Date: Mon, 26 Apr 1999 09:05:25 +0200
From: "Gatherer, D. (Derek)" <D.Gatherer@organon.nhe.akzonobel.nl>
Subject: RE: Darwin and Lamarck
To: "'memetics@mmu.ac.uk'" <memetics@mmu.ac.uk>
Chris:
'.......then I saw
some research on fruit flies which Lynn Margolis had ( don't know who did
it) which
showed very clearly that changes to an adult fly caused by environmental
factors
where then somehow transmitted through subsequent generations, and not via
the conventional DNA etc.I don't recall much of the detail.'
I think this must be Margolis referring to the experiments Waddington did
back in the mid-1950s. Fruit fly eggs were treated with ether and it was
found that the flies that were born from these eggs had cross-veins in
unusual places on their wings. Waddington found that there was a dose
response curve: more ether, more cross-veins. This is a teratological
effect, rather like administering thalidomide to human mothers causes birth
defects etc.
But then Waddington lowered the dose to a level where very few flies
developed cross-veins. These were deemed to be ether-sensitive flies.
Breeding them together for several generations, and maintaining the
selection pressure, it was possible to get ether-super-sensitive flies.
Eventually Waddington obtained flies that were born cross-veined without
exposure to ether.
This is genetic assimilation. The initial cross-veined phenotype was a
cellular response to an environmental toxin. But within the fly population
there is genetic variation which can contribute to a a greater tendency to
display that cellular response. Continued selection for the 'learned'
response, increases the frequencies of the appropriate alleles, so that the
degree of environmental insult required to produce the response becomes less
and less as the generations pass. Eventually the response is constitutitve.
As far as I'm aware there aren't too many other examples of genetic
assimilation that are as well studied as this. The relevance of the idea to
memetics is that in situations where learned behaviours are very necessesary
to survival, there will be selection for any genetic variation which either
a) makes production of the learned behaviour easier
b) can make production of the learned behaviour instinctive, thus avoiding
the need for learning at all.
So what begins as memetic ends up as genetic (but only if the selection
pressure is sustained for long enough, and only if there is the required
genetic variation in the population)
The question is: has this really happened in human evolution??? I struggle
to think of an original example. Dennett has some in Consciousness
Explained.
Derek
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