Why doesn't natural selection eliminate genetic diseases?
I can think of a few special cases that would explain why a genetic defect is able to persist. I will list them, along with some speculations, to move the discussion forward, but I would like to know if there are explanations for other cases.
The gene that causes sickle cell anemia does so when there are two copies of the gene, but if there is just one, which is much more common, it provides protection against malaria. Are there other genetic defects that follow the same pattern of causing problems if there are two copies but providing protection if there is just one?
Another possibility would be that a disease is of comparatively recent origin. Maybe there are certain mutations that occur relatively often, allowing the perpetuation of the defect.
There is the possibility that what we call a disease was of benefit at an earlier time in our history. There was a recent post that said that the symptoms of ADHD are beneficial for hunter gatherers. What about other mental disorders with a genetic component like depression and schizophrenia?
There are some genetic diseases that do not occur until comparatively late in life. These diseases may not have occurred with any frequency until fairly recently, because people are living longer lives, or maybe after a person successfully raises a family the genetic defect does not have much of an evolutionary impact.
Are there any other explanations? Why, for example, do people get hereditary diabetes or hemophilia?
Observing members:
0
Composing members:
0
11 Answers
I am not sure about a lot of genetic diseases but, some persist because they don’t effect all people who have it the same. For example, Bruton’s Agammaglobulinemia, which is a genetic disorder that runs in my family, limits the body’s immunoglobulins. This means, essentially, that the person with the disorder has no immune system. However, only men in the family show this symptom. And the women are the ones that pass it on. To illustrate: let’s say I am a carrier (I have been tested and am not). I had a 50% chance of getting this from my mom (it is a mutated gene). I also have a 50% chance of passing it on to my children. If it is a boy who has it, he will be born with no immune system. If it is a girl, she will be normal, except that she will always run the risk of having a son with no immune system.
Hope that wasn’t too confusing…
In a nutshell…this persists b/c it is rare enough that if it skips a few generations w/o notice (very possible) then the family doesn’t even realize they have it. Also, b/c it manifests differently based on sex, and has a 50% chance of appearing, it isn’t easily scratched out.
Perhaps if our population wasn’t quite as big, it would matter more. But with modern medicine, the idea that even sick people should be taken care of (and then they grow up to have kids of their own), we’ve really mostly eliminated natural selection from working in our species except in the grossest of circumstances. Hereditary diabetes would have been a disaster back in the day, but now with things like insulin and knowledge, it’s no longer as big of a problem, and diabetics have lives…and children.
I would say its because we reproduce before the condition has a chance to kill us. and thus it gets passed on. natural selection only really works if it kills you before you reproduce. otherwise the trait lives on.
as many conditions such as heart disease dont kick in until later in life, chances are the condition did not prevent you from reproducing.
as for ones that kill you early on, i would say it is probably just down to bad mutations. some are successful some are not.
add to that, the fact that we have only had modern medicine for a very short time. maybe a couple hundred years at best. and you cant really say, we have no idea just how new some of these conditions really are. given that evolution happens so slowly, i dont think there really is much we could say about just why we have the conditions we do. i think that needs more time. then again, im no expert.
Because we have reached a point where natural selection no longer has any effect on us. Our medical technology keeps people alive that normally wouldn’t be able to. Natural selection now is “are we able to cure that?”
Oh yeah – things like rampant diabetes? It comes along with a processed, Western diet – so it’s pretty recent in the grand scheme. When a society gets rich enough to afford processed and convenience foods and white flour, sugar and too much meat, they get just as fat and diabetic as Americans. I’ve also read about people who got better (diabetes controlled to the point of almost nonexistence, health returned) when they went back to their native diets.
And does the very different environment we have made for ourselves cause some of the bad, bad genetic flaws? I think many of the very damaged babies would have died even 30 years ago so that would be natural selection.
Many genetic diseases don’t kill people before they have sex.
As others have mentioned if you ca make it to the reproductive years you can pass along the “bad” genes. Also, if you are heterozygous for a disease, and the disease only shows itself if you have genes from both parents, then you can pass it along.
We as human’s have ceased natural selection in our kind. If we still lived not unlike the animals do, genetic disease would definitely have changed over time. Since as a society we preserve every human life, we can no longer go through with Natural Selection. It is very UnNatural selection ha ha.
For humans, selection is now based on other factors, like appearance and social/career abilities. We will end up as Eloi and Morlocks.
Nowadays natural selection only weeds out those who are too stupid to survive – people with no common sense or sense of self-preservation. As far as medical issues and genetic flaws, we can keep anyone alive, no matter how messed up they are.
Answer this question 
This question is in the General Section. Responses must be helpful and on-topic.
Composing members:
0
