Analysis of the impact of size and lineage on patterns of covariation in the life history traits of reptiles suggests that microevolutionary explanations, while perhaps necessary, are not sufficient to account for the patterns in the data. Patterns of covariation are strongly influenced by classwide correlations with a single trait, average adult female length; they are further influenced by the effects of family and genus, but the differences between the 2 orders of reptiles analyzed are entirely accounted for by the correlations with size. Thus, much of the tendency for traits to covary in the pattern originally thought to have been produced by r- and K-selection can be explained by selection on size alone followed by coadaptive shifts in life history traits. However, the pattern described here is also consistent with an adaptationist interpretation that would assert that both size and life history traits have been shaped by the same environmental conditions. In the residual variation, following the removal of correlations with size, there are significant effects of higher taxonomic levels, suggesting that lineage-specific differences in life histories, either constrained by or coadapted with morphological differences, can explain some of the tendency for life histories to be found in certain patterns.-from Author