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An extinct human species evolved rapidly about two million years ago, paving the way for modern humans. The species, known as Paranthropus robustus, was thought to be similar to other primates, including features such as males that are typically larger. But a new fossil discovery in South Africa shows that P Robustus has changed rapidly due to drastic climate change.
Scientists already knew that P Robustus appeared around the same time that Australopithecus, a primitive being of the genus Homo to which modern humans belong, went extinct.
Now, a discovery of an “extraordinarily well-preserved” fossil of a male P robustus in Drimolen, South Africa, shows that climate and environmental changes have accelerated the evolution of species.
The team believes P Robustus evolved rapidly to adapt to its surroundings, according to research published in the journal Nature Ecology & Evolution.
Researchers say the species materialized in just tens of thousands of years, unlike the millions it usually takes for a species to evolve.
David Strait, professor of biological anthropology in Arts & Sciences at Washington University, said, “This is the kind of phenomenon that can be difficult to document in the fossil record, especially compared to early human evolution.
“The working hypothesis was that climate change created stress in Australopithecus populations which ultimately led to their demise, but that environmental conditions were more favorable for Homo and Paranthropus, who may have dispersed to the region from elsewhere.
“Now we see that the environmental conditions were probably stressful for Paranthropus as well, and that they needed to adapt to survive.”
Evolution in a species can be difficult to spot, especially when elements of the fossil record are missing.
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However, because the sample, which was dubbed DNH 155, is so well preserved, the scientists were able to notice the most minute changes.
The newly discovered specimen is much larger than previous P. Robustus records found at Drimolen but smaller than the males of the same species discovered at Swartkrans.
Jesse Martin, a PhD student at La Trobe University and co-first author of the study, said: “It now appears that the difference between the two sites cannot be explained simply as differences between males and females, but rather as a population. – level differences between sites.
‘Our recent work has shown that Drimolen predates Swartkrans by about 200,000 years, so we believe that P robustus evolved over time, with Drimolen representing an early population and Swartkrans representing a later, more anatomically derived population.
‘The fossil record can be used to help reconstruct evolutionary relationships between species, and that model can provide all sorts of insights into the processes that have shaped the evolution of particular groups.
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‘But in the case of P robustus, we can see discrete specimens of the species from the same geographic region but slightly different times that show subtle anatomical differences, and this is consistent with change within a species.’
Angeline Leece of La Trobe University, the other first author of the study, added: “It is very important to be able to document evolutionary change within a lineage.
“It allows us to ask very focused questions about evolutionary processes.
“For example, we now know that tooth sizes change over time in the species, which raises the question of why.
“There are reasons to believe that environmental changes have placed these populations under food stress, and this points to future research that will allow us to test this possibility.”
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