In developed societies where caesarian sections are readily available to expectant mothers, evolutionary pressures should favor an increase in population head size. At least over evolutionary time, larger head size may be associated with greater intelligence and reproductive fitness but pelvic dimensions determine an upper limit to neonatal head size. Caesarian section allows both mother and baby to live (enabling and supporting baby's future reproductive fitness), allowing head size (and, perhaps, intelligence) to increase. Evolution is in full swing.

DSM 6/7/01