Re: 'evolution in action'...

On 3 Mar, 13:54, "Ron O" <rokim...@xxxxxxx> wrote:
I do not think that you have the facts straight on this issue.
Mammals only produce lactase when they are infants and being fed
mother's milk in their diet. This gene is turned off when they are
weened.

Agreed.

Apparently it saves enough energy and resources to turn the
gene off when it will not be needed to have been selected for such a
regulation.

It does if there is an energy or resources shortage, that is, a
famine. No famine, no selective pressure to repair the regulation
mechanism.

For lactose tolerance a mutation has occurred in the
regulatory region that keeps the gene turned on all the time. As long
as dairy milk is in the diet this appears to be selectively
favorable. In space with limited biospheres you aren't going to have
dairy animals except for the fabulously rich. No dairy, no reason to
keep the gene on.

No reason to shut it down, either.

The lactase enzyme is functional it is just
regulated differently.

The regulation mechanism must allow the gene to be activated during
infancy, and I think it would be unlikely for an age-dependant (or
diet-dependant) regulatory mechanism to arise without a selective
pressure. Thus it's likely that the unregulated gene will stay
unregulated, unless there is a selective pressure to repair the
regulation mechanism.

In space it would probably not be economically
worthwhile to manufacture lactose because most humans couldn't use it
anyway as adults.

It depends. But if the first colonies are made mostly of lactose-
tolerant humans, they may develop a diet which includes lactose and
then the founder effect could keep it for a long time.

It would likely be a specialty item for baby
formula.

That specialty item is made in the mammary glands of every woman. If
the space human babies still drink breast milk, they need to produce
lactase, and if the gene switch is broken, it'll stay broken unless
selective evolution repairs it.

Ron Okimoto


.

Relevant Pages

  • Research: Computing Gene Regulation
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  • Re: Article: Unravelling new complexity in the genome
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    (sci.bio.evolution)
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    (sci.med.cardiology)
  • Food, not drugs?
    ... Dietary carbohydrate modification induces alterations in gene ... carbohydrate modifications-a rye-pasta diet characterized by a low ... characterized by a high postprandial insulin response-affect gene ... We assessed the effect of carbohydrate modification on SAT ...
    (alt.support.diabetes)