Re: Fishy question

In article <1ief6jj.1g93xoq5avlogN%spam@xxxxxxxxxxxxxxxxxxxx>,
spam@xxxxxxxxxxxxxxxxxxxx says...
Gerry Quinn <gerryq@xxxxxxxxx> wrote:

In article <1iedaer.1hynaww1o8f7ciN%spam@xxxxxxxxxxxxxxxxxxxx>,
spam@xxxxxxxxxxxxxxxxxxxx says...

My argument is based on three parts:
(1) many chemicals are toxic
(2) we are immune to chemicals we are most commonly exposed to
(3) we are not commonly exposed to all the chemicals in an alien
biosphere

IOW, (2) says our own biochemistry has evolved so that the majority of
chemicals in our own biosphere (i.e. those whose primary function is not
defense or attack) are not harmful.

What about chemicals in the environment we are not normally exposed to?

Chances are it's related to other plants. ObSF: _Little Shop of Horrors_
(and a few serious horror movies, _not_ including _The Day of the
Triffids_. As I recall it, triffids were probably a bio-weapon.)

For example, the interior juices of a random plant we don't use for
anything.

These are unlikely to be deadly to the touch.

If it evolved in isolation from any of our ancestors for, say, a hundred
million years, it might be a bit strange. Is that long enough? Even if
it evolved from a completely different life-creation event (there was an
article about the possibility[*] in New Scientist recently), if it
co-evolved with normal earth life for, say, a billion years but has been
separate for another three billion, that would still be a quarter of
evolutionary history where both types of life would evolve mechanisms to
cope with the other.

Most metabolically active compounds in the juice will not be highly
chemically active (very acidic etc.). They will be designed to interact
with other compounds in the plant. Not with us. So I'm guessing pretty
inert, on the whole. There will be enzymes that have no effect on us,
sugar and proteins (or analogues) that are indigestible or moderately
toxic, fats that might very well be identical (not too many options for
fat). I'm assuming a water-carbon-oxygen planet in which there's not
something obvious amiss, like a smell of cyanide pervading the air. (Of
course we can often smell H2S on Earth - it might be that the planet has
a lot more of this or something similar, and in my view that would
probably indicate the main chemical threat to human life on such a
planet.)

Whereas truly *alien* life would be something we had previously never
come into contact with.

It occurs to me that a lot depends on how determined our own
biochemistry is. We don't even know whether our genetic code is
"optimal" in some way, or whether the 3-base pair coding for an amino
acid is arbitrary.

I've an idea it has been demonstrated that the code can be changed
without obvious ill effects. Of course it is probably not entirely
arbitrary in the sense that it is affected by its evolutionary history.

If alien biospheres evolve to basically the same biochemistry, then that
would be a strong counter-argument. I think my (speculative) argument
depends on the possibility of exotic life.

Still carbon-based etc. - I'm not talking about silicon life, or liguid
ammonia life. I think you both would agree with we would not enjoy
swimming in lakes of liquid ammonia, or molten brimstone! :-) Or would
you? There's no *obvious* reason why plants based on a chemistry that
operated at over the boiling point of water should be harmful to us:
there are no selection pressures driving them that way! :-)

Either way, the risk of accidental poisoning on such a planet, even if
you are right, would be one of the lesser risks. I do think there might
be an issue with lesser differences, as I said above - for example if
everything on the planet uses HCN, or CO, or H2S etc., much more than on
Earth.

Jonathan
[*] I use "possibility" loosely. :-) I don't believe it for a moment.
The idea that there could be bacteria with different biochemistry and no
common ancestor to the usual kinds *on earth* seems completely
implausible to me. But there's no harm in looking for it.

If bacteria evolve from seeds drifing from space, it could then happen
in 'snowball earth' type scenarios, if the first Earth organisms were
heavily suppressed for a time, allowing the new types to establish a
foothold. Two unlikely steps required, though.

- Gerry Quinn




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