Stem Cells; Yay or nay!?

[shinny]

Randomly digged this up from last year's files for a friend and I actually found it quite interesting as a re-read. It was written as a conclusion for a SAC on the effects of stem cell therapy on the evolution of humans. Any comments/criticisms of my logic and reasoning or the ideas presented? I obviously wouldn't have considered every possible angle on the issue and especially the population genetics and science side of it all, especially since all I had was a high school level knowledge on evolution, as well as some of the points being completely idealistic and would probably take a VERY long time to reach such a state. But basically from what I can see, every bloody second child in like 1000 years will have diabetes or something. That is, unless we haven't fricken blown ourselves up or sucked ourselves into a black hole by then. My bet's on the latter. Anyway here it is; enjoy.

"One major argument is that allowing human embryo stem cell research will pave the way in finding cures for many serious diseases.

The benefits of finding cures using this technology is quite obvious; a reduction in deaths, an improved living standard for many affected people as well as a reduction in costs of on going palliative care. However, in the case of genetic diseases, there are many evolutionary implications of doing so, as it will definitely interrupt the process of natural selection. Stem cell therapy when dealing with genetic diseases may be accompanied by gene therapy as well. From this, it appears that as the genotype of the individual changes as well, then there may be no net effect. However, the genotype of the individual will typically only change in cells that the gene is activated, such as only in pancreatic cells for the treatment of diabetes. This implies that the individual will still have the original defective alleles in his/her gametes, and hence any offspring produced will be able to inherit these alleles.

Considering the above, it is in inevitable that the process of natural selection will be interrupted as natural selection acts on phenotypes rather than genotypes. If stem cell therapy alters an individual's phenotype so that they are not selected against, then this less favourable allele which would normally be selected against will no longer be. Therefore, this less fit allele will continue to be passed on, and possibly increase in frequency. This will ultimately create a situation of what seems to be lowered genetic diversity. Rather, what will actually occur is increased genetic diversity as many unfavourable alleles will be preserved but their phenotypes will be masked by stem cell therapy, creating lowered phenotypic diversity. Yet again, as natural selection occurs against phenotypes, there will be less available phenotypes which can be 'tested' against any new selection pressures. As such, there is a greater chance that a large proportion of the population will be selected against. An example of this could be sickle cell anaemia, which is often viewed as a detrimental trait to carry but in fact provides malaria resistance. If the sickle celled phenotype was completely eliminated by stem cell therapy, any population which then had malaria introduced as a selecting agent would then be widely selected against and may risk widespread death or extinction.

However, despite the above, the majority of the conditions which stem cell therapy can cure are either physical traumas or degenerative diseases. As such, in the case of such conditions, there is not much evolutionary consequence as these conditions cannot be inherited. However, this does reduce the effect of the external and internal environment on the expression of phenotypes as any changes as a result of these environments can seemingly be reversed. This may have an effect on evolution by affecting the outcomes of non-random mating, where individuals select mates based on phenotypes, as is performed in a human society.

Other potentially difficult situations involve gene flow between populations. For example, if stem cell therapy for sickle cell anaemia was available in one well developed country, then the allele would increase in numbers as it would no longer be selected against. However, if a member of this population migrates overseas into another not as well developed country and starts a family here, then the allele would begin to spread. As the cure may not be available here, then the disease would become widespread and ultimately result in a large reduced quality of life for people here."

NOTE: Oh and yes, please don't steal any of this for your own SACs if you've still got one remaining (since yes, this was my last one). Plagiarism is baaaaaaaaad. Feel free to be inspired by it and create your own ideas on the issue though.

[NE2000]

A few points:
- firstly I am of the belief that human evolution has stopped anywayz, or is otherwise progressing very slowly, so I don't think these treatments will really have such an effect on human evolution anyway
- You make the point on sickle cell anaemia, where I thought the heterozygote is essentially phenotypically normal, or displays very few symptoms of sickle cell anaemia and as such doesn't have an impaired function to the extent of people homozygous for the alleles coding for sickle cell anaemia. If that is the case (correct me if I'm wrong) then wouldn't the heterozygotes in the population not need stem cell therapy and will thus maintain their resistance to malaria. The main effect would be that homozygous individuals would survive and yes therefore the s allele for sickle cell anaemia would increased in frequency in the gene pool, but even in developing countries with exposure to malaria, the homozygotes are not selected for.
- your point on gene flow is interesting, because it means that you now have the chance that phenotypically normal parents are actually homozygous recessive and their genotype would normally result in sickle cell anaemia, all their children would have sickle cell anaemia and would need immediate therapy.

I have to do a similar but then again quite different report, but we have a word limit and your conclusion (lol) is pretty much over half that limit.

[shinny]

-My focus was not on so much 'evolution' necessarily in terms of speciation but rather genetic diversity and so on. But still, it COULD have an effect on evolution but its pretty hard to tell, and from what I can see it's pretty unlikely any new species will arise since the Americans will probly just shoot or nuke the first 'freak' they see.
-Point taken. Guess I didn't really consider that in the case of sickle cell anaemia, but I can't really recall many other mutations that humans have had which can be beneficial in certain circumstances. Perhaps another example would have been better.

As for this being a 'conclusion', the rest wasn't an essay like this but rather an article analysis where I just discussed the author's arguments and viewpoints etc. This 'conclusion' was more like a summary essay in itself of the articles and my own evaluation and opinion on the issue in relation to the theory.