Thanks for your input.
Any attempt over evolutionary time to add girth to the pelvic area would definitely compromise the ability to maintain bipedality and a steady gait.
Although the fontanelles do permit a shrinkage of the infant's skull during the birth process, they can only acccount for a variable amount. Since infants have been on the average increasing in size at birth due to such factors as better prenatal care,overall increase in the health of the mother, and an increase in overall body size from generation to generation, larger infants with increased cranial size has been the result.
I think that of the 8 lbs and 4 oz my daughter weighed at birth, it felt like the bulk of that weight was in her head.
I think that of the 8 lbs and 4 oz my daughter weighed at birth, it felt like the bulk of that weight was in her head I would expect - once the head and shoulders exit, the rest is a bit narrower. And I think you're quite right about rising birthweights as well.
Sometimes human intervention makes a difference - my wife attests that our daughter's birth, at 8 pounds, 8 ounces, was much easier than the first child, her older brother, at 6 pounds, 15 ounces. The difference was, she didn't have any drugs for the first one ;)