On 9/15/2011 1:24 AM, Invisible wrote:
> On 15/09/2011 03:38 AM, Patrick Elliott wrote:
>> On 9/14/2011 6:24 AM, Invisible wrote:
>>> Are fungi poisonous on purpose, or is it just a side-effect of their
>>> unusual body chemistry?
>>
>> Nothing is "poisonous on purpose", everything is a side-effect of
>> different body chemistry. It just happens that, in some cases, those
>> side effects make them a lot bloody harder for other things to eat.
>
> OK, but consider this: The venom of the Black Widow spider is "designed"
> to be lethal to insects - and indeed it is. To mammals, it's harmless.
> It has no effect on dogs, cats, mice... oh, but by freak coincidence, it
> happens to be deadly to humans. How unlikely is that?
>
> Point being, humans aren't the target. It just happens to work on them.
> Insects are the target.
>
Designed no. But if your a spider and you can't produce poison that 
effects insects, its not going to help you much. That some of them 
happen to accidentally effect other species, is not coincidence, in that 
you need the same chemical processes, on some level, in all animals. A 
poison doesn't have to do the same "identical" thing, hence the lack of 
some having an effect at all. In other cases, it may do some of same 
things, but because the poison isn't effecting the nervous system, but 
some other effect (spider venom also has necrotic effects, which kill 
tissue, regardless of *whose*, because it breaks down cells chemically, 
without needing to target specific characters "of" those).

A good example is snakes. Snakes have a very complex cocktail of organic 
chemicals. In most of them, those have been adapted to shut down pain, 
in most of the prey they go after. Since humans are not "prey", *none* 
of them should have a chemical for that. Yet, there is one in Africa, 
which does, and its not a python, or anything that might logically eat 
people. But... it might have eaten monkeys, of some sort or another, and 
a chemical that targets some nonspecific characteristics of pain 
receptors in monkeys "might" by sheer accident also effect humans, do to 
commonalities in the two nervous systems.

In any case, a "designed" venom wouldn't need 40+ different, often 
redundant, organic chemicals, instead of 3-4 very specific ones. They 
wouldn't need to contain things that have no effect on their prey, at 
all, but effect things, in some cases, that they would *never* come in 
contact with, etc. There are a lot of cases like that. Adaptations, 
which while they don't stress the animal enough to lose them, are nearly 
useless, because what they once affected is no extinct locally, and 
others where the effect of the adaptation actually is worse for other 
species, than the one it targets. Why? Because it works well enough for 
what its used for, and the coincidence that its much worse for something 
else is accident. Snakes don't "intend" to kill people, but some of them 
*will*, because we have the misfortune of happening to react **very 
badly** to their venom. It makes about as much sense to ask why this is 
the case, as though it was "designed", as to ask why some flowers 
produce pollen, which *happens* to make some percentage of people *very* 
allergic.

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