Table 2.

Criteria of process homology based on various features of processes (see text for details).

feature of process	evidential criteria of process homology
parts	gene orthology; homology of cell types, tissues, organs (carries more weight for simple processes than complex processes)
	violated by: developmental system drift
outcome	homology criteria for structural features [90]: similarity (in special qualities), topological position, evidence of transitional forms
	violated by: co-option of processes into new roles
topological position	sameness of spatio-temporal position and relations with other processes within a life cycle
	violated by: heterochrony, heterotopy, serial homology
dynamical properties	morphological processes: same as ‘outcome’ above, but for temporally extended series of structural features
	morphogenetic processes: equivalence classes of configuration space topologies
	violated by: dynamically dissimilar but homologous processes
dynamical complexity	complexity of outcome (see ‘outcome’ above); phase space dimensionality; topological complexity of phase portrait; number of parts, number of dynamical modules
	violated by: dynamically simple homologous processes
transitional forms	plausible connectability of actually realized processes by trajectories in the same configuration space
	violated by: transitions not actually realized