Reflectorites
On Mon, 16 Oct 2000 20:29:34 -0500, Susan Brassfield Cogan wrote:
[...]
>>SB>Wesley was talking about isolating natural selection from drift and my
>>>understanding was that he was talking about populations over a large amount
>>>of time.
>SJ>>Why does Susan think that Wesley *needs* to see "natural selection" in
>>"populations over a large amount of time"?
SB>I'm sorry, since you (mis)quoted Wesley originally, I thought you had been
>following his conversation.
If Susan claims I "(mis)quoted Wesley originally", she should state: 1) what
was the original context; and 2) why she thinks my quote was not in that
original context..
>>SB>You see natural selection every time you spray for roaches or
>>>don't take all your antibiotics.
>SJ>I would have no problem with this if it *was* natural `selection', i.e.
>>differential survival and reproduction.
>>
>>But as a matter of interest how does Susan *see* "natural selection
>>*every* time you": 1. "spray for roaches" or 2. "don't take all your
>>antibiotics"?
SB>You should get your doctor to explain the antibiotics to you. I'm surprised
>he/she hasn't already. The doctor will warn you to take *all* the
>antibiotics, in order to raise the chance that you will kill all of them
>(cause a little extinction, if you will). If you only take some of them,
>you kill off all the weak ones leaving only the strong ones. Then after a
>while you have only the strong ones in your body and the antibiotics don't
>have any effect on them. Perhaps you should read some the WHO stuff that's
>been coming out lately on this subject.
I am a former Hospital Administrator so I am well aware that bacteria
become resistent to antibiotics. And I said "I would have no problem with
this if it *was* natural `selection'"
But that wasn't my question. Susan said she could "see natural selection
every time you ... don't take all your antibiotics" and I asked "how does
Susan *see* "natural selection *every* time you" .... "don't take all your
antibiotics"?
>SJ>In the case of 1. if a "roach" survives after Susan sprayed it with
>>insecticide, how does Susan "see" that it did not survive because she
>>did not spray it properly? Also how does Susan "see" that the "roach"
>>does not die later without offspring?
>>
>>As for 2. how does Susan "see" bacteria, let alone that they have been
>>naturally `selected' against the effects of the "antibiotics"?
SB>I'm not sure what you are asking here. I don't need to "see" them to know
>that the Suprax which worked on my infection last time isn't working now.
How does Susan know it was "natural selection" that is the reason her
antibiotic "which worked on" her "infection last time isn't working now"?
How does she know it wasn't: 1) A different strain of bacteria; 2) random
genetic drift; 3) lateral gene transfer; 4) or a bad batch of antibiotics? There
is even some evidence that bacteria can 5) evoke a Lamarckian inheritance
of aquired characteristic directly.
SB>The people who developed Suprax in the first place "saw" the bacteria being
>selected by it. That's why it's on the market now.
I am not questioning that a drug company might be able to see natural
`selection' working in a carefully controlled laboratory experiment.
What I am questioning is how *Susan* sees it.
>SJ>Finally, if Susan did manage to "see" the above, how does she know
>>that what she sees is not natural `selection' but instead genetic "drift"?
SB>Drift? drift is slow. Natural selection is fast.
It more like the other way around. As I posted before, in one of my
Biology labs last semester we simulated drift and natural selection, and it
was *amazing* and completely counter-intuitive to all of us how fast and
dominant over natural selection drift is in a small, isolated population,
SB>It's my understanding
>(someone more knowledgeable should jump in here) that drift only pertains
>to genes that don't have immediate survival value--like red hair or the
>ability to curl your tongue from side to side.
No. They (or at least the tongue curl example) are caused by recessive
alleles.
Drift has nothing especially to do with those. Drift is just random stochastic
(i.e. statistical) changes that happen in small populations. Like tossing two
coins a small number of times. If H(eads) = a favourable allele and T(ails) =
an unfavourable allele, there is a small but real chance that only the
unfavourable T alleles will reproduce/survive and the H alleles would be
eliminated from the population. For example in a small population on an
island the animal with the selectively advantageous H allele gets killed by
lightning.. In a large number of flips (= in a large population) this is very
unlikely to happen
Steve
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"Biology is the study of complicated things that give the appearance of
having been designed for a purpose." (Dawkins R., "The Blind
Watchmaker," [1986], Penguin: London, 1991, reprint, p.1)
Stephen E. Jones | Ph. +61 8 9448 7439 | http://www.iinet.net.au/~sejones
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