Morphogenera, monophyly, and macroevolution.

Jablonski and Finarelli (1) suggest that morphogenera, even when they are nonmonophyletic, serve as good representatives for large-scale evolutionary studies. We feel there are two issues that warrant further discussion. First, the test used to evaluate the effect of using nonmonophyletic groups for macroevolutionary studies was not conservative and thus does not provide strong evidence about the impact of nonmonophyly on evolutionary studies. Their test examined whether the median trait value for the species in a nonmonophyletic genus correlated with the median trait value for those same species plus the additional species needed to make the set monophyletic. Correlation of the median value of a set of measurements with the median value of a superset of those measurements is to be expected (as is brief ly mentioned in the methods section of ref. 1). To demonstrate this, we correlated the median values of ln body mass from random sets of 3, 7, and 15 mammal species and 0 –30 additional species for 45 simulated genera, using data from ref. 2 (Fig. 1A). Even when the median of 3 species is correlated with those 3 plus 15 additional species , the correlation is significant. Moreover, slightly better than random assignment of species to genera increases the expected correlation. To show this, we compare the results of figure 3A from ref. 1 with simulations where 45 genera of 3 species each were created from species chosen randomly from (i) the same family (Fig. 1B) and (ii) the same order (Fig. 1C) (data from refs. 2 and 3). Correlations between morphogenus median and the smallest clade containing the morphogenus species were significant (P Ͻ 0.0001). Thus, the observed correlations presented in ref. 1 are not surprising. Second, ref. 1 also appears agnostic as to whether the mor-phogenera should be used together with a phylogeny when Fig. 1. Correlation analyses of morphogenera and comparative analysis of body mass and gestation. (A) Significance (Spearman correlation, as in ref. 1) of correlation of means of ln body mass of a set of X species with a set of X ϩ Y species (solid lines), where X is 3 (closed circles), 7 (triangles), or 15 (open circles) and Y is 0, 5, 10, 15, 20, 25, 30, where the larger set includes all the species in the smaller set. Dotted lines correspond to correlating a set X with a set Z ϩ Y species, where the size …