Sons may be harder to birth than daughters in many mammals

News from Science reports that a study argues sons are harder to birth than daughters for many mammals, including humans and their ancient ancestors. That adds a wrinkle to the obstetrical dilemma, which links difficult human births to babies’ large heads and pelvises shaped for upright walking. The study suggests the added risk may have an evolutionary payoff: bigger male babies grow into bigger adults who tend to have more grandchildren.