Sunday, May 17, 2009

Shouldn't severe stuttering be weeded out?

>> Based on the theory of Evolutions and survival of the fittest...shouldn't severe stutterers be weeded out with Time (thousands of years). So Stuttering might have some evolutionary advantages? Care to speculate? Some people subconsciously choose to stutter. Like self-mutilation (brains of self-mutilators)

 Good question. Here is my answer and I start with some genetics. First of all, the theory of evolution is not about the survival of the fittest but about sexual selection. The gene pool (organism made up of the genes) that is able to spread their genes most effectively via mating will survive. Think of the peacock. The bigger the tail the less fit for survival, but the better for mating because females go for males with bigger tails (god knows why! :-) So it is important to view everything in terms of sexual selection.

Second, only the bad stuff is likely to be selected out. This implies that some features might stay for a very long time in the gene pool, because they do not really hurt the gene pool's chance of reproduction. For example, a gene defect leading to infertility is immediately selected out, but a bigger nose might not because it does not really harm in reproduction. Third, sometimes a genes provokes a bad thing and a good thing. So this big-nose gene might also lead to bigger hands which is an advantage in surviving the environment and thereby increasing chances for sexual reproduction.

Fourth, highly relevant to stuttering, selection takes a long time to select out bad genes. So when you still see the bad genes in the gene pool it might well be that there was not enough time for them to be selected out. In fact, it might be selected out right now, and the proportion of the bad gene in the population might already have decreased. So when you see people stutter, being dyslexic, or genetic heart issues, it might well lead to less reproductive success, but the selection pressure might not be too high or the gene mutation happened not long ago and the people with these conditions might be the remnants of a much bigger population.

Fifth, some conditions cannot be selected out, because it is physically impossible to further improve the organism. Like humans, nature has a limited amount of ressources. Think of health care, you can tak 10 million to improve cancer treatment or 10 million to improve Alzheimer, but you cannot do both at the same time. Same here, some gene might improve things in one part of the brain but make it worse in another. So when conditions are at a very low precentage it might be impossible to further select them out.

Sixth, some conditions like stuttering are not strongly genetic, so it takes much longer to select them out. Also, it is not a single gene most likely, making it even more difficult.

Fifth, some genes only lead to condition in the appropriate environment. So maybe some of our fluent human beings carry the genes but did not develop stuttering or recovered from it. This makes selecting out the genes more complicated.

To summarise, you are making the assumption that the proportion of stutterers has NOT been declining about the last few thousands of years, thereby saying: OK it has been stable and it must be bad, and therefore there must be a counterforce. I would argue that the most likely scenario is that the proportion of stuttering is still declining, being selected out, and that stuttering might be less critical for reproduction sucess in our ancestors where hunting skills were much more important. And I also believe that nature might well not be able to optimize the brain much more so selecting out might take a very long time. Of course, it might be that some stuttering genes might give some benefit to the carrier; maybe it protects against a disease at the expense of stuttering. And again, stuttering is not strongly genetic, so selection will take longer.


Anonymous said...

You ask, "shouldn't severe stutterers be weeded out ..."

Assuming that there is a specific stuttering gene - then the only way stuttering can eventually be weeded out is if all stutterers never have sex and procreate. But the weeding out might take a lot of time because a person who carries this fictitious stuttering gene might not have a stutter, so he/she might pass on the gene to, say, 2 children - one of whom ends up stuttering, and the other is fluent. Genes are not the only things that have impact - there are also environmental factors.

There's also the very strong possibility that the hypothetical gene might have nothing whatsoever to do with speech. As we know, one gene might affect another gene which affects another gene etc. So it might affect speech in an indirect way.

But it's all hypothetical because the researchers working on stuttering are totally incompetent. Unless there is some improvement in the quality of researchers, we may never know.

CJ said...

Hi Anon, can you say more about:

"the researchers working on stuttering are totally incompetent...."

Everyone is incompetent....I do agree that a lot of speech therapist are incompetent (first hand experience). So there is NO hope.

Anonymous said...

Developmental Stuttering may persist because most who stutter recover before adulthood. The genes pass on via those who currently stutter and those who's stuttering already had resolved.

ac said...

Is it possible that even if no stutters were to ever have children, the genes that carry the tendency would be passed on by their non-stuttering or recovered siblings? Maybe if you analyse this model the particular mutation will die out over enough time, but it seems plausible that there is a steady state solution.

Kanstantsin said...

The major transmitters of stuttering genes might be women. One can imagine that many of them are carrying stuttering genes, but these genes do not manifest themselve phenotipically as stuttering in female body. That's why 3-4 times less women are suttering than men.

Anonymous said...

Tom, is this true? (What Kanstantsin said??)

Or not true? (Not as simple as it seems....)

Kanstantsin said...

This is just my hypothesis :)

Anyway, nobody knows so far any genes associated with stuttering.