> On 15/09/2011 10:32 AM, Stephen wrote:
>> On 15/09/2011 9:24 AM, Invisible wrote:
>>> I'm just wondering whether fungi deliberately manufacture substances for
>>> no other reason than to prevent them being eaten,
>>
>> Do you believe in a god?
>
> *sigh*
>
> OK, well if you want to split hairs...
>
> I'm just wondering whether the fact that many fungi are poisonous to
> large mammals is positively selected for, or a neutral trait.

In some cases, it's a survival advantage.
In other cases, it's neutral and offers no real advantage. There may 
have been a time when it WAS an advantage to protect it from some, now 
disapeared, harmfull organism.

>
> (Which is /obviously/ what I asked in the first place, to anybody who
> actually understands how evolution works.)

Yes, over very long time periods and countless individuals. Advantagous 
traits leads to higher survival rate and more offsprings. Disadvantagous 
traits leads to earlier death and less offsprings.

>
> The tea tree manufactures caffeine for no reason other than to control
> pests. It is of no "use" to the plant itself, it's just poisonous to
> certain insects that try to eat the plant. If there were no insects, the
> tree wouldn't need to make caffeine at all. This is "deliberate toxicity".

Nothing deliberate here.
A pland had a slight random mutation and started making caffeine. By 
chance, it killed some insects that where eating the plant, and some 
times killed it. Maybe those insects also eated the seeds of flowers, 
reducing the number of offsprings.
That plant chances of survival thus increased, leading it to have more 
decendents.

Similar to the production of vitamin C by plants. It protect them from 
some infections. It's actualy toxic to some fungi and bacterias.

>
> Other substances, however, are manufactured as part of an organism's
> internal metabolic processes. As hormones, as intermediate compounds, as
> storage, whatever. A few of these just happen to be toxic to other
> species. This is "accidental toxicity".
>
> None of this is intended to imply /actual concious intent/. It's just a
> figure of speech. Sheesh...

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