Archaeology news: Discovery of ancient human fossil reveals minute evolutionary change

A species of extinct human evolved rapidly some two million years ago, paving the way for modern humans. It was thought that the species, known as Paranthropus robustus, were similar to other primates – including characteristics such as the males being typically larger. But a new fossil discovery in South Africa shows the P Robustus rapidly changed as a result of drastic climate change.

Scientists already knew that P Robustus appeared at roughly the same time as Australopithecus, a primitive being from the Homo genus of which modern humans belong to, went extinct.

Now, a discovery of a “remarkably well preserved” fossil of a male P robustus in Drimolen, South Africa, shows that climate and environmental changes sped up the species evolution.

The team believe P Robustus evolved rapidly to adapt to its surroundings, according to the research published in the journal Nature Ecology & Evolution.

The researchers state that the species came into fruition over just tens of thousands of years, as opposed to the millions which it usually takes a species to evolve.

David Strait, professor of biological anthropology in Arts & Sciences at Washington University, said: “This is the type of phenomenon that can be hard to document in the fossil record, especially with respect to early human evolution.

“The working hypothesis has been that climate change created stress in populations of Australopithecus leading eventually to their demise, but that environmental conditions were more favourable for Homo and Paranthropus, who may have dispersed into the region from elsewhere.

“We now see that environmental conditions were probably stressful for Paranthropus as well, and that they needed to adapt to survive.”

Evolution in one species can be hard to spot, especially when there are missing items from the fossil record.

However, as the specimen, which has been dubbed DNH 155, is so well preserved, scientists have been able to notice the more minute changes.

The newly discovered specimen is much larger than previous records of P. Robustus found at Drimolen but smaller than males of the same species discovered at Swartkrans.

Jesse Martin, a doctoral student at La Trobe University and the co-first author of the study, said: “It now looks as if the difference between the two sites cannot simply be explained as differences between males and females, but rather as population-level differences between the 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.

“One can use the fossil record to help reconstruct the evolutionary relationships between species, and that pattern can provide all sorts of insights into the processes that shaped the evolution of particular groups.

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“But in the case of P robustus, we can see discrete samples of the species drawn from the same geographic region but slightly different times exhibiting subtle anatomical differences, and that is consistent with change within a species.”

Angeline Leece of La Trobe University, the other first author of the study, added: “It’s 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 size changes over time in the species, which begs the question of why.

“There are reasons to believe that environmental changes placed these populations under dietary stress, and that points to future research that will let us test this possibility.”

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