In Sydney, geneticist and developmental biologist Pete Currie agreed that the nature and timing of the mutation “linked exquisitely” with the timing of evolutionary changes identified by paleontologists.
“This is the first window for looking into and seeing what it is about our genes that makes us human,” said Professor Currie, of The Victor Chang Cardiac Research Institute and University of NSW.
Generally, fossil experts conclude that hominids and chimps diverged about 2.4 million years ago. Hominids like Australopithecus afarensis and, later, Homo erectus appeared, leading to modern humans.
Writing today in the journal Nature, Professor Stedman and his colleagues claim that a tiny change to the so-called myosin heavy chain (MYH16) gene was enough to weaken our ancestral jaw muscles.
As a consequence, the hominid skull had room to shift shape, enabling it to accommodate an ever-enlarging brain. In contrast, chimpanzees were stuck with big, powerful jaws and, by necessity, much smaller brains.
According to Professor Currie, a “simple change” to muscle anatomy could indeed affect the skull.
“Altering the size of different muscles can produce dramatic alterations in the bones to which they attach,” he said.