Re: Haldane's Dilemma and quantitative genetics

Joe writes
:
In article <e7h3ki$17cl$1@xxxxxxxxxxxxxxxxxxx>,
Perplexed in Peoria <jimmenegay@xxxxxxxxxxxxx> wrote:
But recently, I was struck by the
idea of treating the count of advantageous alleles in an individual
as a quantitative trait, and looking at the rate of change in this
trait using Price's equation and/or the 'Breeder's Equation'.
....
Question for ReMine, Felsenstein, or anyone else familiar with what
ReMine calls "the cost literature": Has anyone published anything
along these lines?

Essentially, no. Though there was, in the late 1960s, some concern with
whether truncation selection that tossed out the individuals that had the
most unfavorable alleles would reduce the cost. Also I notice that
Peter O'Donald had a relevant paper. These citations are from my 1971
paper:

Maynard Smith, J. 1968. "Haldane's Dilemma" and the rate of evolution.
Nature 219: 1114-1116.
Sved, J. A. 1968. Possible rates of gene substitution in evolution.
American Naturalist 102: 283-293.
O'Donald, P. 1968. "Haldane's Dilemma" and the rate of natural selection.
Nature 221: 815-816.

Looking for citations to O'Donald's paper I also find two I have not read:

Phelps, F. M. 1991. A unifying model for the substitutional genetic load
IMA Journal of Mathematics Applied in Medicine and Biology 8 (1): 31-56.
Charlesworth, B. 1984. The cost of phenotypic evolution.
Paleobiology 10 (3): 319-327.

Perhaps those will be relevant too.

This is my opportunity to be the group's curmudgeon for the fortieth
time, but these models are not at all representative of how evolution
works and have almost no value in advancing any physical understanding
of the evolutionary process. If I can't be any more blunt and offensive
than that, I don't know how.

The evolutionary clock does not run at any where near a constant speed.
Filled ecological niches occupied by highly coevolved communities are
very difficult to invade, and thus evolution tends to come to almost a
dead stop in such situations. Intense competitive interaction doesn't
allow much change.

Moreover, the presence of a biogeographic map, which is ignored in
standard mathematical genetics, renders the substitution of neutral
changes almost impossible. A novel neutral mutation in an individual
must compete with its sibling competitors coming from all directions,
and because the change is neutral, it has no selective advantage for or
against it by definition, thus if it is to survive, it must climb
against the Gambler's Ruin tide, a Markovian process that virtually
guarantees not only the new mutation's relatively immediate elimination
but also a very short time on the biogeographic map.

Evolution does not occur in a constant-selection panmictic pool. Rather
it occurs in bursts, appearing almost as explosions, either following
episodic catastrophes or invasions into novel adaptive zones. These are
the times when competitive pressures are released.

We now have a mountain of evidence that evolution operates in this way.
Small disruptions tend to act as "diversity pumps," while large
catastrophes vacate sufficient ecological space so as to act as
"complexity pumps." Two truly excellent recent papers that quite
clearly demonstrate this phenomenon are those by Johnson et al. (2006)
and Bambach et al. (2002).

The first paper outlines the recent evolution of the cats as being
governed by the rise and fall of global sea levels. I consider the
paper important enough to have put up a copy on one of our auxiliary
servers:

http://67.41.4.238/cats.pdf

Falling global sea levels during the Late Miocene and Late
Pliocene/Pleistocene appears to have introduced bursts of evolutionary
invention into the Felidae. It's during these epochs that previously
isolated populations were free to migrate into new environments,
resulting in new adaptive radiations. Pay special attention to their
Fig. 1, which is best viewed when rotated 90º leftward, so that the
sea level chart is horizontal. In this orientation, the correlation
between lowered mean sea level and the bursts of evolutionary novelty
within the diversification of the cats is made most clear.

But even more striking than that are the global catastrophes of the
Permo-Triassic and Cretaceous-Tertiary, events which vacated most of
ecological space, and thus removed all "costs" associated with allelic
variations for a bit of time. The evidence accumulated by Bambach et
al. (2002) strongly suggests that such global catastrophes were
essential in creating even more profound complexity pumps. Their paper
is available on-line at:

http://www.pnas.org/cgi/reprint/99/10/6854.pdf

and is explained in some detail in the first several slides of Andy
Knoll's talk at:

http://aics-research.com/lotw/lotw20060515.html

Evolution proceeds when the costs of substitution disappear, but those
costs are never governed by some internal mechanism, but only by each
phyletic lineage's external competitive milleu.

Wirt Atmar



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Relevant Pages

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