According to scientists, the placebo effect is an ancient evolutionary mechanism that allows the nervous system to control the strength of the immune response.
Everyone knows the essence of the placebo effect: a person thinks that he has drunk the medicine and recovers, although in fact, under the guise of a real pill, he was slipped a snag. But where did we get this "option" - to respond to a placebo? Why does false medicine have the desired effect? What evolutionary considerations could this strange phenomenon arise from?
Biologists have long pondered this mystery, but the first hypotheses to explain it appeared about ten years ago, when it became clear that animals also have something similar to the placebo effect. If the Dzungarian hamsters were kept in winter lighting, that is, they imitated a short day and a long night, then the animals' immunity reacted sluggishly to the infection.
If they were given summer lighting, their immune systems were aroused quite strongly for the infection. A similar difference in the immune response was observed in people who received a placebo: their immunity responded to the disease twice as strong. It turned out that the immune system was guided by data from the brain about what was happening outside.
At the same time, it was suggested that in the case of a weak infection, it is more beneficial for the body not to trigger a full-fledged immune response. A strong immune response, firstly, consumes a lot of resources, and secondly, it can indirectly damage the body itself. Therefore, in order not to shoot sparrows from cannons, immunity awaits a really serious danger, and insignificant cases of invasion of pathogens are allowed to take their course. If at the same time the body suddenly feels some kind of help from the outside, the immune system wakes up.
In the case of hamsters, the extended day length corresponds to summer time, which is a season rich in food. This means that there is no shortage of resources, and they can be spent on the immune response. In the case of a placebo pill, the brain infers that the infection will be weakened by medication and the immune system will be able to deal with it more easily. That is, the immune response will be short-lived and not too costly.
However, all this reasoning remained a hypothesis for a long time, until researchers from the University of Bristol (UK) created a mathematical model to confirm it. An article describing this model was published in the journal Evolution and Human Behavior. It should be said right away that the researchers relied not so much on physiology as on evolution and ecology. They showed that under changing environmental conditions, animals will live the longer and the more offspring they will leave, the less often they will trigger an immune response. Conversely, if the environment is constant and supportive of its inhabitants, then the evolutionary success of an individual depends on how quickly his immune system can expel the infection from the body. That is, in conditions of crisis and instability, it is more profitable to maintain a positional war with infection,delaying the decisive immune strike to the last.
In conditions of peace and prosperity, the sooner the immune system gets rid of the infectious trouble, the better. This provides an evolutionary rationale for placebo: the pill is seen as outside help, as the onset of favorable conditions.
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In the last 10 thousand years, man has been trying in every possible way to provide himself with stable conditions and has even been very successful in this. However, our subconscious, apparently, is not yet fully accustomed to the changed world, as evidenced by the continued ability to respond to placebo. It is worth paying special attention to the fact that this hypothesis suggests a link between immunity and higher nervous activity.
Of course, skeptics can say that we are talking about theoretical, computer-mathematical proof. However, we recall that extremely similar results were obtained not so long ago in a completely experimental work, in which researchers studied the influence of the nervous system on the development of an allergic reaction in humans.