Evolution could explain the placebo effect

[bananas]

http://www.newscientist.com/article/mg21528812.300-evolution-could-explain-the-placebo-effect.html

Evolution could explain the placebo effect
06 September 2012 by Colin Barras

ON THE face of it, the placebo effect makes no sense. Someone suffering from a low-level infection will recover just as nicely whether they take an active drug or a simple sugar pill. This suggests people are able to heal themselves unaided - so why wait for a sugar pill to prompt recovery?

New evidence from a computer model offers a possible evolutionary explanation, and suggests that the immune system has an on-off switch controlled by the mind.

It all starts with the observation that something similar to the placebo effect occurs in many animals, says Peter Trimmer, a biologist at the University of Bristol, UK. For instance, Siberian hamsters do little to fight an infection if the lights above their lab cage mimic the short days and long nights of winter. But changing the lighting pattern to give the impression of summer causes them to mount a full immune response.

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There is a simple explanation, says Trimmer: the immune system is costly to run - so costly that a strong and sustained response could dangerously drain an animal's energy reserves. In other words, as long as the infection is not lethal, it pays to wait for a sign that fighting it will not endanger the animal in other ways.

Nicholas Humphrey, a retired psychologist formerly at the London School of Economics, first proposed this idea a decade ago, but only now has evidence to support it emerged from a computer model designed by Trimmer and his colleagues.

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[Pterodactyl]

1. With evolution, all things are possible!