Figure 1. Interplays among three major evolutionary trends. Three related evolutionary trends in human evolution: the relative increase in brain mass (A) predicts greater and more sophisticated behavioral plasticity (B), which in turn predicts longer dependence on parental care (C) due to prolonged learning needs. The diameter of maternal pelvic inlet (and width of birth canal) constitute a constraint (blue dotted lines) to: (i) prenatal growth of offspring brain; and (ii) maternal agility, including the vital ability to run for safety. The estimated time of appearance of bipedalism, tool utilization, and Neanderthal man are also depicted. See main text for further details.
