Evolution of human pelvic size, head size and walking

[Will__]

A dinner party discussion turned interesting:

I put forward a theory I'd heard that says that during human evolution, pelvic size had to decrease to allow for normal bipedal walking. The theory states that both walking and an increasing brain size meant that human babies used to spend more time in the womb but through evolution spent less and less time there so that a) their brains (and thus heads) could be larger and b) humans could walk better with a narrowed pelvic aperture.

My friend refuted this; I don't know where I heard the theory but would love to know if anyone else had heard this or knows of its source. And does anyone know how much longer they used to spend in there?

Thanks.

[kwicky]

I have read that if you put a tape measure round the circumference of your head then multiply by 3 it will give your approx height.

[WaldoMcFroog]

Very approximate indeed if you happen to be a dwarf...

[Kinetic]

From what I remember reading in Bill Bryson's 'A Short History Of Everything' human pelvis size did indeed become smaller for us to become the masterful bipedal surveyors that we are; the drawback of this being much riskier labour and birth for mothers. Head size at birth did not change in relation to this as I don't think evolution could cater for such a convenience.

[Kinetic]

Sorry the book was 'A Short History Of Nearly Everything' :)

[mycats]

or read Babywatching by Desmond Morris

[mycats]

oops I meant "The Naked Ape" lol

[kwicky]

McFroog Have you tried measuring your head with a tape measure. I did it some years ago and it was correct to within a couple of inches. And I am not a dwarf! Instructions: Make sure the tape covers the forehead and the furthest distance at the back of the head.