Table 1.

Summary of examples. Ontogenetic processes represent a distinctive level of organization (highlighted in italics). The distinctive pattern of conservation across these examples indicates that evolution at this ‘process’ level is (at least partially) dissociable from evolution at other levels, and is thus amenable to classification in terms of process homology.

conservation/homology at level	vertebrate somitogenesis	insect segmentation	cyclorrhaphan segmentation	sea urchin larval skeleton
phenotypic outcome	yes	yes	yes	no
ontogenetic process	yes	yes or noa	yes	yes
genetic network	partial	partial	yes	yes
individual genes	partial	partial	partial	yes
sequence level	unknown	no	no	unknown

^aDepending on phylogenetic scope (see text).