Researchers say they may have discovered the mutation that caused the earliest humans to branch off from their apelike ancestors, a gene that led to smaller, weaker jaws and bigger brains. Smaller jaws would have changed the structure of the skull by eliminating thick muscles that anchored a huge jaw to the crown of the head. The change would have allowed the cranium to grow larger and led to the growth of a bigger brain capable of making tools and language. The mutation is reported in the latest issue of the journal Nature by a team of biologists and plastic surgeons at the University of…