Earlier this year, there was a review of the topic in Science. It is
called "The directed mutation controversy and neo-Darwinism", by Lenski and
Miller (Science vol 259: p 188-193 (8 January 1993)).
The abstract reads, in part, "Critics contend that studies purporting to
demonstrate directed mutation lack certain controls and fail to account
adequately for population dynamics. Further experiments that address these
criticisms do not support the existence of directed mutations."
Mind you, I am not saying that I agree with the review-- I did not understand
the original papers when they came out, and I have not gotten around to
reading the review carefully yet. However, from what I do understand of
the issues, the problem ultimately is that individual mutants in bacteria
cannot be isolated, as they can in macroscopic organisms, and consequently
population dynamics must be treated very carefully in control experiments.
In several experiments redone carefully, the apparently directed mutation
goes away; however, as Lenski and Miller admit, "Of course, there are
other reports of directed mutation that have not been shown to be flawed.
But in our opinion, none of the claims for directed mutation has compellingly
excluded all of the alternative hypotheses based solely on random mutation."
the implication of the discussion is that many of the recent publications
revisit issues first asked and answered in the days of Luria, Delbruck and
I get the feeling that there may be people who perceive the experiments
reviewed in this paper as "straw men," and that the better-done experiments
were not reviewed. However, this is not a literature that I know at all,
so I can't tell if the cases discussed are a reasonable sample of the
experiments that have been done or not....
I would certainly be interested in hearing about responses to this review
article, both responses to its interpretation of the experiments it considers
and response to the research it did not cover.
bell at minerva.cis.yale.edu