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Human Genome Degeneration

  1. Sep 27, 2016 #1

    micromass

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    Hello everybody,

    I encountered this weird theory that I don't really believe to be valid. But it sounds pretty plausible, so I'm going to let you guys tell me whether it is correct or not.

    Anyway, the link is here: http://www.onelife.com/evolve/degen.html (warning: possible crackpot link)

    The idea is simple: modern medicine allows many people to live and reproduce that wouldn't have otherwise. This means that certain bad mutations of DNA are not selected against anymore. This means that the human DNA degenerates leading eventually to the extinction of humans in the coming few hundred years.

    Apparently this idea is shared by a Cornell professor (who also happens to be a creationist....): http://thetruthwins.com/archives/th...ally-lead-to-the-total-extinction-of-humanity

    So a few questions:
    1) Is this basically correct?
    2) Are there any peer-reviewed papers on this material?
    3) How do the modern advances in medicine affect the mechanism of natural selection? It definitely didn't stop natural selection, but did it slow it down? Or did it change?
    4) Can anybody name an example of evolution by natural selections in humans in the last 100 years?
    5) Is it true that the human being is getting "weaker" genetically due to modern medicine?
    6) Is it true that humans have more genetic diseases than other species?

    Thanks you!
     
    Last edited: Sep 27, 2016
  2. jcsd
  3. Sep 27, 2016 #2

    Bystander

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    Questions 1, 2, 3: Who knows? 1) probably not. 2) none that I'm aware. 3) too early to say, since it takes seevvveeeerrrrraaaaaallllllll generations to see any effect.
    Question 4: 1002 good enough? Sickle cell anemia.
    Questions 5, 6: Who knows? Probably not, and tough to say since there is no real data base for "other" species.
     
  4. Sep 27, 2016 #3

    jim mcnamara

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    It is crackpot fodder. @Bystander pretty well nailed it.
     
  5. Sep 27, 2016 #4

    Drakkith

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    My understanding:

    1. No. It's BS. The human race is not going to go extinct in the near or moderate future because of genome problems. In the absence of natural selection forces, both "bad" and "good" mutations can propagate throughout the species thanks to genetic drift, so there isn't even a way to predict what will happen as far as I know. Also, note that if we did begin to have issues with our genome, those individuals with fewer problems would, at some point, outnumber those with more problems. These individuals would pass on their genes more often than the others. Thus there should be a self-correcting force at some point.

    The article makes multiple, severe errors when it comes to evolution. For one, their own argument that our species will go extinct goes against their claim that organisms will evolve to match their environment. If this is our environment, then we will evolve to match it, not go extinct. I mean, that's pretty much the red flag that they have no idea what they're talking about when they defeat their own argument!

    2. No idea.

    3. Not sure. It's certainly true that modern medicine (and other areas of science and technology) have drastically changed the environment that humans live in. The average individual is much more likely to survive thanks to the eradication/reduction in epidemic diseases and diseases of childhood along with their access to medical resources in the event they do get sick. However, we've also changed many of these diseases. So-called "superbugs" are evolving that are resistant to nearly all antibiotics, so we may be facing the resurgence of killer diseases.

    4. 100 years is a very short time for evolution to act on our species. That's only around 3-5 generations. Any evolutionary changes would be small and would not be widespread yet. We certainly aren't going to go extinct in a few hundred years. That's pure nonsense.

    5. No.

    6. Unknown. We've obviously studied our own genetic diseases much more extensively than other species, so it's hard to do a comparison. It's certainly true that many individuals with genetic diseases are able to survive and pass on their genes thanks to modern medicine, but it's also true that genetic testing can counteract this.
     
  6. Sep 27, 2016 #5

    Ygggdrasil

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    Whether a mutation is deleterious to fitness depends a lot on the environment. The mutation that causes sickle cell anemia helps protect against malaria. Genes that make humans crave calorie rich foods that helped our hunter-gatherer ancestors are likely maladaptive in the developed world where obesity is a bigger problem than malnutrition.

    Thus, the argument's whole premise is flawed. The author is arguing that modern medicine has increased the genetic diversity of the human race by allowing the existence of traits that might otherwise have disappeared through natural selection. However, genetic diversity is a species' greatest defense against extinction, providing the basis for a population to adapt to changes to their environment. What if some deleterious mutation that seems to impair some individuals' ability to function in some context provides immunity against the next worldwide pandemic? (Of course, modern medicine, not genetic diversity, is likely what will protect humanity against extinction in the face of a pandemic disease). Genetic diversity is a strength not a weakness.

    The premise also misunderstands evolution. Natural selection is only one mechanism by which evolution can occur. Random genetic drift plays as big, if not a bigger, role in evolution as selection. Indeed, natural selection in humans is likely occurring at a very low rate, but this is because the rate at which new mutations become fixed in a population depends both on the strength of selection as well as the population size. While modern medicine has likely decreased the strength of negative selection against certain traits, the large size of the human population serves as a much greater barrier to the fixation of new traits. In such a large population, the effects of genetic drift will almost always be larger than the effects of natural selection except in very extreme circumstances (e.g. pandemic disease). Because modern medicine is responsible for the large size of the human population (another good protection against extinction), the author is correct that modern medicine has decreased the rate of natural selection, but for completely wrong reasons.

    On the issue of examples of recent human evolution, here's an article discussing some examples from the thousands to tens of thousands years ago. Finding convincing examples in the past hundreds of years is likely very difficult given human generation times.

    Finally, if one is worried about extinction, there are much greater problems to worry about (climate change, nuclear weapons, etc.) than human genetics.
     
  7. Sep 27, 2016 #6

    russ_watters

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    The idea makes no logical sense:
    [Edit: misread]
    How are issues that don't affect reproduction (because of modern medicine) going to affect reproduction in the future?

    I'm more worried about the negative evolutionary pressures (and related social pressures) of modern society.
     
  8. Sep 27, 2016 #7

    micromass

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    Look at it like this. Assume a child is born with a serious defect, like Down syndrome or Spina Bifida or without legs. It is reasonable to accept that before modern medicine, these people would have a very hard time surviving until adulthood. Thus these people would have a lot less chance to reproduce because they wouldn't survive. With modern medicine, we are letting a lot more people survive that wouldn't otherwise. I am wondering how this would affect our evolution as a species.
     
  9. Sep 27, 2016 #8

    micromass

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    Thank you very much for your very detailed answer! Especially thank you for providing so many interesting references. This was very very illuminating and exactly what I was looking for.

    Also thanks for Bystand, Jim Mcnamara and Drakkith!
     
  10. Sep 27, 2016 #9

    russ_watters

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    I'm with you to a point: those issues/people are more survivable today, but I doubt they will ever be equally survivable and equally as likely to reproduce as those without such issues. So while they may slow the filtering, I don't see how they could invert it or lead to extinction.

    I'm much more worried about the very real and significant evolutionary/social pressure against intelligence and related qualities that exist now.
     
  11. Sep 27, 2016 #10

    Drakkith

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    Can you elaborate on this? It's not something I've heard before.
     
  12. Sep 27, 2016 #11

    Bystander

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  13. Sep 27, 2016 #12

    russ_watters

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    I'm referring to this phenomena:
    https://en.wikipedia.org/wiki/Fertility_and_intelligence

    It is a relatively recent phenomena, which makes the manifestation of actual evolution weak and difficult to measure, and the biological vs social components are tough to separate, but the difference in birth rates with respect to intelligence related measures is very strong.
     
  14. Sep 27, 2016 #13

    russ_watters

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    Not sarcasm, unfortunately.
     
    Last edited: Sep 27, 2016
  15. Sep 27, 2016 #14

    Ygggdrasil

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    I haven't read the details of the studies described, but here's an article discussing whether the Idiocracy hypothesis is backed up by science:
    https://www.bloomberg.com/view/articles/2016-06-14/the-idiocracy-may-be-here-but-it-isn-t-hereditary

    They don't see any genetic changes that would suggest russ's worries are correct, but one would probably not expect to see genetic changes on the timescales measured. Of course, cultural and social changes can be just as important and these were not measured in the study.
     
    Last edited: Sep 27, 2016
  16. Sep 27, 2016 #15

    Bystander

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    https://en.wikipedia.org/wiki/The_Bell_Curve
    Can't say The Bell Curve, been in my library since publication, lends any sort of veracity to the Wiki argument cited (or that any sociological Wiki article/argument has a whole lot of significance). This seems to bring the discussion "full circle." i.e., an inquiry based on "hearsay?"
     
  17. Sep 28, 2016 #16

    Bystander

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    Rephrasing: "stupidity" may run in families, but it's not genetic.
     
  18. Sep 29, 2016 #17
    what do you guys think is the cause of mutation
     
  19. Sep 29, 2016 #18

    Drakkith

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    Well, a mutation is simply a change in a nucleotide of DNA. There are many causes of this. Ionizing radiation (UV, x-rays, gamma rays, etc), chemicals, oxidizing agents from normal cellular processes, viruses, and more.
     
  20. Sep 30, 2016 #19

    BillTre

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    Natural selection continues on. There may or may not be a change in the rate or in what aspect of humans is changing as a result of selection, but there will be selection, even if it is only stabilizing (selection to maintain the current situation).

    Artificial selection (under the control of humans) may also affect humans, depending on how you think about it.
    It has been said that human behavior was selected to more "mild" as a result of the development of complex humans societies where a lot of people are living together and less violence is more adaptive.
    Would this be artificial or natural?
    Would this be the domestication of humans?


    Perhaps.


    It would actually be not just a change in a nucleotide, but a change in the nucleotide sequence. This would include the removal, addition or moving of bits of sequence (deletions, insertions, and translocations respectively), in addition to a change in a base.
     
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