Some extreme examples include a medieval torture method in which the victim was blind-folded and tricked into perceiving that he/she was dying of blood loss, when the ‘‘blood’’ was merely warm water being poured over the skin - yet many victims died during this that was reminiscent of death from blood loss. Additionally, there is a case of a patient who attempted suicide by consuming pills he assumed were real, when they were in fact sugar pills. His blood pressure dropped dangerously low and required medical intervention.
What perplexes me is how and why this effect evolved as it has deleterious, occasionally deadly effects on the body. I would appreciate any theories.
The problem with this question is that evolution doesn’t really have a guiding instinct.
It would be more accurate, probably, to say that it was never selected against more than to say that it was selected for. That is, the conditions under which the nocebo effect are so deleterious to affect the propagation of the species are so rare (and likely came about so recently, on an evolutionary time scale) that it doesn’t matter one lick whether it happens or not.
In addition, it seems likely to me that it’s linked to the placebo effect. And linked in a manner I’m not convinced is separable – meaning no nocebo means no placebo either, and the placebo may end up being more of a net positive on a species-propagation scale than the nocebo is a net negative.
This is assuming, of course, that either have any real notable evolutionary advantage at all. I suspect (admittedly without evidence) that both of them are more of a weird quirky side effect of the more important evolutionary benefits like “a brain that has self awareness and capacity to reason and invent”. That is to say, placebo and nocebo might have minor benefits/detriments, but having them is linked to positives and negatives so much greater in the grand scheme of things that any effect they might have on a several million year species wide scale is just noise.
Interesting topic. I don’t have much to contribute except to suggest that the same question could be asked regarding the origins of somatoform disorders and other mental impairments that appear to have debilitating effects.
As to the evolution of deleterious characteristics, evolution is a messy process that leads to unintended side effects, in addition to the factors mentioned by Jragon. You might as well ask why humans evolved a psychoactive response to methamphetamines, when the reality is that the evolutionary history of the mammalian neurotransmitter systems are entirely independent of meth.
It is pretty clear that there is an evolutionary value in an organism reacting appropriately to it’s environment, and that our brain has a vital role to play in that process - detecting threats, priming us for fight-or-flight (or-freeze). It is this process that can produce effects in the body that match what we might think is going to happen. The events you describe fit on a continuum - from hyperresponsive (placebo/nocebo) to unresponsive (people with no concept of personal risk). Things may go badly at those extremes, but most people fit in the middle and are ok.
It is also clear that the fuzzy-matching process the brain uses does not always get things right, so there will be cases where a misunderstanding of the physical situation produces an invalid physiological response. And some people may have a stronger (or weaker) response than others (evolution likes the normal curve). But failures of the brain/body interface rarely actually kills us - and so doesn’t actually have much of an impact on evolution. So the evolutionary driver is the middle ground, but the outliers sometimes suffer. Of course, if selection criteria change (as environmental conditions change), then those outliers may become the new norm, and more evolution happens.
If you search ‘‘nocebo effect death’’ or related using a search engine, several results show up. One of the websites I visited mentioned the method I described.
I think the placebo and nocebo effects are related to the human capacity for imagination.
There is an obviouos evolutionary advantage to being able to imagine various scenarios before they occur and choosing what seems to be the wisest path before any of the possible events occur. For instance, when hunting a dangerous animal, you can strategize with your fellow hunters and put yourselves in the least dangerous position balanced against strategies based on the greatest chance of success.
This ability to imagine future events plays into the nocebo effect, where victims imagine the consequences so vividly, they actually suffer imagined harm.
Googling “Nocebo effect death blood loss” turns up nothing I can see related to the story of medieval torture simulating blood loss. What page did you find that story on?
I’m also a little skeptical about the original claims being true, though the nocebo effect in general is well-established.
But assuming these things are true, asking what the evolutionary purpose is strikes me as being equivalent to asking what the evolution purpose of broken bones is. It’s not the broken bones that serve a function. The bones themselves serve a function and they sometimes break. The fact that they break so rarely is what’s impressive, since it’s impossible to create an unbreakable object. In the overall measure of fitness, an animal with bones does better than one without bones, even when there’s a risk of breaking one. (Of course, this isn’t universal; some things do fine without bones, but let’s not sidetrack.)
So once we establish that the placebo effect has a benefit, then it pretty much follows that this mechanism has some flaws that could be detrimental under certain circumstances. That’s not surprising at all, and as long as the placebo effect results in more offspring than the alternatives, it still has a net enhancement on fitness.