[marco_salvatori]

My take away was that researchers produced evidence that the shape of bird eggs is optimized, around physical characteristics of the parent. I am open to the idea and sceptical. In the context of humans it would be like saying the shape of children is optimized around the physical characteristics of a womans body, as opposed the the supposition that a womans body is optimized around the physical characteristics of children it will have to give birth to.

[Terretta]

Ha, literal "chicken and egg" framing.

OK, your idea is parent optimized for physical characteristics of progeny, or in this case, the parent is formed by the egg, not the egg by the parent?

In this article, your point would be, because of laying conical eggs, certain species of birds were able to nest on cliffs. So their eggs not rolling made them cliff dwellers?

And similarly, elliptical eggs optimized their mothers for faster flight?

Not sure. Put like that, I'm thinking it's reasonable the parent trying to roost on the cliff came first.

[pjc50]

Well, they're competitively co-evolved; human head size at birth really is limited by maternal survivability.

[empath75]

Children are in fact born well before the level of development other mammals reach before birth and with soft skulls so they can fit through the opening.