(p. D4) Around two million years ago, this area in South Africa is believed to have undergone a chaotic climate shift. The regional environment transformed from wetter and more lush conditions to drier and more arid ones. In order for a species like P. robustus to survive in such terrain, it probably would have needed to be able to chew on tough plants. But the specimen found in the cave at Drimolen didn’t seem to fit with what some scientists had previously stated about the human cousin.
They labeled the skull DNH 155 and determined that it belonged to a male.
. . .
In addition to being smaller than male P. robustus who lived at Swartkrans, DNH 155’s cranium indicated its chewing muscles were not as strong as theirs. Mr. Martin said the differences suggest DNH 155 and the other P. robustus found at Drimolen were smaller not because they were all female, but rather because they were earlier forms of the species belonging to a different population that hadn’t yet been subjected to the environmental pressures that would favor larger sizes and stronger jaw muscles.
“It basically hasn’t become this massive chewing and grinding machine that it becomes later,” Mr. Martin said.
The change would have been the result of microevolution, or an evolutionary change occurring within a species. Such a morphological change, the scientists said, was likely the result of P. robustus adapting to that changing climate, with members of the species who were able to get enough nutrition from a change in their food supply surviving, and passing their traits to offspring.
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(Note: the online version of the story has the date Nov. 9, 2020, and has the title “How a Human Cousin Adapted to a Changing Climate.”)