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Population Genetics
Robert Snower (rs222@WORLDNET.ATT.NET)
Fri, 2 Aug 1996 21:23:48 +0000
Thanks for the assistance on population genetics to
"John H. Relethford" <relethjh@oneonta.edu>
Ralph L Holloway <rlh2@columbia.edu>
"Dwight W. Read" <dread@ANTHRO.UCLA.EDU>
Ronald Kephart <rkephart@osprey.unf.edu>
I really should read up on the subject, but how about this?
Problem: to define selection at the group level vs. selection at the
individual level vs. selection at the gene level.
Solution:
1. Selection at the group level.
Example: a population of three different armies, A, B, and C. A and B
are fighting each other. A loses, and becomes extinct. B and C survive.
Group selection involves a change in the frequency of each kind of group
(A,B or C) in the total population of groups. Before the war the freq. of
each group equals one-third. After the war, the freq. of B equals one-half,
and the freq. of C also equals one-half. So there has been a change of
group frequency from one-third to one-half for the surviving population of
groups.
Now I am going to call it 100 percent group selection if there is zero
change in the genetic constitution of the individual soldiers within these
surviving groups. But if, accompanying the group frequency change, there
was some change in the average RELATIVE (differential) genetic constitutions
of the individual soldiers, then it is not total group selection, but
partial; e.g, if the group change of one-third to one-half is 9 times
greater than the amount of change in the individual soldiers, it is a 90%
group selection, and a 10 percent selection at the individual or gene level.
2. Selection at the individual level.
It is 100 percent selection at the individual level and zero percent
selection at the gene level if the genetic constitution within each
individual remains absolutely unchanged, while the proportions of each kind
of individual changes, e.g., the proportion of people over 6 feet tall. Of
course, the gene frequencies in the entire population change, as it evolves
purely at the individual level: the kinds of people do not change, but the
proportion of each kind in the total population changes. (An unlikely
prospect.) If the change in the proportions of these kinds of individuals
is, on average, only one-fouth as great as the average gene frequency change
in the individuals, then it is a 75 percent selection at the gene level, and
a 25 percent selection at the individual level.
3. Selection at the gene level.
If the amount of change in the gene frequency of the entire population is
the same as the amount of change in the frequency of each kind of
individual, then the selection is entirely at the level of the gene, and not
at all at the level of the individual. Or at the level of the group.
It seems the first and second paragraphs (group selection) should be
amended, to a zero change in the proportions of each kind of genetic
constitution (kind of individual), not zero change in the proportion of each
genetic constitution. But the latter implies the former.
Best wishes. R. Snower rs222@worldnet.att.net
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