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It is true that a lot of members of our, and most other species, suffer from cancer, but it is still not ubiquitous nor does it exist throughout the individual's life.

If a species existed, in which all, or almost all of its members suffered from the same pathology, and that pathology showed up and existed throughout the organism's life, and this pathology has always existed within the species, would that violate natural selection enough to consider the current body of theory of evolution falsified?

To be clear, it is recognized that natural selection is not the only process which occurs during evolution, but it is pretty safe to say that enough of our body of theory on evolution rests with the validity of natural selection that if natural selection were falsified, so would the body as a whole, and we would need to rework our theories.

Consider what is said in Evolutionary dynamics in structured populations.

An evolving population consists of reproducing individuals, which are information carriers. When they reproduce, they pass on information. New mutants arise if this process involves mistakes. Natural selection emerges if mutants reproduce at different rates and compete for limiting resources.

In other words, evolutionary dynamics implies natural selection. A violation of natural selection therefore would make the current theory on evolutionary dynamics less likely. Now, it could be that other processes are so powerful that they completely override natural selection, but to find a species in which natural selection has totally failed to weed out a near universal illness should present a problem for current evolutionary theory.

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closed as primarily opinion-based by kmm, David, AliceD Aug 17 '17 at 20:50

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ If the disease/illness does hinder the fitness of the species, natural selection has no pressure to stop it. $\endgroup$ – Hawkeye Aug 16 '17 at 22:13
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    $\begingroup$ Although I think @Remi.b's points about selection not being the same as evolution clearly show that this question is misguided, you could argue that aging is a ubiquitous illness that has some selection benefits. Overall, though, this question sounds like it's intended as a trap. $\endgroup$ – Bryan Krause Aug 16 '17 at 22:13
  • $\begingroup$ I am not conflating natural selection with evolution, but if natural selection is falsified, then so would evolution, at least as we view it now, which means that our entire body of theory would have to be reworked. $\endgroup$ – Daniel Goldman Aug 17 '17 at 16:36
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    $\begingroup$ @vasshu Natural selection is only one process by which evolution occurs. There is also genetic drift, gene flow, and mutation. Even if natural selection is falsified, it would not falsify evolution since there are other ways evolution occurs. $\endgroup$ – Hawkeye Aug 19 '17 at 3:28
  • $\begingroup$ True, but natural selection is a consequence of evolutionary dynamics. To see it fail to function, even in one species, would present a problem. $\endgroup$ – Daniel Goldman Aug 19 '17 at 15:19
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Very short answer

Evolution ≠ Natural Selection

Slightly longer answer

Evolution ≠ Natural Selection

You seem to equate evolution with natural selection which is the main issue. Various evolutionary processes may yield a population where all individuals suffer from a specific disease. It may not be an equilibrium state though but a state that may well last long enough to be frequently observed.

For example a bottleneck can cause a disease to reach an extremely high frequency if there was some deleterious recessive alleles in the parent population. A bottleneck is not a process that is encompass within the term Natural Selection but it is still an evolutionary process.

We actually have examples (incl. examples in humans) of populations where the prevalence of particular genetic disease is very high.

The existence of other evolutionary processes than natural selection does not violate the theory of natural selection

The existence of other evolutionary processes than natural selection does not violate natural selection theory. The theory of natural selection does not state that nothing but natural selection can affect a population's evolution.

If one were to think that the existence of genetic drift (another evolutionary process) would violate natural selection, then this person would also think that the existence of wind that would affect an apple course falling through the air would violate the theory of gravitation.

What is evolution?

Your question comes from a misrepresentation of what evolution is about. You might want to have a look at a short and intro course to evolutionary biology such as Understanding Evolution by UC Berkeley for example.

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  • $\begingroup$ I did not mean to equate the two, although our current theory of evolution is heavily dependent on natural selection. As for my understanding, I have a fair amount of bio behind me, including evolutionary biology and bio-archaeology. $\endgroup$ – Daniel Goldman Aug 16 '17 at 19:51
  • $\begingroup$ You got close with the vague reference to diseases w/ high prevalence, but this is not the same as ubiquitous existence and expressed throughout the individual's life. $\endgroup$ – Daniel Goldman Aug 16 '17 at 19:51
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    $\begingroup$ Can you please expand on diseases w/ high prevalence [..] is not the same as ubiquitous existence and expressed throughout the individual's life? I don't understand it. Do you mean high prevalence is not the same as prevalence of 1? You can have a prevalence of 1 and that would not change anything. Fixed deleterious alleles are really not uncommon. $\endgroup$ – Remi.b Aug 16 '17 at 21:11
  • $\begingroup$ Cancer, for instance, occurs in many individuals, but it is not something that almost every individual lives with for its entire life. It occurs within a fraction of the population for a fraction of the organism's life. $\endgroup$ – Daniel Goldman Aug 17 '17 at 16:38
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Evolution doesn't ensure a good quality of life, nor does it ensure a longer lifetime of a species's organism.. It only aims for the continued sustenance of the species in a changing environment.

What does being ill really mean?

  • Does it mean that the lifespan becomes smaller? No, an insect might have a smaller lifespan while being a very rapidly evolving life form.
  • Does it mean that the species would be pain-free while living? No, even humans are designed to endure chronic pain.

All the things that contribute to not being "ill", are really just things which contribute to being able to have a faster and continuous sustenance. Long life means more chances of offsprings, being pain-free gives more time and ability to mate.

Hope this answers your question! First post. This thread made me join this exchange!

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    $\begingroup$ Evolution [..] defines continuous sustenance That is a little unclear but sounds pretty wrong. Selection (and other evolutionary processes) does not necessarily minimize the probability of extinction. $\endgroup$ – Remi.b Aug 16 '17 at 20:27
  • $\begingroup$ You are right, I should change that to "Aims to" rather than "Is defined by". $\endgroup$ – BikerDude Aug 16 '17 at 21:42
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    $\begingroup$ Even "aims" would be wrong. Evolution is not conscious being attempting to do anything. You could say "tends" to avoid the agent view of evolution but even then, it would be misleading. Evolution does not necessarily tend to minimize extinction probability nor does it tend to increase individual's lifespan (whatever you mean by sustenance). A genotype decreasing the group mean absolute fitness to its own benefit will be selected for. $\endgroup$ – Remi.b Aug 16 '17 at 21:53
  • $\begingroup$ Well, I think it is agreeable that Evolution(Even though it is a phenomenon) can be attributed to doing something. For example: The Cold temperatures in the high altitudes leads to a higher chance of rain. $\endgroup$ – BikerDude Aug 16 '17 at 22:02
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    $\begingroup$ Evolution refers to the change of allele frequency (and phenotypic traits) in a population over time. It does not do anything (sorry that sounds like I'm being a pain in the neck with definitions but it may be important for our discussion). There are particular evolutionary processes that cause those changes, such as natural selection and genetic drift for example. But genetic drift and natural selection do not necessarily lead a species to increase its probability of survival (or whatever is meant by sustenance in your answer). $\endgroup$ – Remi.b Aug 16 '17 at 22:11

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