Why are giant pandas born so tiny?

(Duke University) Born pink, blind, and helpless, giant pandas typically weigh about 100 grams at birth -- the equivalent of a stick of butter. Their mothers are 900 times more massive than that. That raises a question that has vexed biologists: why the disparity? No one knows the answer, but by comparing bone growth across newborn bears, dogs and other animals, scientists find that one idea doesn't hold up.