Ape-like fossil discovered in South Africa and thought to represent a human ancestor is NOT in our direct lineage after all, study finds
- New study focuses on called Australopithecus sediba found near Johannesburg
- It has human-like pelvis, face, and teeth, so many thought it was Homo ancestor
- It would push timeline of direct human descendants forward by 800,000 years
- A new analysis has ruled out this scenario almost entirely, putting debate to end
- Team concluded that famous ‘Lucy’ fossil is still the most likely direct ancestor
A fossil thought to be the direct ancestor to the Homo genus has been all but ruled out by scientists who say the statistical probability of a match is ‘close to zero.’
The analysis, published this week in Science Advances by paleontologists from the University of Chicago, focuses in on a fossil called Australopithecus sediba, which was discovered inside a cave near Johannesburg eight years ago.
Because of its physical characteristics, which include a human-like pelvis, face, and teeth, researchers proposed that A. sediba was the direct ancestor of Homo erectus, the first of the Homo genus from which modern day humans are derived.
A new study says it has ruled out a link between the fossil Australopithecus sediba and humans. Fossil casts of Australopithecus afarensis (left), Homo habilis (center), and Australopithecus sediba (right)
HOW DOES A. SEDIBA FIT INTO HISTORY?
The first A. Sediba fossil was found in 2008 in a cave outside of Johannesburg.
The specimen was encased in stone — researchers posit that millions of years ago, a mother and her child fell into a fissure where they were washed by a rainstorm into a pool and immortalized into the rock.
A skeleton of A. sediba share striking similarities to humans including similar teeth, faces, and bone structure.
The problem, says a new study, is that it would postdate previous understanding of human relatives by 800,000 years.
As a result, the experts say it is highly unlikely that the specimen can rightfully displace other ancestors which date back as far as 3 million years.
The assertions were significant for their implications on the timetable of the human genus, particularly the fact that A. sediba would push the previously understood timeline of direct human descendants forward by 800,000 years.
‘What is remarkable about Australopithecus sediba is that, as a field, it is a discovery we never thought would be made: a bona fide transitional species,’ Lee Berger, a palaeoanthropologist at the University of Witwatersrand in Johannesburg told The Guardian following the release of the study in 2011.
It’s because of that dramatic shift in timeline that researchers say A. sediba is most likely not our direct relative.
‘It is definitely possible for an ancestor’s fossil to postdate a descendant’s by a large amount of time,’ said the study’s lead author Andrew Du, PhD.
‘We thought we would take it one step further to ask how likely it is to happen, and our models show that the probability is next to zero.’
The researchers note that the link is not altogether impossible — in the past, discoveries have reset the chronology of humans by sizable margins.
In 2017, a fossil discovery In Africa revealed that modern humans roamed the Earth about 100,000 years earlier than previously thought.
This, note researchers, is still drastically lower than the 800,000 years projected by A. sediba.
‘We see that it’s possible for an ancestor’s fossil to postdate its descendant’s,’ Du said.
‘But 800,000 years is quite a long time.’
Previous discoveries have upended the understanding of when humans roamed the Earth, setting it back 100,000 years. An illustration of human evolution is shown
In place of A. sediba, researchers say that Australopithecus afarensisis, known from the famous ‘Lucy’ fossil discovered in 1974, is still the most likely direct ancestor to humans.
The Lucy fossils as they’re known, are dated about 3 million years ago.
‘Given the timing, geography and morphology, these three pieces of evidence make us think afarensisis a better candidate than sediba,’ said Zeray Alemseged, PhD, the Donald M. Pritzker Professor of Organismal and Biology and Anatomy at UChicago.
‘One can disagree about morphology and the different features of a fossil, but the level of confidence we can put in the mathematical and statistical analyses of the chronological data in this paper makes our argument a very strong one.’
WHEN DID HUMAN ANCESTORS FIRST EMERGE?
The timeline of human evolution can be traced back millions of years. Experts estimate that the family tree goes as such:
55 million years ago – First primitive primates evolve
15 million years ago – Hominidae (great apes) evolve from the ancestors of the gibbon
7 million years ago – First gorillas evolve. Later, chimp and human lineages diverge
A recreation of a Neanderthal man is pictured
5.5 million years ago – Ardipithecus, early ‘proto-human’ shares traits with chimps and gorillas
4 million years ago – Ape like early humans, the Australopithecines appeared. They had brains no larger than a chimpanzee’s but other more human like features
3.9-2.9 million years ago – Australoipithecus afarensis lived in Africa.
2.7 million years ago – Paranthropus, lived in woods and had massive jaws for chewing
2.6 million years ago – Hand axes become the first major technological innovation
2.3 million years ago – Homo habilis first thought to have appeared in Africa
1.85 million years ago – First ‘modern’ hand emerges
1.8 million years ago – Homo ergaster begins to appear in fossil record
800,000 years ago – Early humans control fire and create hearths. Brain size increases rapidly
400,000 years ago – Neanderthals first begin to appear and spread across Europe and Asia
300,000 to 200,000 years ago – Homo sapiens – modern humans – appear in Africa
50,000 to 40,000 years ago – Modern humans reach Europe
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