Surprise results with mutant bacteria
Everyone knows that mutations in living organisms occur in a random way - but is it really true? Random mutations are a key ingredient in the neoDarwinian model of evolutionary change. They guarantee, at least in the minds of those who believe it to be true, a source of novel variability on which natural selection forces can work to drive the process of evolutionary change.
Many of us have been unimpressed by the combined power of mutations and natural selection to achieve the diversity of body plans and complex organs found in the living world. We discover in organisms the kind of complexity which forces the conclusion that they have been designed and created by God. We do not expect animals, nor even a single cell, to be products of natural processes. To our minds, this is far less likely than finding a watch, or a factory, that had not been designed by man and constructed by human skill.
Take any of the senses, for example, and think of the underlying mechanisms. Whether we consider sight, or hearing, or taste, or smell, or touch: we soon find ourselves out of our depth in understanding the complexities involved. The human hand is a marvel of bioengineering and, despite the investment of millions of pounds in research and development, the artificial hands fitted to the most expensive of robots are far from achieving a performance comparable to the real thing. It is paradoxical to see scientists and engineers emphasising complexity and the need for intelligent design, and at the same time hear theoretical biologists insisting that a combination of random mutations and natural selection is sufficient to explain the origin of mindblowing living systems.
Despite severe criticisms of the inadequacies of neoDarwinism to explain any changes of importance, these theoretical ideas are still dominant in academic circles. 1991 saw the publication of research results which tested a prediction of the theory and showed it to be inadequate. Professor Barry Hall of Rochester University, New York, is responsible for the revolutionary findings which appeared in the July 1991 issue of the Proceedings of the National Academy ofSciences, USA.
Hall worked with the bacterium Escherichia coli, which is one of the popular subjects selected for genetic research. He took a mutant strain of a bacterium which was unable to manufacture a specific kind of food from its environment. By supplying this food to the colony, Hall could keep the mutants actively reproducing. If, however, the nutrient was not supplied, the population would become inactive, and would cease growing. Previous work by Hall, and others, had been concerned with the few individuals which had experienced the single gene mutation necessary to make the nutrient themselves. The cultures in which this mutation occurred were soon found to be thick with reproducing bacteria. Hall went on to develop experiments so that two independent mutations were necessary for survival. He was able to predict the rate at which these double mutations would occur, and also determine the rate experimentally. The result was startling: `Double mutations thus occurred more than eight orders of magnitude more frequently than would be expected if the two mutations were independent events.'His conclusion was that these mutations are not occurring randomly, and that the bacterium possesses a mechanism for increasing the rate of advantageous multiple mutations. Although the supporters of `orthodoxy' fought back, as indicated in New Scientist (21 September 1991, 30-34), Hall stood his ground. He argued that the mutations appear to occur simultaneously rather than randomly, and that no evidence for other changes in the DNA sequences have been found.
To the layman, the relevance of all this might seem obscure. What has this to do with evolutionary theory? Why should I be interested in experiments on a mutant bacterium? The best way of thinking about this research is that it appears to have falsified a prediction of neoDarwinism - and this is what makes it revolutionary! Hall was reported in the Daily Telegraphas saying:
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`The old paradigm that says that mutations are absolutely random with respect
to their usefulness is dead - and that's going to be hard for a lot of biologists
to swallow.'
The most important next step for this research is to investigate the mechanisms involved: how does the cell know that it must fix a certain mutation? Is this what is really happening? There must be a genetic or biochemical explanation for the observations. Until we have a greater knowledge of the situation, it is unwise to speculate on the wider implications of this work. However, those who advocate creative design as the key to approaching the study of living things may wish to contribute at least one thought. The more we study bacteria and other single-celled life forms, the more sophisticated we find them to be. Simple mutations of the type under investigation do appear to be important for the long-term survival of these microscopic creatures. Consequently, if a complex mechanism for controlling mutations in bacteria exists, it should be recognised as a further evidence of intelligent design.
As far as evolutionary theory is concerned, these researches may lead to surprising conclusions. Some might suggest that they open the door to rapid evolutionary change, but this takes us way beyond the boundaries of empirical science. Everything we know about the complexity of any specific organ suggests that much more than a host of concurrent mutations is required to produce it!
It may be relevant that the mutations being studied are restoring an ability in the bacterium to manufacture food from specific nutrients. One hypothesis that seems worthy of exploration is that complex mechanisms exist for conserving genetic information whilst, at the same time, facilitating limited variability. This, after all, is the experience of the bacterium in Hall's laboratory!
We find these discoveries fascinating. Being somewhat dissatisfied with neoDarwinism, some biologists are finding ways of testing the predictions of the theory. If others join Hall in surprising the academic community, we may be coming to the end of an era. Theoretical biology may be emerging from years of stagnation and setting out on a new journey of exploration. If so, it is likely to have an exciting future!
David J. Tyler (1992)
