The Human Origin story has just gotten a bit more complicated. If it wasn’t already complicated enough.
Over the last ten years or so, paleontologists and experts in human origins have proposed that a bipedal species that lived in Africa, and whose fossils were excavated in South Africa was actually an ancient ancestor of humans.
Timing and Human Origins
But a new study, published in the journal Science Advances contradicts the theory maintained for more than 10 years arguing that the ‘scenario is highly unlikely. Researchers have found that the fossils of the Australopithecus sediba are up to 800,000 years younger than the oldest Homo specimen.
The authors of the new study argue that the result strengthens the idea that the now-extinct hominin A. afarensis is probably the true ancestor of humans and not australopithecus sediba as it has been maintained until now.
A. Afranesis, our ancient ancestor
“I had no doubt in my mind—nor did many in our field—that A. sediba could not have been the ancestor of Homo, not only because the earliest known representative of Homo is 800,000 years older, but also because A. sediba does not have all of the morphological features that one would expect to see from the earliest Homo,” explained Yohannes Haile-Selassie, a physical anthropologist from the Cleveland Museum of Natural History in an email to Gizmodo.
As noted by the researchers, an excavated jawbone of the oldest Homo fossil was found to closely resemble that of an A. afarensis jaw. The oldest Homo fossil, the jawbone of a still-to-be-identified species of early humans can be traced back to around 2.8 million years ago, and that means it’s up to 800,000 before the arrival of A. sediba.
Theory in theory
The idea that humans descended from the A. Sediba species can be traced back to the analysis of 2-million-year-old fossils revealed in South Africa in 2008. The fossils discovered by experts had a strange blend of humanlike and australopith features. Experts found that the species had a small brain but modern pelvic shape. This led experts to the idea that it was very probable that A. sediba is the species that eventually gave rise to Homo.
But not everyone agreed on the theory.
The new study basically focused on calculating the probability that experts discover a fossil from a human ancestor that is up to 800,000 years younger than a fossil from a descendant.
Taking into consideration the probable duration of each species’ presence on the planet, and the amount of time they may have coexisted, researchers determined that the scenario would happen a mere 0.09 percent of the time. “[O]ur models show that the probability is next to zero,” revealed Andrew Du and Zeresenay Alemseged of the University of Chicago in a press release.
However, fossils of A. afranesis have been dated back to around 3 Million years, and are closely related to the oldest Homo fossil.
Therefore, it makes much more sense that A. Afranesis is our direct ancestor and not A. sediba.
“Given the timing, geography, and morphology, these three pieces of evidence make us think Afarensis is a better candidate than sediba,” Alemseged concluded in the statement.