Re: Picts (the painted ones)


<mack54@xxxxxxxxxx> schreef in bericht
news:1157702396.860283.17800@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Thanks for that Lesley, but does this not prove that there is a genetic
difference? I mean, a lot of black people in the US, for example, carry
the gene, so I would presume it was not purely environmental. Correct
me if I'm wrong on this because my knowedge of genetics is down to
reading all Richard Dawkins' books. Having said that, would there be a
mutated gene (a 'Selfish' gene) in some 'races' and not others, that
allow members of that 'race' to acquire certain diseases? If this is
so, would it not be the fact that some 'races' were genetically
different to others?

Of course there's some genetic variation in humankind. You just have to look
around a room to see it, and it's healthy because a community with broad
genetic variation has more flexibility to deal with new pressures. The
variation comes within the fine tuning. That's why, if 2 blue-eyed people
have a child with brown eyes, people will take a good look at the
milkman....
The occurrence of a gene in an individual is not due to its environment
(that's the old Lamarckian idea that if giraffes stretch their necks to
reach higher food, their children will have longer necks), but the relative
numbers of people in any community carrying a given gene can be at least
partially linked to the environment if possession of that gene increased (or
decreased) the chances of that person living long enough to have children,
and raise those children to breeding age. Thus a giraffe that was born with
a longer neck, in times of food shortage, might be a more successful parent
than one with a shorter neck because it could reach more of the limited
supply of food. Had sleeping sickness been a disease of cooler climes, there
would have been a larger proportion of people with sickle cell within a
white community.
Of course this is a simplified case - other factors are always involved.
Antibiotic resistance in bacteria is simpler and based on the same
principle. As with humans, a culture of bacteria is a mixture of slightly
different individuals - every time they divide, there's a chance of a
copying error or a mutation. In good times, with plentiful nutrients, they
all do well. If times get hard - for example because food gets short, any
bacterium that can reduce its lifestyle requirements of a minimum will have
an edge. Making and carrying around an enzyme such as penicillinase under
normal conditions will either have no effect (good times) or be a
disadvantage (bad times) because the bug is wasting energy making it. If
someone then makes an environmental change by adding penicillin, having the
enzyme suddenly becomes an advantage and the proportion of
penicillinase-carrying bugs in the community will increase. Even then, it's
not a black/white situation - some bugs will have just a bit of resistance,
a few (because they're normally carrying too much baggage so the others can
out-compete them for other nutrients) will have a lot of resistance. If the
environmental pressure is kept up, the sensitives will die out and there
will be more nutrients for the others. Numbers of the very resistant ones
will gradually build up (it takes time to go from 0.5% of the community to a
significant number) and as the penicillin concentration rises, they'll
become dominant (which is why it's important to finish a course of
antibiotics even if one feels better - you have to hit the resistant bugs on
the head as well.

The gene has to be there, and the environmental pressure has to favour it
over those without the gene, or with a different version of it, for it to
build up within a community. Another example - all those dreadfully in-bred
dogs that get paraded as "best of breed" at Crufts every year. The genes
producing an extremely long back (or an extremely flat face, or ears that
brush the ground) could be said to be favourable in an environment where the
providers of food favour those attributes, and the dog with the extreme
version will have a higher breeding success than dogs with lesser versions
of these attributes. If something happened, and dogs had to fend for
themselves, all of these attributes would become disadantages (if you can't
breath well, you can't run fast enough to catch your own prey and keep it
from others) and they'd gradually disappear.

End of lecture.
Lesley Robertson


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