[mlo]

why hasn't evolution allowed mother's birth canals to develop large enough for the increased brain size?

Evolution doesn't require perfection. God, on the other hand...

[gore3000]

Evolution doesn't require perfection. God, on the other hand...

...does not either. That's why even sinners go to heaven through His Grace.

[Bonaparte]

"Evolution doesn't require perfection. God, on the other hand..."

I'm afraid not, mlo.

I will greatly increase your pains in childbearing; with pain you will give birth to children. [Gen 3:16]

A few verses later, he lets us know that our bodies will break down, will die and return to the dust from which we came. All sorts of difficulties and breakdowns. And the Bible is full of such references.