K- and r- selection are terms that describe the effect of selection on so-called "life-history". A K- selective regime is an environment where selection pressures favour long generation times, small numbers of off-spring and greater specialisation. It is associated with stable environments. r- selective regimes, on the other hand, are associated with unstable environments, creating a general selection pressure that favours a fast generational turnover, large numbers of off-spring and a low degree of niche specialisation. Gould (1977) proposed that one might expect K-selective regimes to be associated with peramorphic evolution, as delaying the onset of maturity and increasing developmental time has the effect of lowering generational turnover. Similarly, in a r- selective environment, one would expect to find paedomorphosis as precocious maturation directly affects generation times. Since peramorphs tend to be larger than their ancestors, the incidence of Cope's rule size increases in K-selective regimes may be neatly explained by heterochrony.