The head size argument was also historically used as a reason to discriminate aganst women, since women in general have smaller heads than men. So obviously we're not as smart, right?
<sarcasm>
I have always understood brain folds to be the pertinent point to intelligence, not brain volume, just as Grinity suggests.
FWIW, my kids have relatively normal heads. Their whole bodies are on the big size--DS7 has always been 95th+ %ile for height and as a baby was always 95th %ile for weight. (Now he's a stringbean!) DS4 was never quite as big, but still always above the 75th %ile for height and also a heavy baby (who also leaned up as he got older). I think their heads were always in the 75th %ile or smaller.
So proportionally speaking, they probably have smallish heads, since their heads were always not-as-much-bigger-than-average as the rest of their bodies.
