wrote in message
>
> It is well known that an organism has requirements for health.
> But my topic is: How did these requirements come to be?
>
Every organism needs a source of energy, and access to the basic
constitutents of biochemicals (carbon, oxygen, hydrogen, and then nitrogen,
phosphorous and sulphur, and then minor constituents like potassium,
calcium, zinc, and then traces of a lot more elements).

Plants are autotrophs, and pretty much synthesise everything for themselves.
The only significant thing they can't do is to fix atmospheric nitrogen -
they have to get it from the soil in the form of salts.

Animals have traded this independence by specialising on ready-made food
sources. They can't photosynthesise but they can get energy by breaking down
starches and sugars that they they obtain from eating. For each metabolite,
evolution has to answer the question "do I synthesise this or do I take it
from another organism". Most animals can synthesise vitamin C, for example,
but great apes, including humans, can't. The reason is probably because we
went through a period of a fruit diet where vitamin C was super-abundant, so
losing the pathway wasn't a disadvantage.

Now the vitamin C requirement means that we get scurvy if we try to live
entirely on preserved food.
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