Below I forward a copy of a post by Ian Pitchford to the listserve
"evolution" <evolution@human-nature.net>. Pritchford is at the Department
of Psychiatry
University of Sheffield, UK. His e-mail is <Ian.Pitchford@scientist.com>;
he also directs attention to the website "Darwin and Darwinism"
http://www.human-nature.com/darwin/index.html
I post it here to the CSGnet list because it seems a fair fit with the
theories I've heard expressed here that propose that evolutionary change is
in some manner dependent on control-systems. This experimental report
looks very promising for the refinement of such theory.
Tracy Harms
Bend, Oregon
···
==============================================================================
A paper of potentially major importance from today's 'Nature' Vol 396 No. 6709
Mutants in waiting
Unlike most heat-shock proteins, Hsp90 is often not required for protein
folding, but it does associate with proteins that control cell growth during
development. By surveying the properties of _Drosophila_ with impaired Hsp90
function, Rutherford and Lindquist find that almost any body structure can be
altered as a result. Under normal conditions, silent genetic variation may be
'stored up' in signalling proteins, masked by association with Hsp90. But in
times of stress, Hsp90 may be sequestered by the general abundance of unfolded
proteins, which could unmask mutant forms of key signalling components and
result in an acceleration of morphological evolutionary change, enhancing
chances of survival. In other words, prefabricated solutions to future
challenges may exist in our genes. [Article, p.336; News and Views, p.309]
_____________________
Cossins, A. (1998). Cryptic clues revealed. Nature, 396, 309-310.
SUMMARY: Darwinian evolution is often thought of as incremental and
progressive, although the fossil record indicates step-wise change in
morphological characteristics. An analysis of mutant fruit flies now provides a
mechanism for rapid morphological change, with implications for evolutionary
theory.
_____________________
Rutherford, S. L., & Lindquist, S. (1998). Hsp90 as a capacitor for
morphological evolution. Nature, 396, 336-342.
The heat-shock protein Hsp90 supports diverse but specific signal transducers
and lies at the interface of several developmental pathways. We report here
that when Drosophila Hsp90 is mutant or pharmacologically impaired, phenotypic
variation affecting nearly any adult structure is produced, with specific
variants depending on the genetic background and occurring both in laboratory
strains and in wild populations. Multiple, previously silent, genetic
determinants produced these variants and, when enriched by selection, they
rapidly became independent of the Hsp90 mutation. Therefore, widespread
variation affecting morphogenic pathways exists in nature, but is usually
silent; Hsp90 buffers this variation, allowing it to accumulate under neutral
conditions. When Hsp90 buffering is compromised, for example by temperature,
cryptic variants are expressed and selection can lead to the continued
expression of these traits, even when Hsp90 function is restored. This provides
a plausible mechanism for promoting evolutionary change in otherwise entrenched
developmental processes.