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The statistical analysis of the fossil record shows that it is unlikely that Australopithecus sediba, a fossil of nearly two million years, similar to a turkey from South Africa, is the direct ancestor of Homo, the kind to which modern humans belong.
The research done by paleontologists at the University of Chicago, published this week in Progress of science, concludes by suggesting that Australopithecus afarensis, of the famous skeleton "Lucy", is still the most likely ancestor of its kind Homo.
The first A. sediba Fossils were discovered near Johannesburg in 2008. Hundreds of fragments of the species have been discovered since, each dating back about 2 million years. The oldest known Homo fossil, the jawbone of a species still unknown and found in Ethiopia, is 2.8 million years old. A. sediba 800,000 years old.
Despite this delay, the researchers who discovered A. sediba have claimed that it was an ancestral species Homo. Although it is possible that A. sediba (the hypothetical ancestor) could have postdated earlier Homo (the hypothetical descendant) 800,000 years old, the new analysis indicates that the likelihood of finding this timeline is highly improbable.
"It is quite possible that an ancestor's fossil differs later than that of a descendant," said lead author Andrew Du, PhD, who will join the faculty from Colorado State University after completing his postdoctoral research at Zeray's lab. Alemseged, PhD, Professor of Organism, Biology and Anatomy Donald Mc Pritzker at UChicago.
"We thought we were going a step further to ask what the probability of this would be, and our models show that the probability is close to zero," said Du.
Du and Alemseged also examined the scientific literature for other assumptions about ancestor-descendant relationships between two species of hominins. Of the 28 cases found, only one fossil of a descendant discovered for the first time was older than its proposed ancestor, a pair of Homo species separated by 100,000 years, much less than the 800,000 years separating A. sediba and earlier Homo. For the context, the average lifespan of a hominin species is about a million years.
"Again, we see that it is possible that an ancestor's fossil is later than that of his descendant," Du said. "But 800,000 years old, it's pretty long."
Alemseged and Du maintain that Australopithecus afarensisis a better candidate for the direct ancestor of HomoFor several reasons. The fossils of A. Afarensis date back three million years and are approaching the age of the first Homo jaw. Lucy and her counterparts, including Selam, the fossil of a A. afarensischild discovered in 2000, were discovered in Ethiopia, only a few kilometers from where Homo the jaw was discovered. The features of the jaw are also quite similar to those of A. Afarensis so that we can affirm that he was a direct descendant.
"Given the timing, the geography and the morphology, these three pieces of evidence make us think of a better strategy than the sediba," said Alemseged. "One may disagree about the morphology and the different characteristics of a fossil, but the level of confidence we can bestow on the mathematical and statistical analyzes of the chronological data in this article makes our argument very strong."
Source of the story:
Material provided by University of Chicago Medical Center. Original written by Matt Wood. Note: Content can be changed for style and length.
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