So many disturbing traits, once you look into them - sharks are the world's only known intra-uterine cannibals: eggs hatching within a uterus, the unborn young fight and devour each other until one well-adapted predator emerges. If the womb is a battleground, what then the sea? And, without the gas-filled bladders that float other fish, if sharks stop swimming, they sink. Thus their tendency to lurk along the bottom - 21-foot, 4,600-pound benthic land mines with hundred year life-spans. Dan Duane, Sharks