Sometimes when you take a look at life on Earth, it seems like evolution might be able to produce anything you could ever imagine. Can a mammal become so adapted to swimming in the ocean that it never comes back on dry land? Check. Can a squid evolve eyes as big as dinner plates? Check. Can a mole evolve a nose that acts like a hand? Check. But what about the fact that no ape has ever grown antlers? Or that no bird has ever reached a fifty foot wingspan? Or that, so far as anyone can tell, no animal has acquired hydrogen-producing bacteria in its gut and floated off like an airborne balloon? Are these dreams