Brain weight generated per gestation day is considerably greater for high-GI than low-GI species.
(A) Density plot showing the frequency of occurrence of the 96 eutherian species listed in Table S1 (omitting C. volans) with GI values of ≤1.5 (blue) and >1.5 (red) as a function of ln-transformed brain weight generated per gestation day. Note that the smallest values for brain weight per gestation day are found only in the low-GI group, while the largest values are found only in the high-GI group, but that the mean values for the two groups is also significantly different (dashed blue and red lines, T = 5.16, degree of freedom [d.f.] = 41, p = 4×10−5). (B) Ln-transformed plot of brain weight generated per gestation day for the 96 mammalian species (see A). Dashed blue line, mean value for GI≤1.5 (−2.04±0.047, standard deviation [SD]); red dashed line, mean value for GI>1.5 (0.583±0.050, SD). Selected organisms are indicated. The colors of the various high-GI and low-GI species shown above and below the plot, respectively, indicate the taxonomic groups as shown in Figure 1; the sequence of high-GI and low-GI species from left to right is according to Table S1, column A, top to bottom. Brain weight per gestation day was calculated from the data shown in Table S1, columns C and M.
