Literally ‘different measure’: a mechanism for generating changes in developmental outcomes that depends on the amount of expression of certain genes, and hence on the amount of the proteins they encode. Changes in such control mechanisms can produce significant morphological changes without any mutations in the proteins themselves, and have major evolutionary consequences. For example, the variations in beak shape and size among the different species of Galápagos finches (see darwin’s finches) are the result of variations in the amounts of two signalling proteins produced during embryonic development, bone morphogenetic protein 4 (BMP4) and calmodulin. High levels of calmodulin produce an elongated beak, while high levels of BMP4 produce a wide, deep beak. Compare heterochrony; heterotony; heterotypy.