from the AP:

WASHINGTON - Scientists think they have figured out why pregnant women don't lose their balance and topple over despite ever-growing weight up front. Evolution provided them with slight differences from men in their lower backs and hip joints, allowing them to adjust their center of gravity, new research shows.

This elegant engineering is seen only in female humans and our immediate ancestors who walked on two feet, but not in chimps and apes, according to a study published in Thursday's journal Nature.

Ha ha, suck it, men! And feminists, why don't you shut up for once. Don't get greedy.