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Science Frontiers ONLINE No. 64: Jul-Aug 1989 |
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Directed Mutation
Dear reader, things have a way of working out serially. For several months, we have had in our possession a paper from Nature, by J. Cairns, of Harvard, plus some passionate correspondence stimulated by the paper. Now that the circle-forming sheep have provided a good introduction, we will jump into the fray, too.
Basically Cairns (in Nature) and B. H. Hall (in Genetics) say that organisms can respond to environmental stresses by reorganizing their genes in a purposeful way. Such "directed mutation" shifts the course of evolution in a nonrandom way.
Such a conclusion was like waving a red flag in front of the evolutionists. R. May, at the University of Oxford, complained, "The work is so flawed, I am reluctant to comment." On the other side, a University of Maryland geneticust, S. Benson, comments, "Many people have had such observations, but they have problems getting them published."
Our template in this discussion is an article by A.S. Moffat in American Scientist. She says, "The stakes in this dispute are high, indeed. If directed mutations are real, the explanations of evolutionary biology that depend on random events must be thrown out. This would have broad implications. For example, directed mutation would shatter the belief that organisms are related to some ancestor if they share traits. Instead, they may simply share exposure to the same environmental cues. Also, different organisms may have different mutation rates based on their ability to respond to the environment. And the discipline of molecular taxonomy, where an organism's position on the evolutionary tree is fixed by comparing its genome to those of others, would need extreme revision."
What sort of experiment did Cairns do to cause such a ruckus? In particular, he studied E. Coli bacteria. Normally, these bacteria cannot metabolize the sugar lactose. Cairns exposed the E. Coli to a sudden dose of lactose, demonstrating that if the bacteria must have lactose to survive, they quickly cast off the two genes that inhibit their metabolizing of lactose. Of course, the experiments were more complicated than this, but the fundamental finding was that the bacteria mutated so that they could use lactose much, much faster than chance mutation would permit, stastically speaking.
The battle lines are forming. A sup-porter of directed mutation, J. Shapiro, of the University of Chicago, is quoted as follows in Moffat's article:
"The genome is smart. It can respond to selective conditions. The signifi cance of the Cairns paper is not in the presentation of new data but in the framing of the questions and in changing the psychology of the situation. He has taken the question 'Are mutations directed?' which was taboo, and made it an issue that people will now do experiments on."
(Moffat, Anne Simon; "A Challenge to Evolutionary Biology," American Scientist, 77:224, 1989.)