Without the cumbersome chewing musculature, brains could grow bigger, marking the divergence of humans from apes.

• 有个发生在240万年前的基因突变，造成人类始祖下颚缩小，没有了笨重的咀嚼肌肉系统后，脑部可以长得更大，而划分了人类和猿类的差别。