Directed or Adaptive Mutation?
Alan McCarrick,
The Christian
Academy, Media, PA
From: PSCF 50 (March 1948): 4.
A confusing group of terms (directed, adaptive, selection-induced, Cairnsian) describing mutations has spread in the scientific literature. As I see it, two basic areas can be distinguished: (1) an increase in the beneficial mutation occurring in stressed organisms;1 and (2) the imposition of a specific selection on large numbers of organisms in order to find and amplify certain novel mutations.2 The first aspect is most important to the evolution/creation discussion, the second to the pharmaceutical industry.
In the September 1997 issue of Scientific American, Tim Beardsley reviewed the current Adaptive Mutation situation.3 The possibility that living organisms possess the ability to select for beneficial mutations when stressed has challenged the conventional notion that mutations are purely random events and overwhelmingly harmful. The starting point was a 1988 article by Cairns et al.4 In those experiments, bacteria deprived of the ability to utilize lactose were plated onto media with only that food source available. Cairns reported a significant increase in the occurrence of mutations that restored the lactose utilization ability compared with the same bacteria living with other sugars available.
The most conservative explanation is that cells may simply sustain higher rates of random mutations (hypermutation) under stress. This may be for no other reason than that the resting bacteria experience a breakdown of their normal biochemical processes. Therefore, rare beneficial mutations will numerically occur more often. A more radical explanation is that the genetic tool box of cells selectively mutates portions of its DNA with a much higher likelihood of achieving beneficial results. A debate of these issues can be found in Science.5 In my opinion, the weight of evidence seems to be on the side of non-random mutation (shades of Lamark!). God seems to have incorporated into life the ability to "find a way."
©1998
Notes
1J. Cairns, J. Overbaugh, and S. Miller, "The Origin of Mutants," Nature 335 (1988): 142ñ5 and A. Gillis, "Can Organisms Direct Their Own Evolution?" Bioscience 41 (1991): 202ñ4.
2M. Wright and G. Joyce, "Continuous in Vitro Evolution of Catalytic Function," Science 276 (25 April 1997): 614ñ7 and G. Joyce, "Directed Mutation," Scientific American (December 1992): 90ñ7.
3T. Beardsley, "Evolution Evolving," Scientific American (September 1997): 15ñ8.
4J. Cairns, J. Overbaugh, and S. Miller, "The Origin of Mutants," Nature 335 (1988): 142.
5A series of letters with references in Science 269 no. 21 (July 1995): 285ñ9.