Peter Law


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Why doesn't natural selection eradicate disease ?

Let's take a disease; eg. TB. Those who have it die younger, & are less successful at reproducing. Given time shouldn't TB be eradicated by natural selection? Ditto for all disease. Why is this not happening ?

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    Dec 15 2012: Because not many diseases are viable for your scenario.
    Most diseases fall under the categories of:

    -Infectious > Which is not really relevant to this argument as it can be passed on despite age.

    -Non-communicable > Not really relevant to this argument because most are subject to lifestyle and mutations (for example), often over long periods of time and not necessarily hereditary.

    -Hereditary > Most of which may not have any early on-set of symptoms or even exist until later on in life.

    So its hard to see exactly how many diseases could be eradicated through natural selection on its own in this process.

    Its quite likely that there was a point in history where the effects of disease would become immediately obvious, thus that person could be isolated/killed which eradiates the disease. Ofcourse, don't forget that disease itself is also subject to evolution in order to try and survive..
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      Dec 16 2012: Is your conclusion that infectious, non-communicable, and hereditary diseases are exempt from natural selection of beneficial mutations from a common ancestor over eons of time? If so, please share your supporting premises for such a conclusion. Thank you!
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        Dec 16 2012: I didn't say any of that. I infact implied the *exact opposite* in the last 3 lines..

        Edit: @ Edward Long. (As I cant seem to reply to your recent response directly).
        Well what I mean is that diseases would not be killed off in the scenario of natural selection given by the author (where the disease solely effects those prior to pre-reproductive ages), because for what ever reason, the diseases don't often solely focus on that group or the group in its entirety.

        Because of this, they are not bound by that specific scenario of natural selection
        hope that helps.
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          Dec 16 2012: Just clarifying, Mr. Belevmont, no hostility intended. I know what you implied in the last three lines. My question to you is about what you stated outright in the first eight lines. Why do you state that the three categories of disease you mention are not "viable for your scenario"? It seems like you are saying they are impervious to the mechanisms employed by the currently accepted theory of evolution. I do not understand your point. Thank you!
  • Dec 21 2012: I believe it is; take the "childhood" diseases of measles and chicken pox. Western Europeans developed a form of immunity to these diseases in that we can catch them in childhood, and not suffer too seriously from them. (I did; in fact, my parents exposed me to a kid who had measles so I would get them while young, and not have a worse case when I grew older. This was the "norm" back in the '50's.) However, Native Americans hadn't had the long history of exposure to these illnesses, and measles killed them by the thousands.
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      Dec 22 2012: We are of the same generation, we visited each other to catch measles, mumps, & chickenpox. We have an excellent immune system which is very effective at keeping us well, normally.

      My point is better seen from a longer perspective. Evolution is credited with producing a wide variety of creatures from simple beginnings. In comparison with evolving a 3D colour set of eyes, eradicating disease is a much more basic prospect. Creatures who have disease are obviously not as effective reproducers as healthy creatures. Given the option of evolving colour vision (as against b/w), and eradicating disease, I would have thought eradicating disease would be the natural selected option.
      The same thing goes for longevity, or immortality. Why wouldn't natural selection favour long, healthy, life; which would obviously be advantageous? Life expectation is really pretty dire after all these millions of years of supposed advancement.

      • Dec 22 2012: Immortal organisms, do exist: all single cell life is immortal and so are some primitive multi-cellular organisms. More complex organisms with larger numbers of cell types tend to develop cancer if they keep on living.
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    Lejan .

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    Dec 17 2012: For the same reason, that mankind did not extinct by its poor and risky design combination of its gullet and respiratory tract. Not all diseases are a separate 'life-form', they are malfunctions within the biological complexity of a species and not all of those are encoded within our DNA. And even those who are encoded may not always be lethal and early enough to stop 'their' reproduction.

    By the way, what makes you think that TB is causing any lower 'success rate' in reproduction? Don't you know that TB is an infectious disease an can therefore happen once one has successfully reproduced already? This disease is actually based on a separate life-form, which is bypassing natural selection due to its infectious character. Any deadly virus or bacteria has to be infectious, as otherwise they would end their own existence in their very first 'victims'.

    Genetically induced infertility would be eradicated by natural selection, and this happens ever since.

    Other genetically induced diseases may not exist anymore if their impact on those individuals was radical enough to prevent their 'genetic information' to be passed on to following generations.

    Those 'external' diseases we know today are those who finally 'made' it in their 'host' species, and the worldwide battle against Smallpox was a successful example, that this infectious bypassing strategy against natural selection was eradicated by modern medicine. Since 1977, small pocks did not recover from this 'vaccination of mass destruction' and has probably become extinct as a human disease.

    Natural mutation and selection is one of the major forces for viruses and bacteria to constantly adapt to constantly changing defense strategies of any host species, as this is what evolution is about, if one is willing to accept this concept of life over religious believes on its creation and further development.
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    Dec 16 2012: Because natural selection applies to diseases as well. Probably quicker as the lifespan is so much shorter. Now we have super TB. Natural selection does not just humans or mammals or insects or whatever .
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    Dec 16 2012: it does. but then new diseases come up. that's how it works.
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      Dec 16 2012: They reckon that arthritis has been around for 150 million years. Surely that's time enough for natural selection to eradicate it ?
      Do you know of any disease that has been eradicated by evolution ?

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        Dec 16 2012: Peter,
        There are over 100 diffeerent forms of arthritis, including "An undifferentiated arthritis, which does not fit into well-known clinical disease categories". It appears that arthritis is evolving too!
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        Dec 16 2012: surely not sure. crocodiles are around for 150 million years too. sometimes evolution comes up with something that survives for that long. arthritis is a good candidate for that, since it does not affect reproduction, having its usual onset in the late adulthood.

        i don't know a specific disease that was eradicated, since we study diseases for like 10000 years, a blink of an eye for evolution. however, there are lot of structures in every organism that developed by evolution, and aimed to eliminate diseases. for example there are a lot of tumor suppression procedures in our own cells. and simple organisms often have hard-coded antigens, for example RNA sequences that bind to one specific virus DNA to disable it. clearly, the virus DNA had to be existed first, and the organism developed this specific defense later.
      • Dec 17 2012: Arthritis happens after reproductive age. By definition natural selection acts only on traits that have something to do with reproduction.

        Also, natural selection is not just about us. It is the result of the way things work. It has no favourites. Why should it care what you want? It's not a god. Measles is viral There are so many particles of virus that they mutate into enormous variety. That variety means that virus can evolve very quickly.

        I suspect that you have no idea what you are talking about when you say "natural selection."
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        Dec 17 2012: Seems to be a simplistic view which I guess is leading to a false dichotomy. Perhaps you think the existence of disease is evidence that evolution is false, which is incorrect.

        Im not sure why you think evolution would lead to the eradication of disease. Suggest natural selection may lead to populations becoming more resistant to certain forms of disease. As stated bacteria may evolve too.

        I note we have evolved to have immune systems.

        Evolution doesn't lead to perfect beings. Just more adapted populations.
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        Dec 17 2012: 'Do you know of any disease that has been eradicated by evolution ?'

        As viruses and bacteria are to small for petrification, how could we ever tell?

        And arthritis is nothing what stops any species from reproduction, so why should this disease be eradicated by natural selection? Just being 'unpleasant' isn't enough 'selective pressure' for it to vanish.
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    Dec 16 2012: Diseases aren't static; they are also subject to natural selection, and that is why they have not been eradicated. TB in particular lies dormant after one is infected with it, preventing detection. Like all bacterial infections, it is contagious to boot, so the death of the host doesn't eliminate its presence.
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      Dec 16 2012: I agree Kitty Hawk. It seems apparent with recent scientific studies, that diseases, bacterial infections, viruses, and fungal infections are evolving as well. As you say, the death of the host doesn't eliminate the presence of diseases, bacterial or fungal infections or viruses. They simply evolve/mutate. We see this very clearly with infections, in relationship to antibiotics and the ability of infections to become resistant to antibiotics.
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    Dec 18 2012: To me, The Food Chain is a very big design flaw. Creatures should not have to eat creatures. There are so many genetic permutations for virus and bacteria, that humanity will need a lot less malls and a lot more labs.

    Thank you for the question:)
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    Dec 18 2012: Natural selection has not work since man thought they could play god
  • Dec 17 2012: Choice. Diet, exercise, environment, governmental policies, evil, and etc. What we allow affects. Many diseases are brought on by poor choices. Thus, a perfect schematic doesn't necessarily preclude outcome in humanities case. Underlying factors matter.
  • Dec 16 2012: As other people here have said before: disease causing organisms evolve too and they evolve faster than animals and plants, fortunately animals and plants have immune systems that can adapt during a lifetime, without requiring genetic mutation. Anyway, diseases are usually categorized by symptoms, not their causes, so a disease may continue to exist if humans become immune to one of the organisms that can cause the disease, but not all. Other factors are that many diseases are caused by the environment and diet, so no amount of immunity against bacteria and viruses will help and there are also many diseases that are caused by bacteria and/or viruses but exploit essential mechanisms that are shared by a large group of organisms (say mammals, vertebrates, the animal kingdom or even all multicellular life) and are thus very hard or even impossible for evolution to find a solution for, especially if a change to such a mechanism kills more organisms than the disease does.
  • Dan F

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    Dec 16 2012: As noted, natural selection is in play with disease causing organisms and their short regeneration period gives them advantages of adaptability and niche expansion over the adaptability of the hosts.

    Natural selection of humans has provided us an indirect advantage in fighting disease which is unique to humans. It has enable us to develop a parallel cultural evolution which has expanded our ability to fight disease beyond natural selection. Individuals among us have discovered and apply numerous ways to better survive certain diseases by better hygiene, wonder drugs, immunizations etc., In spite this incredible knowledge and acquired advantage, disease is far from eradicated and that speaks volumes as to the tenacious nature of natural selection in the microscopic world of disease producing organisms characterized by extremely short life cycles.
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    Dec 16 2012: From an evolutionary stand point you don't need to eradicate a disease you just have to cope with it long enough to allow reproduction. Today very few people die from diseases that occur before they have reproduced and of those that do the diseases are often a result of lifestyle choices where your free will puts you at risk.
    • Dec 17 2012: "From an evolutionary stand point you don't need to eradicate a disease you just have to cope with it long enough to allow reproduction."

      This is not entirely true: unless a child lives in a welfare state it will have a better chance at survival and a successful life (attracting the most desirable partners) if its grandparents are alive throughout its childhood.
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        Dec 17 2012: On an evolutionary time scale most of human existence has occurred at times when the average age at death was in the 40s so the presence of grandparents has only become common on a time scale too short to influence the gene pool greatly plus up until the last 10,000 years or so all states were welfare states. We were all socialists before agriculture. I do accept your point in the modern world though.;)
        • Dec 18 2012: Averages say nothing about the individual: the average life expectancy was 40, but that was heavily skewed by infant mortality. If you survived your childhood it was not uncommon to live into your 50s or 60s. The evolution of the menopause shows that a non-negligible percentage of prehistoric humans lived quite a lot longer than 40 years.
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        Dec 18 2012: Agreed but if tribal societies of recent times are any indication of the past then the tribal elders functioned as grand parents for the whole tribe so it wasn't such a big thing if your actual grandparents weren't around. This is based on Australian Aboriginal tribal life which is considered to have been fairly consistant in culture for 30-40 thousand years.
  • Dec 16 2012: Natural selection is a mindless process that does not favour bacteria or humans over the other.
    The opportunity for change occurs during reproduction where random mutations in DNA can result in changes to the function of the organism.
    Given that bacteria reproduce in the range of hours to days and humans in the range of 20 years or so, it would seem that the little guys will always have the upper hand.
    That doesn't mean that diseases always get worse. Take Syphilis for example. When the first big plague went through europe in 1494 (I proscribe to the Columbian theory) the attack was so bad that sores would cover almost all of the body, flesh would fall from the victims face and death would mercifully follow closely behind.
    Later on it settled down to the disease that we know and love today.
    Isn't the universe wonderful
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    Dec 16 2012: I take on board the comments below. However the process of evolution is credited with producing 3D colour vision, intricate body systems, subtle differences between male & female, & millions of traits in millions of plants & animals. It seems to me that the eradication of disease should be a fairly basic & straightforward result of natural selection. Defeating measles should be a walk in the park after creating a butterfly from a melted caterpillar. Maybe it's just me ?

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      Dec 16 2012: Peter,
      As you say, the process of evolution creates all kinds of changes. What leads you to believe that diseases should be eradicated, while every other system is evolving, as you insightfully point out?
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      Dec 16 2012: "It seems to me that the eradication of disease should be a fairly basic & straightforward result of natural selection. "
      Sure, if the disease wasn't evolving too, often at a faster rate than we are (given the span of bacterial/viral genration spans).

      'Defeating measles should be a walk in the park'
      Measles rarely kills the people who contact it and I would assume that most go on to reproduce as the illness only exists in the host for a short period of time with little/no effects afterwards.
      The only immediate mechanism of the body would be to expel the virus or attempt to kill it, which is what happens, only the virus spreads at a rate faster than our bodies can do that
      and ofcourse the strains mutate aswell.

      'Maybe it's just me ?'
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      Dec 17 2012: 'Defeating measles should be a walk in the park ...'

      It seems you confuse 'evolution' with 'perfection' here and it may help your understanding if you try to picture evolution more like a constant race and battle of survival strategies of ANY species. Not just the host species is evolving to fight external life-forms which cause disease, also the 'diseases' are constantly changing to make their 'living'...

      There is no final state of development, no perfect organism for all times. It is a continuous flow of change and changes on a timescale way beyond our imagination and our limited timespan as humans.

      If my cat was suffering from feline leukemia, why would it be only deadly to her and not to me even if it gets into my system? I would not even notice that my immune system successfully destroyed the incoming virus, because it knows how to deal with it. So far, this virus did not cross the species barrier, yet this may change in the future, as nothing is static in life at no time!
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      Dec 18 2012: So you are suggesting if natural selection could result in eyesight, then it should have addressed diseases.

      I'm not sure why you would think that.

      Actually a few different types of eyes have evolved, vertibra share camera eye. Compound eyes and squid eyes.

      I suggest many of the comments here show a better understanding of natural selection.

      Again adaptations that promote survivability and lead to changes in gene frequency don't result in perfect beings.

      Its a bit like me suggesting if an all knowing all powerful god created the universe for human spirits, why did she do such a crappy job. 99.999999% of the universe would kill us instantly. Disease, kill or be killed nasty battle for survival.
    • Dec 18 2012: "It seems to me that the eradication of disease should be a fairly basic & straightforward result of natural selection. Defeating measles should be a walk in the park after creating a butterfly from a melted caterpillar. Maybe it's just me?"

      The measles (virus) fights back because it's also evolving, this is similar to how there are still predators and prey animals even though they've been locked in an evolutionary arms race for hundreds of millions of years.

      There are tradeoffs: some extremely primitive multicellular organisms are immune to cancer and basically immortal (they don't age) but this is because they are so primitive: for these organisms to evolve even a rudimentary nerve system they would have to give up their immunity to cancer and immortality because the cells would have to adopt far more complex mechanisms. Crocodiles are far more resistant against bacterial infections than mammals are, but since crocodiles don't mate with mammals, mammals would have to evolve a similar mechanism on their own which takes a lot of time, basically lightning would have to strike twice.
  • Dec 16 2012: Okay as others have pointed out this is also true for the diseases.