The relationship between the DVI, domain position and domain age. Left: Domain age and the DV I. OLD – domains that are common to all three main branches of life (Bacteria, Archea, Eukaryota); MID – domains that are present in all taxons of one of these branches (e.g. domains that can be found only in Bacteria, but not in Archea or Eukaryota); NEW – domains that are present only in one subgroup of one of these branches (e.g. domains that occur only in vertebrates). Right: DV I and position of the domain within the protein. NTERM – N-terminal domains; NTERM1 – next-to N-terminal domains in proteins with four domains or more; CTERM – C-terminal domains; CTERM1 – next-to N-terminal domains in proteins with four domains or more; MID – all remaining (non-terminal) domains; SINGLE – domains in single-domain proteins. On the y axis, domain versatility index (DV I). Bold line denotes the median; boxes denote the firstand second quartiles; whiskers show the minimum and maximum values not including outliers.