Ontogeny & Phylogeny: IV. Phage lambda again.

Mike Zwick mezwick at ucdavis.edu
Thu Apr 28 09:12:41 EST 1994


In article <2pnbdl$omt at canopus.cc.umanitoba.ca>, xia at cc.umanitoba.ca (Xuhua
Xia) wrote:

> Such a guess may be thought to be trivial, but it is not. There are
> 50 or so genes in the phage DNA, including a number of genes that
> make the head proteins and a number of genes that make the tail
> proteins. Why should not the genes for the head and tail proteins
> be expressed first? It is optimality models that allow us to
> predict, a priori, that head and tail proteins should not be made
> before DNA replication because otherwise it would be like buying
> many gift wrappers without buying any gift.

This simply doesn't logically follow - one can easily imagine a scenaro
where the head and tail proteins get translated first in order to provide
the proper context for DNA replication.  It is not optimality models which
drive the predictions, rather someone just did the experiments and
determined the answer and made the optimality model explanation afterwards.
 There are many examples of molecular processes in evolution that do not
appear to be optimally designed (i.e. as a human engineer might design a
system).

> (I should memtion that Darwinian theory of evolution, with its
> conclusion that all organisms in nature should evolve towards
> maximizing fitness under natural selection, is essentially a
> justification for the use of optimality models in biology. 

This is absolutely not correct.  While natural selection may cause
populations to evolve towards some optimum peak on the fitness surface, it
is not clear that they will ever reach that peak (and thus fulfill the
prediction of the optimality model).  Thus natural selection is not a
"justification" for use of optimally models - indeed one can easily imagine
temporally or spatially varying selection models that never reach the
optimum phenotype.


-- 
mike zwick
mezwick at ucdavis.edu
Department of Ecology and Evolution
Center for Population Biology



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