remarkable facts would usually be enough to secure researchers a place in the history of science. Unfortunately, they seem not to have been enough in this instance, as the discovery is surrounded by hype and over-interpretation, in terms of its significance. To claim that these new fossils represent an ancestor of living humans is misleading and founded in error. Australopithecus sediba is the wrong species, in the wrong place, and at the wrong time. It is way too primitive to be the ancestor of the human genus Homo, one of our direct ancestors. For a start, fossil Homo is known from East Africa to be almost half a million years older. The skull, tooth, and limb bone anatomy of the older Homo also looks very different from those of sediba. Finally, a number of key skulls compared to the new sediba remains have been incorrectly described leading to false conclusions about its place in human evolution.”

Professor Maciej Henneberg is the Wood Jones Professor of Anthropological and Comparative Anatomy at the University of Adelaide

“The new find is important. Skeletal and dental remains are relatively well preserved and provide large amount of information about the individuals studied. Their characteristics fit well into their time period. They are a mixture of Australopithecus and human characters indicating a transitional form to Homo. Finding of such form is entirely expectable for this time period and the location in Southern Africa. I am not sure, however, whether a designation of a new separate species is necessary. In the human lineage there is a natural range of variation of charactersitics of individuals and the new finds fit into this range. One of the features used by the Authors as indicating a new species is the relatively small cranial capacity 420 ml. Hominid cranial capacity is highly variable, it does not correlate with intelligence and thus some individuals within the same species may have smaller, others larger cranial capacity. No need to use it as a trait separating species. Similar comments apply to other characteristics of the new find. In conclusion: an important find having transitional characteristics between Australopithecus and Homo, but not necessarily a new species.”

Professor Colin Groves is from the School of Archaeology & Anthropology at the Australian National University

“We must congratulate the team on a magnificent discovery, while disputing their assessment of its taxonomic affinities. The new ‘australopithecine’ is actually a new species of Homo. Judging by the description, it is a South African sister species to the contemporary east African Homo habilis.

“In fact, the authors themselves pointed to certain similarities with early Homo, seeming even to admit that the predominance of its features were with Homo, only the small cranial capacity being really an “australopithecine” feature. But we now know of Homo floresiensis with the cranial capacity more or less the same as the new species.

“Many of the other features they mention which led them to conclude this fossil is Australopithecus are not strong distinctive features and are present in other species of Homo.

“The whole idea of the genus Australopithecus is actually very vague. All too many palaeoanthropologists use it as a place to stick any fossil of the human clade that is not Homo (at the “upper end”) or one of the very early ones like Ardipithecus or Orrorin. It is what has been called a wastebasket category, whereas if it is to have any value it should be used for a clade within the human clade (a lineage of its own, that is to say): so far, we know only of Australopithecus africanus (a South African species that is somewhat earlier than the new species) that fits this requirement as far as Australopithecus is concerned: all the others generally included in the genus belong to separate lines of descent.”