Favourite ‘ancestor’ is erased from the family tree - again
Australopithecus sediba has been demoted as our relative
Ever since an intriguing set of fossils was found in the Cradle of Humankind in 2008, experts have been at loggerheads about whether they represented our main ancestor or not.
Lee Berger, of the University of the Witwatersrand, found the fossils with his nine-year-old son, and after more in-depth work across a range of disciplines, the species known as Australopithecus sediba made its way into the science books.
Two years after that discovery, Berger claimed A. sediba as the exclusive ancestor of Homo.
Though the brain was smaller than ours and the face not as flat nor the teeth as small, it was the human-like pelvis and ability to walk upright that led to the ancestral theory.
Many in the science fraternity were then convinced that the first of the Homo genus, from which modern-day humans are derived, had been found.
But dissenting voices quickly emerged, as that claim had really shaken up the family tree.
Lucy was up until then in the pound seat. She was the Australopithecus afarensis found in Ethiopia in 1974 and dated to 3.2 million years ago.
For four decades, she was considered the most likely immediate ancestor of our own genus, Homo – right until A. sediba came along.
But now, in yet another round of this paleontological boxing match, scientists from the University of Chicago are demoting A. sediba from her spot on our family tree.
They say their statistical analysis of fossil data shows the odds that A. sediba is our direct ancestor is “close to zero”.
The study was published this week in scientific journal Science Advances, and restores Lucy as our most likely ancestor.
Lead researcher Andrew Du maintains Australopithecus afarensis (Lucy) is a better candidate for the direct ancestor of Homo for a number of reasons.
A. afarensis fossils have been dated up to three million years old, nearing the age of the first Homo jaw.
Lucy and her counterparts, including Selam, the fossil of an A. afarensis child that was discovered in 2000, were found in Ethiopia, just kilometres from where the Homo jaw was discovered.
The jaw’s features also resemble those of A. afarensis closely enough that one could make the case that it was a direct descendant.
“Given the timing, geography and morphology, these three pieces of evidence make us think afarensis is a better candidate than sediba,” say the researchers.
“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.”
This time last year, the University of Michigan ordered a female lifelike reconstruction of what it termed “an extinct human relative” – meaning A. sediba – for a new natural history museum.
Her shining eyes and hairy, upright body, standing just 114cm tall, made for an endearing ancestor, but whether she was truly a human relative was a question that already had palaeontologists scratching their heads since she was found a decade before.
In April last year, around the same time the statue was under construction, a study published in the South African Journal of Science said A. sediba could not be written off as our ancestor, even though some experts had claimed she wasn’t in the running.
This latest paper is likely to not be the last in an ongoing process that intermittently has two different species appear on our family tree as our main ancestor, only to be erased and then pencilled in again.
Shortly after the new study was published, Berger took to Twitter to question and somewhat discredit the new findings, with the #notenoughevidence hashtag accompanying his tweet summing up his view.
“So if I understand, there is a near 0% chance that #sediba is the ancestor of the genus Homo based upon 2 fragmentary surface finds, the older of which can hardly be distinguished from sediba but if those are wrong then the study is wrong?”