The viceroy butterfly generates a toxin compound which make it distasteful to predators. Biologists agree that the viceroy must have developed this trait as a passive defence mechanism to prevent being eaten.

Let’s look at it from an information point of view.

For this to work, information about the bad taste of the viceroy must be known to the predators. This can happen by a predator eating one viceroy, discovering the bad taste, learning and never doing it again. Unfortunately, the unpalatable butterfly had to die in the process.

The second, and most important, information path is the genetic one. One way, evolution work is by the survival of the fittests. In this case the important trait of “tasting bad” dies with the butterfly and is less likely to have been transmitted to a new generation, unless (and this might be part of the answer) we consider the local population of butterfly as the evolving organism.

The question: If a successful gene is only proven successful when removed from the gene pool, how does the species evolve a trait involving this gene?

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    $\begingroup$ Possible duplicate: biology.stackexchange.com/questions/24312/… see also: biology.stackexchange.com/questions/66081/… $\endgroup$
    – Bryan Krause
    Commented Mar 20, 2019 at 20:57
  • $\begingroup$ @BryanKrause Thanks for finding the duplicate. I think your second link is probably more clear, but since that points to 24312, I used it as the dupe. $\endgroup$
    – De Novo
    Commented Mar 20, 2019 at 21:30
  • $\begingroup$ OP the reason this isn't a paradox is the title of the duplicate (natural selection occurs at a species level, not an individual level). The mechanism by which a toxin would be selected for is discussed specifically in this answer. If it helps, you should remember that natural selection acts on existing variation. So the toxin is already present in the population at some frequency. $\endgroup$
    – De Novo
    Commented Mar 20, 2019 at 21:34
  • $\begingroup$ I think the problems your two points. bring up can be summarized as evolution does not act on the level of a single organism. $\endgroup$
    – user40950
    Commented Mar 20, 2019 at 21:35
  • $\begingroup$ The post marked as duplicate talks about species/lineage selection. This is unlikely to be a good explanation for the process asked by the OP. Instead, the other post @BryanKrause suggested as duplicate (How does natural selection explain how organisms that are poisonous evolved?) is a much better duplicate IMO (and talks about kin selection among other things). $\endgroup$
    – Remi.b
    Commented Mar 21, 2019 at 1:21


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