Download Neutralism - Winona State University

Darwinian Selection
vs.
Neutralist Theory
I.
The neutralist ideasA. Kimura summarizes: "Most of variation is selectively neutral and hence largely
irrelevant to a population's capacity to respond to new forces of selection."
B. All the loads shouldered by genes undergoing evolution: mutational,
recombinational, balanced, genetic, etc.
C. Haldane figured out how many generations (and how much genetic death) is
necessary for one gene substitution.
D. Neutralists proposed that most amino acid changes are neutral in effect. Since
selection does not act on neutral mutations, the fixation of such alleles incurs no
genetic load and depends only on their mutation rates and on random genetic
drift.
II.
The selectionist argumentsA. Propose selection schemes that explain persistence of many polymorphisms while
only conferring a minor genetic load.
Ex. Frequency-dependant selection-incurs genetic load only when the frequency
of the relatively rare selected allele is changing but produces no genetic load
when the allele has reached equilibrium
--selection in natural populations probably lumps effects of many, individual
genotypes into large groups; fit vs. unfit. Forms a threshold.
B. Selectionists emphasize:
--Association between protein polymorphisms and ecological conditions
--Nonrandom allelic frequencies in enzyme polymorphisms
--Association between enzyme function and degree of polymorphism
--Polymorphisms for DNA coding sequences
Roots of neutral theory? Zen philosophy and Tai Chi?
Roots of selectionism? Capitalism and frontier mentality (or British equivalent)?
III.
IV.
Selected References
Kimura, M. 1983. Neutral Theory of Molecular Evolution. Cambridge University Press. NY.
Kreitman, M. and H. Akashi. 1995. Molecular evidence for natural selection. Ann. Rev. Ecol.
Syst. 26: 403-422.
Li, W-H., and D. Graur. Fundamentals of Molecular Evolution. Sinauer.
Milkman, R.(ed). 1982. Perspectives on Evolution. Sinauer.
Selander, R., A. G. Clark, and T.S. Whittam. 1991. Evolution at the Molecular Level. Sinauer.
Sober, E. 1984. The Nature of Selection: Evolutionary Theory in Philosophical Focus.
University of Chicago Press.