 Variations in the toolkit may have produced a large part of the morphological evolution of animals.The toolkit can drive evolution in two ways.A toolkit gene can be expressed in a different pattern, as when the beak of Darwin's large ground-finch was enlarged by the "BMP" gene, or when snakes lost their legs as "distal-less" became under-expressed or not expressed at all in the places where other reptiles continued to form their limbs.