Keep out the cold

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One theory of human evolution is that our ancestors were semi-aquatic apes. They spent so much time in water that they lost their body hair, which impedes swimming. Daedalus points out that in fact, water is a deadly environment for human beings — not by drowning, but by chilling. Our alleged aquatic ancestors should have grown even thicker, longer fur to minimize heat transfer. Indeed, in a maritime accident, it is worth putting on all the clothes you can find; you will live that much longer in the water. As for swimming — forget it. It stirs away all the muscular heat it generates.

Sadly, many sea disasters happen so suddenly that there is no time to look for spare clothes. So Daedalus is devising a nautical uniform which reacts with water to form an ideal survival garment. His first inspiration was the absorptive ‘super slurper’ acrylate polymer used in bandages and babies' nappies. It can take up hundreds of times its weight of water, expanding into a flabby gel as it does so. In fibrous form, it can be woven into cloth. Underclothes of this fabric would swell in water into a splendid convection-proof wet-suit. But Daedalus's survival suit will not merely insulate; it will actively generate heat. He recalls the immersion batteries on aircraft life-jackets, which use sea water as their electrolyte, and power a signal lamp. His new garment will be one large distributed battery, triggered by immersion in water.

Its electrochemistry is an interesting challenge. At first Daedalus wanted it to generate hydrogen — perhaps enough of it to fill a balloon and lift the wearer out of the water. But more sanely, he now wants it to exploit the high energy of metal oxidation. A distributed zinc-air battery, exploiting the oxygen dissolved in the water, seems best. A few hundred grams of zinc could keep the wearer warm for hours in the coldest water. Hydrogen generated in a side reaction might usefully inflate buoyancy pockets in the garment.

Swollen by gas and absorbed water, the survival suit will usefully discourage attempts to swim. Its wearer may generate a little added heat by shivering, though this also will stir away all the metabolic heat thus mobilized. Only young babies can combat cold by passive thermogenesis. Advocates of our aquatic origins are welcome to the threadbare argument that their ability is a vestigial remnant of our ancestral watery metabolism.

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