Leaving the land and becoming wholly aquatic was a bit like going into outer space. When we go into space we are weightless (not, by the way, because we are a long way from the Earth’s gravity, as many people think, but because we are in free fall like a parachutist before he pulls the ripcord). A whale floats. Unlike a seal or a turtle, which still comes on land to breed, a whale never stops floating. It never has to contend with gravity. A hippo spends time in the water, but it still needs stout, treetrunk-like legs and strong leg muscles for the land. A whale doesn’t need legs at all, and
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