We’re born of the ocean. Each of us begins life floating in amniotic fluid that has almost the same makeup as ocean water. Our earliest characteristics are fishlike. The month-old embryo grows fins first, not feet; it is one misfiring gene away from developing fins instead of hands. At the fifth week of a fetus’s development, its heart has two chambers, a characteristic shared by fish. Human blood has a chemical composition startlingly similar to seawater. An infant will reflexively breaststroke when placed underwater and can comfortably hold his breath for about forty seconds, longer than
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