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theropod manus digits & shifting balance theory



Mentioned here re: theropod hands (?II-IV or ?I-III),
Sewall Wright's shifting balance theory (like
bifurcation/game theory/fast-slow dynamical systems)
is of profound importance to understanding ongoing
processes in dinosaur evolution (and extinctions) as
well as pre-K/T inferences.
The concept was prematurely rejected by Jerry Coyne et
al. in 1997 in favour of Fisher's concepts of "mass"
selection, as iterated by Endler in 1986. Sewall
Wright's concepts, to use an example:
traits in an allosaur are in an "adaptive valley",
and, in various populations, may in fact be rather
strong, so that in time these apomorphies enter larger
populations. Adaptations of the allosaur populations
are enhanced: genetic drift/migration/selection reach,
as it were, an equilibrium. The adaptation, e.g., of
an allosaur in an arid environment vs. humid forests
is more than living with less H2O; rather, the
embryological and morphogenetic changes in a breeding
population of allosaurs > speciation. In fact, as
Dieckmann/Doebeli have proposed, the time frames for
sympatric speciations may be shorter than some have
presumed. On a genetic level, the assortative matings
in the genome for an allosaur trait would be
determined by how many loci are creating the trait
itself.
See further:
N.H. Barton & S. Rouhani, 1991. The probability of
fixation of a new karyotype in a continuous
population. Evolution 45:499-517
N.H. Barton & S. Rouhani, 1993. Adaptation and the
"shifting balance". Genetics Research 61:57-74
J.A. Coyne, N.H. Barton, Michael Turelli,1997.
Critique of Sewall Wright's shifting balance theory of
evolution. Evolution 51(3):643-671
J.A. Coyne, N.H. Barton, Michael Turelli, 2000. Is
Wright's shifting balance process important in
evolution? Evolution 54(1):306-316
J.A. Coyne, Brian Charlesworth, S.F. Elena, V.S.
Cooper, R.E. Lenski, 1996. Mechanisms of punctuated
evolution. Science 274:1748-1750
Ulf Dieckmann & Michael Doebeli, 1999. On the origin
of species by sympatric speciation. Nature 400:354-357
S.L. Peck, S.P. Ellner, Fred Gould, 1998. A spatially
explicit stochastic model demonstrates the feasibility
of Phase III of Wright's shifting balance. Evolution
52(6):1834-1839
S.L. Peck, S.P. Ellner, Fred Gould, 2000. Varying
migration and deme size and the feasibility of the
shifting balance. Evolution 54(1):324-327
S. Rouhani & N.H. Barton, 1987. Speciation and the
"shifting balance" in a continuous population.
Theoretical Population Biology 31:465-492
S. Rouhani & N.H. Barton, 1993. Group selection and
the "shifting balance". Genetics Research 61:127-136

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