Normalized dS and dN/dS values older and younger for older and younger Pre-SD and Post-SD duplicates. Normalized values were calculated as average postduplication branch values divided by the sum of average postduplication and preduplication branch values (A). Pre-SD set: differences in dS and dN/dS between younger and older duplicates were significant (P < 10⁻⁸ for dS and P = 0.01 for dN/dS, respectively, Wilcoxon’s test). Normalized dN/dS in older duplicates was not significantly different from the corresponding value in postspeciation branches (dN/dS Older-PostSp, P = 0.792 and dN/dS Younger-PostSp, P = 0.002, Wilcoxon’s test). (B) Post-SD set: only differences in normalized dS were significant (P < 10⁻⁹).