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Mental Disorders And Evolution: What Would Darwin Say About Schizophrenia?

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Published: November 16, 2012 by David Schultz

It's a question that's baffled evolutionary theorists for decades: if survival of the fittest is the rule, how have the genes that contribute to serious, debilitating mental disorders survived?

It's been shown that people who suffer from schizophrenia, autism, anorexia and other disorders are less likely to have children. And yet, the genes that cause these disorders aren't going away. In fact, some of the disorders appear to be becoming more common. Evolutionary theory wouldn't predict that.

Scientists have a few theories that attempt to explain this paradox.

One is that the genetic mutations that cause these disorders occurred relatively recently, so not enough generations have passed to allow the evolutionary process to weed them out.

Another theory is that the genetic mutations that cause a disorder in one person somehow make that person's sibling more likely to have children. In a situation like that, the mutation offers a net benefit to a person's family.

A team of Swedish and British scientists recently tested these theories by comparing the rates at which people suffering from mental illness have kids to those of their siblings. The data came from a medical database of more than 2 million Swedes.

The researchers found that the siblings of people who suffer from schizophrenia, autism and anorexia had on average the same or fewer children than the general public, which would seem to confirm the first theory. But they also found that the siblings of people who suffer from depression or substance abuse had significantly more children than the general public, an outcome more in line with the second theory.

We talked with Dr. Peter McGuffin, a professor at King's College London who worked on the study, which was published in the journal Archives of General Psychiatry. Here are highlights from the interview, edited for length and clarity.

Q: You say at the beginning of your paper that "psychiatric disorders have long puzzled researchers by defying the expectations of natural selection." Why?

A: It's particularly the case with schizophrenia, which in this paper and in many other papers has been shown to be a disorder that drastically reduces your fecundity — the number of kids you have. It's often referred to as reduced fertility but, strictly speaking, people with schizophrenia aren't infertile. It's just that they're less often likely to find a partner and have kids.

Schizophrenia is estimated to have a heritability of around 80 percent. Same is true for autism. So if these disorders are very heavily influenced by genes, but the people who have the disorders are less likely to pass on their genes, why aren't the disorders becoming less common in the population?

Q: What are some of the theories as to why this might be going on?

A: There are other gene disorders that have selection pressures against them, but are maintained in the population. A brilliant example of that is sickle cell disease. If you have sickle cell disease, the chances are if it's untreated it's going to kill you before you reach early adult life. Whereas, if you have the sickle cell trait — which is to say, you have one copy of the gene, not two copies — it protects you against malaria if you happen to live in an area where malaria is rife. So there's a selective disadvantage to having the disease, but there's a selective advantage to having the trait.

Q: Your study looked at not just people who were affected by psychiatric disorders, but also their siblings. Why?

A: The hypothesis would be that the relatives of the people who have the disorder, who don't actually have the disorder themselves, are compensating by having more children. I mean, not deliberately compensating by going out and having more children, but there's just something about their makeup that makes them have more kids.

So that's essentially what we were testing in this paper. We were looking at the fecundity of schizophrenics, which we found to be low, as was the fecundity of people with autism. The question is, do their relatives actually make up for this by having more kids because they're advantaged in some way? And the answer is no in the case of schizophrenia, but yes in the case of depression.

Q: If I'm someone who is the sibling of someone who has a psychiatric disorder, what do I need to know? Do I need to think twice about having biological children?

A: You need to know you'll have an increased risk of getting the disorder yourself compared with the general population. The risk in siblings is increased, but it's not increased so dramatically that it ought to stop you from having kids.

These aren't single-gene disorders. These are complex disorders where being a relative is just a risk factor, not a certainty factor.

Q: So ultimately, if I'm the sibling of someone who has one of these disorders, I should be aware of the risks, but it's not something that would make me say "I'm not going to have children."

A: It shouldn't make you say that. And if you are particularly concerned about it and you have more than one relative affected by it in the family, it might be worth seeking [genetic] counseling from an expert who knows what the risks are. [Copyright 2012 National Public Radio
Posted on CafeMom Mobile
by on Nov. 16, 2012 at 8:14 PM
Replies (11-20):
Clairwil
by Ruby Member on Feb. 23, 2013 at 3:00 AM
Quoting LoganTroyMom:

why is this even a question?

in our culture, even the dead can be kept alive (life support). where, in that, does evolution fit in? we have disrupted nature to it's fullest and it's certainly one of our many issues.. at the same time, i don't condone just letting the disabled die as that is not humane, but nature is not always so humane.

Just because our society no longer allows people to die of starvation, that doesn't mean there isn't still a strong selective force.

What matter is not if some individuals die, but rather if all individuals have the same number of offspring.

They don't.

How many of your friends or relatives do you know of, who don't have children, or didn't even get married?

Clairwil
by Ruby Member on Feb. 23, 2013 at 3:33 AM
Quoting stormcris:

It seems many of the people who were deemed great in history were also decided to have some sort of mental illness including Darwin. What does that say about genius/intelligence and mental illness?

"Mad Genius" makes for good headlines, but actually the correlation is inverse.

See the results on page 10 of:

http://www.groups.psychology.org.au/Assets/Files/IQ-and-Mental-Illness-12Aug2010.pdf


stormcris
by Christy on Feb. 23, 2013 at 4:00 AM

Would this suggest that the lower the IQ the more primative the brain thus the heightened reaction to various mental illness because of a lack of coping skills?

Quoting Clairwil:

Quoting stormcris:

It seems many of the people who were deemed great in history were also decided to have some sort of mental illness including Darwin. What does that say about genius/intelligence and mental illness?

"Mad Genius" makes for good headlines, but actually the correlation is inverse.

See the results on page 10 of:

http://www.groups.psychology.org.au/Assets/Files/IQ-and-Mental-Illness-12Aug2010.pdf



Clairwil
by Ruby Member on Feb. 23, 2013 at 4:38 AM
Quoting stormcris:
Quoting Clairwil:

See the results on page 10 of:

http://www.groups.psychology.org.au/Assets/Files/IQ-and-Mental-Illness-12Aug2010.pdf

Would this suggest that the lower the IQ the more primative the brain thus the heightened reaction to various mental illness because of a lack of coping skills?

I don't know.

I don't have sufficient data to make even a 'better than random' guess.

stormcris
by Christy on Feb. 23, 2013 at 5:22 AM

Thanks

Quoting Clairwil:

Quoting stormcris:
Quoting Clairwil:

See the results on page 10 of:

http://www.groups.psychology.org.au/Assets/Files/IQ-and-Mental-Illness-12Aug2010.pdf

Would this suggest that the lower the IQ the more primative the brain thus the heightened reaction to various mental illness because of a lack of coping skills?

I don't know.

I don't have sufficient data to make even a 'better than random' guess.


lancet98
by Silver Member on Feb. 23, 2013 at 7:54 AM
2 moms liked this

 

It doesn't say much at all!  It's just one more facet of the ridiculous, ignorant view of mental illness that the media (and our own agendas) can create.

 In fact, the lives of intelligent people with mental illness are quite often presented to the public with an extremely distorted lens - I won't even get started on the truth about people like John Nash, but it is nothing at all like what the media has made of it.

Both the public and its media has a rather morbid fascination with intelligence and mental illness and other disabilities.   What is not covered is that mental illness can develop in anyone of any intelligence level, and that it can be particularly disabling if it occurs early in life or in a person who has other disabilities as well.

But it is also no respector of intelligence.  Intelligent people are not spared in any way by this disease.   It is an 'equal opportunity' disease.  

Such facts can mislead people to believing that mental illness is some sort of darling adventure.  Try to convince me of that when someone calls me up at 2 am sobbing because some horrible apparition is trying to hurt them, or when a wife calls me up and sobs that her husband does nothing but stare out the window these days, and won't accept any help.  Tell that to the mom who still has PTSD from coming home and finding her son dead in her kitchen, after his efforts to dig out both of his eyes with a steak knife, with blood sprayed everywhere, even on the ceiling.

 In fact mental illness involves suffering and measurable, physical changes in the brain's chemistry, activity and structure that can be see on things as simple and basic as a PET scan, an MRI or an EEG.

 It's even caused some people to advocate criminalization of mental illness(it doesn't exist, so any time a mentally ill person does something wrong, it's a result of 'poor moral choices', so plunk 'em in jail and don't give 'em any treatment) and non-treatment of mental illness.

Myself, I won't even go there.   Mental illness is not some fun journey of self discovery - it involves individual suffering and brain deterioration when not treated.   When RD Laing claimed it was some journey of self-discovery, Mark Vonnegut, who may have had schizophrenia or at least some form of temporary psychosis, said, 'The only thing that you can do with a guy like Laing is BITE HIM'.   And he was RIGHT!

What mental illness does NOT involve is some inevitable monstrosity of violence - the vast majority of mentally ill people never hurt anyone - except themselves.   What it does not HAVE to involve is inevitable deterioration and loss of quality of life.

The public needs to arrive at some sort of sensible middle ground, in which the mentally ill are not reviled or viewed as 'evil', OR viewed as charmed and magical, but are viewed as regular decent people who suffer from a brain disease that is potentially very disabling, if untreated.

Quoting stormcris:

It seems many of the people who were deemed great in history were also decided to have some sort of mental illness including Darwin. What does that say about genius/intelligence and mental illness?

 

 

momtoscott
by Platinum Member on Feb. 23, 2013 at 8:02 AM
2 moms liked this

 Interesting article and even more interesting responses.  Thanks for posting. 

One thing that annoys me is when people attribute a "purpose" to evolution and then say something undercuts that (often as some kind of argument for a creator with a better plan).  A set of cumulative effects does not necessarily indicate any underlying intent! 

lancet98
by Silver Member on Feb. 23, 2013 at 8:29 AM

 

It suggests nothing of the kind.   Lower intelligence does NOT involve a 'more primitive brain' at all.   Such theories belong in the garbage can and nowhere else.   They have led to prejudice and eugenics and are nothing more than disgusting.

In fact, most developmental disabilities are about UNEVEN abilities, not no abilities.   Some abilities are at a higher level and others are lower - this is the typical picture with developmental delays.   The key is early education and training.   The brain can compensate for a lot.

There is absolutely NO such thing as 'heightened reaction' to mental illness.   People are always exactly as sick as the physical process affecting their brain, dictates.   There is no middle ground on this.  

 It's exactly as if you had a sprained ankle, you would limp less severely than if you had a broken leg.     A person is just as sick as he is supposed to be based on how the disease affects his brain.   It's directly observable by MRI.   RIght after brain cells in the hearing centers of the brain are destroyed, people start to 'hear voices'.   What kind of hallucinations they have, depends on which areas of the brain are most affected.

 The disease of schizophrenia can be so mild it can't even be diagnosed, or it can be so severe that a person is very disabled (and even more disabled, if no treatment is given).   That has nothing to do with intelligence.   I've met developmentally disabled people who had mild schizophrenia, and those who had severe schizophrenia.

Nor are people with lower intelligence, necessarily having fewer coping skills.   That's also a disgusting premise.

The whole thing is based on ridiculous and groundless assumptions based in prejudice and the idea that the developmentally disabled have 'primitive' brains.   Which is disgusting.

No matter how a human brain is affected by illness, it NEVER becomes 'something different', or a 'primitive' brain.  Even profoundly developmentally disabled people have definite likes and dislikes, even nonverbal, multiple handicapped men with IQ's under 20 will blush when a pretty girl walks by.   No matter what sort of brain disease a person may have, they are still profoundly human, and always will be.

 It's an injured human brain, and the disabilities will be a direct reflection of what was injured and how badly.   All symptoms of schizophrenia are caused by a brain disease.   Depending on what area of the brain is affected, that will be the symptom they get.   There is no 'heightened response'.

Of course, it's necessary to be realistic.  Imagine the difficulty of comforting a child who is severely developmentally disabled, and can't understand what you're saying, that the hallucination isn't real and won't hurt him.  Imagine the difficulty of teaching a young child who is psychotic, blind and developmentally disabled.   Yet skilled therapists do exactly this.

Yet even a profoundly developmentally disabled person with a very low IQ, if they have schizophrenia, can learn coping skills and while it may take more time to teach it by repetition, they do learn those things.   I took care of a young man who had an IQ around 40, and he would give himself 'time outs' to reduce sensory overloading and understood that his medicine 'made the bad guys go away'.   I wish some people with three times his IQ would do that!

Quoting Clairwil:

Quoting stormcris:
Quoting Clairwil:

See the results on page 10 of:

http://www.groups.psychology.org.au/Assets/Files/IQ-and-Mental-Illness-12Aug2010.pdf

Would this suggest that the lower the IQ the more primative the brain thus the heightened reaction to various mental illness because of a lack of coping skills?

I don't know.

I don't have sufficient data to make even a 'better than random' guess.

 

 

SWasson
by Bronze Member on Feb. 23, 2013 at 8:34 AM

It seems to me that the "increased fecundity of siblings" theory would be awfully hard to find evidence of when the siblings in your group have access to and knowledge of contraception.

Clairwil
by Ruby Member on Feb. 23, 2013 at 9:37 AM
Quoting SWasson:

It seems to me that the "increased fecundity of siblings" theory would be awfully hard to find evidence of when the siblings in your group have access to and knowledge of contraception.

It isn't "fecundity" as in "the percentage chance of getting pregnant, per sex act".

It is a wider "fitness to environment" thing.   If the genes in the sibling have the effect of increasing the change of the person surviving childhood (eg disease resistence), getting a high paying job (eg iq), getting married (eg social skills and appearence), etc.  that would all affect the likely number of children.


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