Fig. 4.

Absolute adult brain mass and hindlimb standing position as predictors of time to walking onset. (Left) Time to walking onset, log(WO), as a function of absolute adult brain mass, log(AbsBrM), and hindlimb standing position. Solid symbols and solid regression line represent species that can assume a plantigrade hindlimb standing position; open symbols and dashed regression line represent species that cannot assume a plantigrade hindlimb standing position (Table S2). Analysis of variance with covariance (ANCOVA) confirmed the overall robust main effect of adult brain mass as a covariate (F_(1,24) = 820.51, P < 0.0001, η² = 0.97) and revealed a main effect of hindlimb standing position as a grouping variable (F_(1,24) = 40.39, P < 0.0001, η² = 0.66). For the full model equation derived from multiple-regression analysis, R² values, and P values, see main text. The 95% confidence interval for R² was 0.95–0.99. (Right) The same as the Left panel, but with species indicated next to each data point for clarity. The Pearson correlation coefficient was 0.97 (two-tailed P < 0.0001; cf. Fig. S3). Axis units are as in Left but the x axis is expanded.