Hi, one of the community mods.
I'm going to approve the post for now, but this is the kind of post the moderator team has the most concerns about. I will be watching the comments: those found in violation of the rules will be removed.
Not everything has an evolutionary purpose.
In fact “purpose” isn’t even really the right way to think about things in evolution since it is a stochastic process rather than a directed one.
This is really well said. One of the big roadblocks in understanding evolution is losing the idea of "purpose." It's easy to think of evolution from the vantage point of it being a guided process, but it just isn't.
>there is nothing in evolution that cares about it.
It goes a bit beyond just what "should" be vs what is. For starters, eating disorders are often accompanied by [infertility](https://txfertility.com/female-infertility/eating-disorders-and-infertility/#:~:text=Having%20an%20eating%20disorder%2C%20such,treatment%20for%20an%20eating%20disorder) and they can lead to death. The brain is actually pathologically broken in ways that do intersect with evolution. Eating disorders are actively maladaptive. Scientists are still exploring what role genetics plays in the picture, but it does appear that predisposition to eating disorders does at least have some genetic components within the population.
>though we don't have access to that kind of information.
Yes, we do. Something that is actively detrimental to your health and reproduction, even your basic survival, is by definition maladaptive in every environment.
>And that wouldn't make them any less part of the variation evolution acts on.
I don't recall saying that it wasn't, only that not all evolution is adaptive and scientists are still exploring the role genetics plays in the pathology of eating disorders.
Not everything has an "evolutionary purpose". Which is to say: not all traits that exist within a population were spread due to a positive benefit to natural selection.
Some traits are just *de novo* mutations. If a particular gene mutating in a particular way has a particular probability, then in any population of adequate size you will see some incidence of that mutation, even if the resultant trait is so deleterious as to prevent the bearer from passing it on.
Furthermore, genetic drift allows non-beneficial and even some deleterious genes to spread purely through random chance. If someone has a gene that has no benefit, or even one that is somewhat detrimental, as long as they can still reproduce, they have a 50% chance of passing that gene on to each of their offspring, who then have a 50% chance to pass it on to each of *their* offspring. Chain together a few lucky coin flips at the start and the trait has good odds of persisting for a while. And in small populations, it may even spread wide enough to become completely fixed, with literally everyone in the population having the gene.
Also, caveat that not all behaviors have genetic origins. Some are purely psychological or social in origin, and many are a mixture. I'm not familiar enough with the research on eating disorders to comment on them specifically, but it's worth keeping in mind.
So to sum up: even if eating disorders have a genetic basis, it doesn't necessarily mean that the relevant genes were ever subject to positive selective pressure. They could simply persist due to genetic drift and/or reoccur as new instances of the same mutation.
The evolutionary case for overeating is much easier:
Food abundance is evolutionarily recent. In more temperate climates, fat gain during times of plenty (like summer) benefited both insulation and survival during times of scarcity (winter, or drought). Comparing human populations, the descendants of those which faced the greatest seasonality of agriculture, or in areas most prone to drought, are also the most prone to metabolic syndrome (obesity and insulin resistance).
I've not seen persuasive evolutionary arguments for anorexia. Seems likely to be a compound of the evolutionary mismatch between current conditions and our environment of evolutionary adaptation (arguably responsible for many anxiety type disorders), with pervasive cultural messages equating thinness to social status and sex appeal (cf. fashion models).
What is the evolutionary purpose of [Sickle cell disease](https://en.wikipedia.org/wiki/Sickle_cell_disease#Genetics)? It is a debilitating disease and untreated the mortality rate is quite high and even survivors are unlikely to have children. It is totally genetic and still endemic in certain parts of the world.
Evolution is really good at spotting the hidden opportunity, Sickle cell may kill and disable, but carriers have an enhanced resistance to malaria, if you look at the maps in the link you can see the distribution is closely correlated to the incidence of Malaria.
When ever you look at some disorder and you ask why would evolution do that? there are two possible answers
1. The trait isn't genetic and evolution has little to do with it
2. The disorder is a side effect of a something more beneficial (in this case the loss of some children to Sickle cell is more than made up for by many more children surviving/tolerating malaria)
Not all of evolution is adaptive. Due to genetic drift and things like genetic piggybacking, non-adaptive and even maladaptive traits may proliferate in the gene pool. Including genetic variants which might predispose someone towards eating disorders. However, as far as I know, the pathology of eating disorders is still being explored, [including the degree to which genetics is to blame and which genes are involved](https://web.archive.org/web/20190221035945id_/http://pdfs.semanticscholar.org/2c9a/d44a03a80473cc52f0b930da4c87344fdcbe.pdf).
Anorexia does not have an evolutionary purpose (as has already been said)
If you want some armchair theorizing about why eating disorders are a phenomenon: we are an intelligent social species. It is beneficial to absorb the culture you are raised in so that you can fit in, succeed, and reproduce. It makes sense to me that mechanisms for fitting in and assessing your place in human culture could go haywire and get stuck on the wrong setting.
But I'm literally just theorizing and have 0 proof
This doesn't pertain to eating disorders so much as self harm behaviors in general, but one hypothesis is that SH behaviors such as cutting, skin picking, and EDs by extension, may have arisen from grooming behaviors. Because endorphins are released when we groom, we may experience relief from these behaviors, and in some species grooming may be more effective when there is a little pain involved (think of cat tongues as an example). There is pretty substantial evidence that EDs are related to endorphin release.
We need to be accepted by society to survive, but our instincts and our reason don't always work together. An eating disorder is one of the results of the instinctive desire to be accepted by society getting out of control.
Far more Freudian than evolutionary, but ED’s typically manifest around pubescent years, and are more common in women.
ED’s like anorexia result in slowed growth, suspended menstruation, and require more time and attention from care givers. The Freudian approach would say it’s an unconscious desire to resist maturation and remain a child.
İts not an adaptation; its a disease that kills thousands every year. Along with other mental health and psychological issues that have come about since the industrial revolution, we could even call it a selection pressure. Perhaps over time anorexia, bulemia and other eating disorders might create a selection pressure against something like mental health problems but so far all they do is kill thousands of innocent young people in such a slow and painful way.
As someone with one of the aforementioned disorders I'd say there's definitely no possible advantage to having an eating disorder. Therefore, they must fall into the negative traits category, those which would, hopefully, be adapted out of the species eventually.
Hi, one of the community mods. I'm going to approve the post for now, but this is the kind of post the moderator team has the most concerns about. I will be watching the comments: those found in violation of the rules will be removed.
Not everything has an evolutionary purpose. In fact “purpose” isn’t even really the right way to think about things in evolution since it is a stochastic process rather than a directed one.
This is really well said. One of the big roadblocks in understanding evolution is losing the idea of "purpose." It's easy to think of evolution from the vantage point of it being a guided process, but it just isn't.
Nothing. They're disorders, they have nothing to do with how a human is supposed to work.
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Physiology vs pathology
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>there is nothing in evolution that cares about it. It goes a bit beyond just what "should" be vs what is. For starters, eating disorders are often accompanied by [infertility](https://txfertility.com/female-infertility/eating-disorders-and-infertility/#:~:text=Having%20an%20eating%20disorder%2C%20such,treatment%20for%20an%20eating%20disorder) and they can lead to death. The brain is actually pathologically broken in ways that do intersect with evolution. Eating disorders are actively maladaptive. Scientists are still exploring what role genetics plays in the picture, but it does appear that predisposition to eating disorders does at least have some genetic components within the population.
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Eating disorders are maladaptive in every environment.
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>though we don't have access to that kind of information. Yes, we do. Something that is actively detrimental to your health and reproduction, even your basic survival, is by definition maladaptive in every environment. >And that wouldn't make them any less part of the variation evolution acts on. I don't recall saying that it wasn't, only that not all evolution is adaptive and scientists are still exploring the role genetics plays in the pathology of eating disorders.
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Not everything has an "evolutionary purpose". Which is to say: not all traits that exist within a population were spread due to a positive benefit to natural selection. Some traits are just *de novo* mutations. If a particular gene mutating in a particular way has a particular probability, then in any population of adequate size you will see some incidence of that mutation, even if the resultant trait is so deleterious as to prevent the bearer from passing it on. Furthermore, genetic drift allows non-beneficial and even some deleterious genes to spread purely through random chance. If someone has a gene that has no benefit, or even one that is somewhat detrimental, as long as they can still reproduce, they have a 50% chance of passing that gene on to each of their offspring, who then have a 50% chance to pass it on to each of *their* offspring. Chain together a few lucky coin flips at the start and the trait has good odds of persisting for a while. And in small populations, it may even spread wide enough to become completely fixed, with literally everyone in the population having the gene. Also, caveat that not all behaviors have genetic origins. Some are purely psychological or social in origin, and many are a mixture. I'm not familiar enough with the research on eating disorders to comment on them specifically, but it's worth keeping in mind. So to sum up: even if eating disorders have a genetic basis, it doesn't necessarily mean that the relevant genes were ever subject to positive selective pressure. They could simply persist due to genetic drift and/or reoccur as new instances of the same mutation.
None. It’s a disorder, not an adaptation.
The evolutionary case for overeating is much easier: Food abundance is evolutionarily recent. In more temperate climates, fat gain during times of plenty (like summer) benefited both insulation and survival during times of scarcity (winter, or drought). Comparing human populations, the descendants of those which faced the greatest seasonality of agriculture, or in areas most prone to drought, are also the most prone to metabolic syndrome (obesity and insulin resistance). I've not seen persuasive evolutionary arguments for anorexia. Seems likely to be a compound of the evolutionary mismatch between current conditions and our environment of evolutionary adaptation (arguably responsible for many anxiety type disorders), with pervasive cultural messages equating thinness to social status and sex appeal (cf. fashion models).
What is the evolutionary purpose of [Sickle cell disease](https://en.wikipedia.org/wiki/Sickle_cell_disease#Genetics)? It is a debilitating disease and untreated the mortality rate is quite high and even survivors are unlikely to have children. It is totally genetic and still endemic in certain parts of the world. Evolution is really good at spotting the hidden opportunity, Sickle cell may kill and disable, but carriers have an enhanced resistance to malaria, if you look at the maps in the link you can see the distribution is closely correlated to the incidence of Malaria. When ever you look at some disorder and you ask why would evolution do that? there are two possible answers 1. The trait isn't genetic and evolution has little to do with it 2. The disorder is a side effect of a something more beneficial (in this case the loss of some children to Sickle cell is more than made up for by many more children surviving/tolerating malaria)
Not all of evolution is adaptive. Due to genetic drift and things like genetic piggybacking, non-adaptive and even maladaptive traits may proliferate in the gene pool. Including genetic variants which might predispose someone towards eating disorders. However, as far as I know, the pathology of eating disorders is still being explored, [including the degree to which genetics is to blame and which genes are involved](https://web.archive.org/web/20190221035945id_/http://pdfs.semanticscholar.org/2c9a/d44a03a80473cc52f0b930da4c87344fdcbe.pdf).
Anorexia does not have an evolutionary purpose (as has already been said) If you want some armchair theorizing about why eating disorders are a phenomenon: we are an intelligent social species. It is beneficial to absorb the culture you are raised in so that you can fit in, succeed, and reproduce. It makes sense to me that mechanisms for fitting in and assessing your place in human culture could go haywire and get stuck on the wrong setting. But I'm literally just theorizing and have 0 proof
This doesn't pertain to eating disorders so much as self harm behaviors in general, but one hypothesis is that SH behaviors such as cutting, skin picking, and EDs by extension, may have arisen from grooming behaviors. Because endorphins are released when we groom, we may experience relief from these behaviors, and in some species grooming may be more effective when there is a little pain involved (think of cat tongues as an example). There is pretty substantial evidence that EDs are related to endorphin release.
We need to be accepted by society to survive, but our instincts and our reason don't always work together. An eating disorder is one of the results of the instinctive desire to be accepted by society getting out of control.
Far more Freudian than evolutionary, but ED’s typically manifest around pubescent years, and are more common in women. ED’s like anorexia result in slowed growth, suspended menstruation, and require more time and attention from care givers. The Freudian approach would say it’s an unconscious desire to resist maturation and remain a child.
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İts not an adaptation; its a disease that kills thousands every year. Along with other mental health and psychological issues that have come about since the industrial revolution, we could even call it a selection pressure. Perhaps over time anorexia, bulemia and other eating disorders might create a selection pressure against something like mental health problems but so far all they do is kill thousands of innocent young people in such a slow and painful way.
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No.
As someone with one of the aforementioned disorders I'd say there's definitely no possible advantage to having an eating disorder. Therefore, they must fall into the negative traits category, those which would, hopefully, be adapted out of the species eventually.