They are believed to have originated as modified gill arches, in much the same way as oral jaws. Originally hypothesized to have evolved only once,[1] current morphological and genetic analyses suggest at least two separate points of origin.[2][3] Based on connections between musculoskeletal morphology and dentition, diet has been proposed as a main driver of the evolution of the pharyngeal jaw.[4][5] A study conducted on cichlids showed that the pharyngeal jaws can undergo morphological changes in less than two years in response to their diet.[6] Fish that ate hard shelled prey had a robust jaw with molar-like teeth fit for crushing their durable prey. Fish that ate softer prey, on the other hand, exhibited a more slender jaw with thin, curved teeth used for tearing apart fleshy prey.[5] These rapid changes are an example of phenotypic plasticity, wherein environmental factors affect genetic expression responsible for pharyngeal jaw development.[6][7] Studies of the genetic pathways suggest that receptors in the jaw bone respond to the mechanical strain of biting hard-shelled prey, which prompts the formation of a more robust set of pharyngeal jaws.[7]