Far from ignoring the point, this IS the point. Since the defective genes are passed on we have a state of increasing genetic disease in the population.
Only if there's no selection is there a situation of increasing genetic defects in a population, which may be the precise case for homo sapiens. If that's your point, then I agree with you. One of the dangers the human race poses for its own survival is that our ability to develop medical treatments for genetic diseases allows people with genetic defects, who in earlier times would have died young, to produce offspring.
Definitely, and this has to be sorted out from defects which are simply passed on "in the wild" because they are not selected out because they do not affect reproduction, which is the situation I think is being discussed here. However, it may need to be rethought in the case of diabetes, which Ramoss brought up in
Message 148. The gene may be passed on, in fact it seems to be associated with fewer miscarriages according to him, but if this gene must pair with a similar gene in order to produce the disease, childhood diabetes, which is fatal without the medical intervention we now take for granted, then all we have is proliferating genes in the population and not the disease itself. BUT this very situation increases the chances of the combination that produces the disease.
And what is a "gene for diabetes" anyway? I have trouble thinking of a normal function, a gene, in terms of producing a disease. Is a "gene for diabetes" a gene mutated from a gene that regulates blood sugar in a beneficial way perhaps, or something like that? Isn't there some way to describe it in terms of a genetic defect, or is it simply that the way it sprawls there along the DNA chain it looks and acts for all the world like any other gene so you can't make such a distinction?
One extremem example that comes to mind is cystic fibrosis. Individuals with this genetic defect used to die young, but modern medicine now allows many to live into their 40's. Because cystic fibrosis is an extreme example where every victim is intimately familiar with the consequences of the disease, victims probably rarely pass this gene on. They either choose not to have children, or they use genetic screening to check for the presence of two defective copies of the CFTR gene before birth and terminate the pregnancy.
For the sake of this discussion it would be good to confine it to mutations that produce diseases that don't in themselves prevent reproduction.
Are all genetic diseases a matter of the combining of two of the same defective genes?
But other less severe genetic defects, like color blindness, are probably passed on all the time. In modern societies the survival cost of color blindness is minimal, but in prehistoric times it was probably much more important. For instance, those with color blindness often have much greater difficulty seeing in the dark.
But it seems to me we can define this as a defect whether or not it interferes with survival.
Actually, there are some questions raised about genetic transmission in this case, though as a side issue. Color blindness is predominantly passed on through males, but I inherited a very mild case of it -- undetectable except on very refined tests -- apparently from my father who had severe red-green color blindness (he distinguished the red signal light from the green one by degree of brightness and position above or below on the pole). I have trouble distinguishing a light pastel shade of yellow-green from the same light shade of orange or peach. I identify them easily in contrast with a stronger color, but they both blur to beige in each other's company. But how does a mild case of anything, or a degree of anything, get passed on? You'd think that you either have two genes for something, which would then be overt rather than nearly undetectable, or you don't have the disease at all. I'm sure there's an answer to this, I just don't happen to have run across it.
Visual acuity and focussing ability also has a genetic component. Darwin observed in Patagonia that the natives all had far better vision than the Europeans. In a civilization without eyeglasses, the genetic ability to produce good eyesight would be well maintained.
Well, maybe, but how would you know for sure that this is a case of natural selection? That would imply that any who were born less visually acute would fail to reproduce because of lack of that acuity, doesn't it? Is this visual acuity the case for all native tribes everywhere? It may just be that the progenitors of the Patagonians happened to have good genes for vision, "selected" purely circumstantially by migration rather than adaptability. (My colorblind father, by the way, also had the most amazing long-distance vision. Could see things miles away, miles down a stretch of endless Nevada highway for instance).
So I think you have a good point for homo sapiens, but we're increasing the defects in our gene pool through articial rather than natural means, usually medically related means. We even do the same thing for our pets. For instance, I believe german shepherds have a genetic defect that causes hip problems, but we treat the hip problems and allow the dogs to reproduce. Of course, it was humans who bred german and shepherds and all other dogs from wolves, anyway, so perhaps this is too artificial an example. But you probably get the idea.
Yes, but we should be trying to avoid these examples for the sake of this discussion and focus only on defects that are passed on without medical intervention.
In the wild, medical means of alleviating the effects of genetic defects are not available, and genetic defects are filtered out, meaning the affected individuals do not survive to produce, or if they do, they produce fewer offspring than unaffected individuals.
Fewer offspring might be relevant here. The examples that have so far come up are Ramoss' example of diabetes and DrJones' example of keratoconus which he says in
Message 154 slowly leads to blindness.
And what I am saying is that this means that evolution is really impossible, since not only does speciation lead to decreased genetic variability, but the passing on of diseases in the population leads to overall lack of vigor that all by itself tends to extinction rather than to anything that could produce a healthy species as evolution implies must happen.
You say that evolution is impossible, and I grant that your misunderstanding of evolution is impossible. This is representative of too deep a misunderstanding to take the time to correct.
There is no misunderstanding. I learned the rap about reproduction and selection and survivability etc. back in high school. I am simply pondering some implications of genetic diseases in the last few posts.
I know that's a copout, I'm criticizing without providing the proper counterpoint, but I am pressed for time right now. Please give me a pass on this for now and I'll try to come back to it later.
OK but it's more than a copout, it's "poisoning the well," that is, making sure that you establish firmly in the reader's mind that Faith doesn't know what she's talking about although you haven't proved it.
So far in this discussion there have been no examples of these, only examples of "neutral" mutations that cause disease.
I don't think we should let any formal definitions of "neutral mutations" get in the way of understanding. Whatever those definitions might be, I think your approach makes more sense. Describing as neutral a genetic defect that adversely affects the ability of an organism to produce offspring does not make any sense to us laypeople.
But I wasn't talking about inability to produce offspring. I was talking about the proliferation of disease in the population, or general weakness of one sort or another that would NOT affect ability to reproduce -- apart from medical intervention. I think it very likely that overall the entire human population has generally far less strength of various kinds than was the case a few millennia ago.
Dr. Jones described his keratoconus as a "neutral" mutation. I think there must be many examples of this sort of thing but so far only a couple have come up. Schraf added her example after your post. Simply carrying a defective gene doesn't interfere with reproduction or quality of life in most cases apparently, but if it combines with another of same the effect may be lethal to the offspring, or maybe it won't be, merely cause some awful condition that kills the person slowly after reproductive age, or just produces pain and suffering over a long life.
Evolution seems to assume that genetic defects just happen to crop up from time to time at a probably predictable rate -- always and forever, on the uniformitarian principle -- but that we can count on the various selection processes to weed them out. Seems to me that as long as some don't interfere with reproduction that over time they would increase in the population and make for a rather sickly bunch even if they could survive because of compensating strengths or an accommodating environment. Ultimately such a trend WOULD tend to extinction though, which is simply an extreme selection process after all.
I'm addressing a supposed "neutral" mutation, two of them, both causing disease. The supposed "good" mutations are pretty much a wishful fantasy so far.
Haven't examples of good mutations been provided for you in the past? Anyway, one common type of good mutation is caused by gene duplication. Let's say there's a gene that provides a beneficial protein, say a protein involved in muscle endurance. Now there's a mutation that duplicates this gene, and so muscle cells suddenly start producing twice as much of this muscle endurance protein. That's an example of a beneficial mutation.
I have had trouble following some discussions of supposed good mutations, but in this case you are offering, why is it you can only offer a hypothetical? Why do you have to give a "Let's say..." instead of a known fact? The defective genes and their diseases are facts. Diabetes is a fact. Keratoconus is a fact. (Actually, I just looked it up, and contrary to what DrJones said, the
wiki article says it does not lead to blindness.) Cystic fibrosis is a fact. These genetic diseases all are facts, not hypotheses. I've seen long lists of them. Maybe I should look up such a list. {edit: Done:
List of genetic diseases and lots of discussion.}
Anyway, I need a factual example of a "good" mutation along the same lines -- and to know why it's considered to be a "mutation" too, rather than just a normal genetic option. And please, no bacteria, only sexually reproducing examples.
Any particular gene can experience many different types of mutation, from simple nucleotide replacement to complete inversion to complete removal. While most potential genetic mutations are either harmful or neutral, some mutations are improvements, and the probability that these mutations will happen is not zero. Hence, given time they are inevitable, and to the extent that they provide an advantage they will propagate throughout a population.
Again, this is merely hypothetical. But as you asked, I will grant you time to come up with some factual examples. AND again, please, a consideration of what makes these "mutations" rather than normal genetic options that show up in the normal course of reproduction.
Edited by Faith, : No reason given.
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