I wonder whether developing deadly toxins in the organism's body is always or usually a defensive strategy rather than a by-product.

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    $\begingroup$ I don't understand the question, spiders, snakes, etc... use it for external digestion of their prey. $\endgroup$
    – inf3rno
    Oct 28, 2014 at 22:10
  • $\begingroup$ @inf3rno I wouldn't say it that generally. Animal venoms tend to be a complex mixture of ingredients, with some components that paralyze a victim, while other components may cause death or digest tissues. Snakes don't use external digestion, they swallow the prey whole. $\endgroup$
    – user137
    Oct 28, 2014 at 22:51
  • $\begingroup$ @inf3rno I do not refer to venom used as a weapon. I mean toxins in somatic tissues. $\endgroup$
    – Anixx
    Oct 28, 2014 at 23:15
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    $\begingroup$ There's certainly a spectrum here, from the monarch butterfly(and others) who find their poisons in the environment and store them in their tissues, to some kinds of shark that have high urea contents as a result of their metabolism. The sharks probably retain some of the urea they would otherwise excrete for defense, but I'm not actually certain. If I understand the question correctly it's asking about poisonous organisms, not venomous ones. The difference is crucial to addressing this question. $\endgroup$
    – Resonating
    Oct 29, 2014 at 4:40
  • $\begingroup$ @JeremyKemball +1 venom and poison are different terms, I forgot that too... $\endgroup$
    – inf3rno
    Oct 29, 2014 at 7:35

1 Answer 1


Developing anything by the body takes energy so generally only useful products are conserved. If some sort of mutation caused an organism to produce some sort of by-product that also happened to be toxic to its predators, then that organism is more favored to survive. No species ever starts producing something with the intention of toxicity in a predator/consumer of said species.

These xenobiotics that the plant/animal produces then can either be selected for because they're useful in whatever pathway they are a by-product of. Or they can be conserved because then this by-product has a defense use, regardless of whether the pathway its part of is necessary. Or both could happen, it could be doubly selected for.

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    $\begingroup$ needs references.. $\endgroup$ Oct 30, 2014 at 6:50

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