From S Caroll, “Many approaches are being taken, and a few intriguing associations of candidate genes and the evolution of particular traits have been discovered, such as the…MYH16 muscle-specific myosin pseudogene and the evolutionary reduction of the masticatory apparatus.”
Powerful masticatory muscles are found in most primates, including chimpanzees and gorillas…. In contrast, masticatory muscles are considerably smaller in both modern and fossil members of Homo. …Here, we show that the gene encoding the predominant myosin heavy chain (MYH) expressed in these muscles was inactivated by a
frameshifting mutation after the lineages leading to humans and chimpanzees diverged. Loss of this protein isoform is associated with marked size reductions in individual muscle fibres and entire masticatory muscles. Using the coding sequence for the myosin rod domains as a molecular clock, we estimate that this mutation appeared approximately 2.4 million years ago.