Received: by alpheratz.cpm.aca.mmu.ac.uk id IAA11508 (8.6.9/5.3[ref pg@gmsl.co.uk] for cpm.aca.mmu.ac.uk from fmb-majordomo@mmu.ac.uk); Wed, 15 Nov 2000 08:39:38 GMT Message-ID: <A4400389479FD3118C9400508B0FF2300410C8@DELTA.newhouse.akzonobel.nl> From: "Gatherer, D. (Derek)" <D.Gatherer@organon.nhe.akzonobel.nl> To: "'memetics@mmu.ac.uk'" <memetics@mmu.ac.uk> Subject: RE: Tests show a human side to chimps Date: Wed, 15 Nov 2000 09:35:04 +0100 X-Mailer: Internet Mail Service (5.5.2650.21) Content-Type: text/plain; charset="iso-8859-1" Sender: fmb-majordomo@mmu.ac.uk Precedence: bulk Reply-To: memetics@mmu.ac.uk
Vincent:
But won't the net effect of water boiling mean greater survival
rates than non-boilers, over a long enough period of time, making it in the
end a form of niche construction?
Derek:
Boiling water would certainly increase survival, especially in infants prone
to die from dehydrating enteric diseases like cholera. Rogers, if I
remember rightly, does not actually look at it from this point of view, as
he is synchronic in his analysis methods, just taking a snapshot of what
exists at a certain time and dissecting its structure (influence of
Levi-Strauss??).
Whether or not boiling changed the genetic composition of the population
would depend on the effective population size (written N subscript e in pop
gen). A small population losing _any_ members for _whatever_ reason will
experience a change in its overall gene pool composition, just by random
sampling effects, known in pop gen as 'bottlenecking' or 'founder effect'.
That's what happened to the Yuni people in California or the Pitcairn
Islanders. Even random accidents have serious evolutionary consequences.
But in a larger population it doesn't apply. If cholera kills only
non-boilers, and the population is large enough that the boiler and
non-boiler sub-groups have the same overall allele frequency, then the
partial adoption of the cultural trait will not affect the genetic
constitution of the population. In a small population, sampling variation
will mean that _any_ 2-way split of the population will produce 2 groups
with different gene frequencies - even tossing a coin. Suppose you toss a
coin and kill everybody who gets tails. In a population of 20 this will
have major consequences in terms of the genetic constitution of the
population. In a population of several million, it won't.
Likewise boiling. Suppose we just kill all non-boilers. Suppose boiling
has no inherent biological survival advantage except that we ruthless
exterminate anyone who doesn't do it. Whether or not our terrible actions
have an effect at the biological evolutionary level depends entirely on the
population size, as above. However, regardless of the genetic consequences
(or lack of them), it will have a profound cultural evolutionary effect.
Boiling will become virtually universal.
That's why genes and culture _can_ be independent replicators. Can - but
not necessarily will, of course.
Vincent:
...... that doesn't explain how water boiling reached that degree of
prevalence in the
community in the first place, or why some people took it up and not others.
Derek:
Health workers from Lima introduced it. That's how it arrived. They were
profoundly puzzled about the fact that some villagers didn't take it up and
others did. That's when Rogers (who was working for the WHO or UNESCO at
the time , I think) arrived.
Vincent:
Sounds like an interesting study. I don't suppose you have a
reference to hand do you?
Derek:
The Peruvian water boiling stuff is from the first chapter of
Rogers, E.M. and Shoemaker, F.F. (1971) Communication of Innovations. A
Cross-cultural Approach. 2nd ed. Free Press: New York.
For milk drinking, the classic memetic study is:
Aoki K (1991) Time required for gene frequency change in a deterministic
model of gene-culture coevolution, with special reference to the lactose
absorption problem.
Theor Popul Biol 1991 Dec;40(3):354-68.
Department of Anthropology, Faculty of Science, University of Tokyo, Japan.
Abstract is
"The time required for gene frequency change under natural selection in a
deterministic model of gene-culture coevolution is investigated. A discrete
generations model is formulated, and its continuous time approximation is
derived. In passing to the continuous time limit, it is assumed that the
frequency of the culturally transmitted trait does not change under oblique
(between generations) transmission. The system of ordinary differential
equations thus obtained are solved, and the dependence on the parameters of
horizontal (within generations) transmission and natural selection is
examined. The time required is found to be substantially longer when the
determination of a phenotypic difference subject to natural selection is
partly cultural rather than completely genetic. The predictions are relevant
to the possibility of the coevolution of lactose absorbers and milk drinkers
in some human populations. Alternative hypotheses are briefly discussed in
the light of the theoretical results."
and there is also quite a bit in William Durham's book, if I remember
rightly.
Durham, W.H. (1991) Coevolution: Genes, Culture and Human Diversity.
Stanford University Press: Stanford.
Durham also has an exhaustive analysis of the genetics and culture of
malaria resistance in West Africa, which goes well beyond the rather
desultory treatment that gets trotted out in most genetics textbooks. That
is really worth a read too.
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