Book Summaries health

Chapter 3: The Power of Parasites (The Red Queen)

The Red Queen’s first prophet, Leigh Van Valen, was a devout student of evolution. In 173, he was searching for a phrase to express a new discovery he had made while studying marine fossils. The discovery was that chances that a family of animals goes extinct does not depend on how long that family has existed. Species do not get better at surviving. And unlike individuals, they do not grow feeble with age. Their chances of extinction are random.

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Van Valen knew the significance of his discovery. The vital truth that escaped even Darwin, but not Van Valen, was that the struggle for existence never gets easier. No matter how well a species adapts to its environment, it cannot relax, since competitors and enemies are adapting to their niches. Survival is a zero-sum game.

Success only makes one species a more tempting target for another species. The phrase ‘The Red Queen’ comes from Van Valen’s memory of Alice in Wonderland. In the story, Alice encounters living chess pieces beyond the looking glass. The Red Queen is a formidable woman who runs like the wind but never seems to get anywhere:

‘Well, in our country,’ said Alice, still panting a little, ‘you’d generally get to somewhere else – if you ran very fast for a long time, as we’ve been doing.’ ‘A slow sort of country!’ said the Queen. ‘Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!’

Matt Ridley, The Red Queen

The Red Queen has become famous, and no more is it more reputable than in theories of sex. Red Queen theories hold that the world is competitive to death. Although it changes, although species do run, they stay in the same place.

The world does not progress, despite change. Sex, according to Red Queen theory, has nothing to do with adapting to the physical world by becoming bigger, or more camouflaged, but is all about combating the enemy that fights back. Biologists have overestimated the importance of physical causes of premature death rather than biological ones. Natural disasters usually loom large in theories of evolution. And marvel’s of physical adaptation such as the camel’s hump are given as proof of evolution’s great achievements. The first ecological theories of sex were about explaining this adaptability.

But animals don’t die because of physical factors. More often, it is other creatures such as parasites, predators, and competitors that kill them. A water flea starving in a crowded pond is not a victim of food shortage but of competition. Predators and parasites likely cause most of the world’s deaths in some way.

You ancestors were more likely to be victims of smallpox, tuberculosis, influenza, pneumonia, plague, scarlet fever, diarrhea. Starvation or accidents may have made people weaker, but infection killed them.

The ‘great war’ of 1914– 18 killed twenty-five million people in four years. The influenza epidemic that followed it killed twenty-five million in four months. 23 It was merely the latest in a series of devastating plagues

Europe was laid waste by measles after AD 165, by smallpox after AD 251, by bubonic plague after 1348, by syphilis after 1492, by tuberculosis after 1800.24 And those are just the epidemics. Endemic diseases also carried away further vast numbers of people.

Evolutionary biologists have found themselves again returning to the theme of parasites. As Richard Dawkins put it in a recent paper: Eavesdrop [over] morning coffee at any major centre of evolutionary theory today, and you will find ‘parasite’ to be one of the commonest words in the language.

Parasites are touted as the prime movers in the evolution of sex, promising a final solution to that problem of problems. Parasites have a deadlier effect than predators for two reasons. One is that there are more of them. Human beings have no predators except great white sharks and each other, but they have lots of parasites.

The second reason, which is the cause of the first, is that parasites are usually smaller than their hosts while predators are usually larger. This means that the parasites live shorter lives and pass through more generations in a given time than their hosts. The bacteria in your gut pass through six times as many generations during your lifetime as people have passed through since they were apes. As a consequence, they can multiply faster than their hosts and control or reduce the host population.

Parasites and their hosts are locked in a close evolutionary embrace. The more successful the parasite’s attack (the more hosts it infects or the more resources it gets from each), the more the host’s chances of survival will depend on whether it can invent a defence. The better the host defends, the more natural selection will promote the parasites that can overcome the defence. So the advantage will always be swinging from one to the other: the more dire the emergency for one, the better it will fight. This is truly the world of the Red Queen, where you never win, you only gain a temporary respite.

"Silence is the best expression of scorn" - G.B. Shaw

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