CORRESPONDENCE approach to the problems of development, ageing and cancer. I have no doubt that Darwinism not tautological Hinshelwood will one day be placed on the SIR - I would question both the ability and logical. Attempts to avoid the tautology by same high level as Luria for his contribution the need of Torres's work' to defend the redefining "fitness" can succeed only by to our understanding of the living state. theory of natural selection from the accusa­ making the phrase false as well as falsifiable. HARRY RuBIN tion of tautology2. Torres presents a novel This, however, does not imperil the scien­ University of California, Berkeley, example of an evolutionary optimization tific status of Darwin's theory of evolution Department of Molecular model\ in which the 'instantaneous fitness' using natural selection. Darwin claimed, and Cell Biology, of a set of phenotypic variants (in this case first, that evolution had occurred and, sec­ 229 Stanley Hall, metabolic pathways) is defined according to ond, that natural selection was the mechan­ Berkeley, California 94 720, USA a set of plausible rules (in this case thermo­ ism responsible. Both of these propositions 1. Watson, J.D. Nature350, 113 (1991). dynamic criteria). All such models stand or are testable and falsifiable and therefore 2. Dean, A. C. R. & Hinshelwood, C. Nature 199, 7-11 fall on how well they predict the reality found scientific. (1963). 3. Dean, A. C. R. & Hinshelwood, C. Growth, Function and in nature. If there is an anomaly, the model is CoEL HELLIER Regulation in Bacterial Cells (Oxford University Press, modified a posteriori, by changing the Mullard Space Science Laboratory, 1966). 4. Sonneborn, T. Adv. Genet.1, 263-358 (1947). criteria, by introducing constraints to the University College London, 5. Meins, F. Jr & Binns, A. Proc. natn. Acad. Sci. U.S.A. 74, phenotype set or by adding criteria from Holmbury StMary, Dorking, 2928-2932 (1977). other models (for example, sexual selection Surrey RH5 6NT, UK 6. Fox, M. & Radicic, M. Mutat. Res. 49,275-296 (1978). 7. Harris, M. Cell, 29,483-492 (1982). criteria that result in traits being far from 8. Rubin, A. L., Yao, A. & Rubin, H. Proc. natn. Acad. Sci. U.S.A. thermodynamically efficient in terms of indi­ 87, 482-486 (1990). vidual survival). Thus, it can be argued, call­ Hinshelwood in ing a phenotype 'instantaneously fit' equates to saying that it is there in the first place, and the Pantheon? Novel reading so we are back to the original tautology: 'sur­ SIR- James D. Watson's obituary of Luria 1 SIR - Steven Henikoff and Robert Levis vival of the survivors'. was a fitting tribute to a pioneer of molecular (Nature 350, 9; 1991) suggest that the use of The tautology argument is nevertheless biology. There is no doubt that the the word 'novel' in the biomedical literature flawed because, as many evolutionists since Luria-Delbruck fluctuation test played a is growing dramatically. Although this seems Darwin have reiterated, natural selection crucial role in establishing the spontaneous indeed to be the case, they do not look into emerges as an inevitable consequence of ob­ nature of mutations in bacteria, and made possible explanations for this increase. As served facts and empirically derived pre­ bacteria the organisms of choice for studying 'novel' means 'of a new kind; different from cepts. To deny the existence of natural selec­ the nature of the gene. anything seen or known before', its use is cer­ tion, therefore, is to deny that organisms de­ However, contrary to Watson's remark, tainly justifiable on occasion, and may often pend on limited resources for their survival, Cyril Hinshelwood did not argue against the be preferable to words such as 'unique', that they reproduce with heritable variation, mutational origin of resistant bacteria. which presupposes that no other examples and that this variation will affect their ability Instead, he said there was another way they will subsequently be found, or 'brand new', to exploit those resources. It is worth noting could become resistant, that is, through a which suggests that it did not exist before its that Popper no longer considers natural change in their reaction pattern or chemical discovery. 'Somewhat atypical' might often 4 selection to be tautological , although he still equilibrium. This he and his co-workers at be more accurate, but with journals setting considers it to be a "metaphysical research Oxford established on the basis of the speed limits on title and abstract length, 'novel' has program" in that to assume natural selection of change, the large fraction of the popula­ an edge in being only five characters rather accounts for all evolutionary history (to the tion involved, the finely graded nature of the than 17. exclusion of other mechanisms) is more or response, the lack of precise specificity and The increased use of 'novel' may also be 2 3 less unfalsifiable. So far, however, no alter­ the reversibility of the altered state • . exaggerated in certain fields. From January native fact-based mechanism is known that Unfortunately, the work of the Oxford 1989 to March 1991, only 1.1 per cent of all also accounts for the exquisite adaptation of group coincided with the beginnings of the Medline citations use the word 'novel', but organisms to their environment. remarkable development of molecular gen­ 3.5 per cent of citations on HIV (human etics, and it seemed irrelevant at the time, immunodeficiency virus) claim novelty. Al­ MICHAEL E. WEALE Department of Biology, particularly because the changes could not though HIV papers for the same period University of Southampton, be identified with any macromolecule, in make up 2.3 per cent ofthe citations, 7.2 per Bassett Crescent East, contrast to the elegant simplicity of genetic cent of the 'novel' papers are on HIV. Given Southampton S09 3TU, UK change. that there are now over 60,000 papers on Closer inspection shows that the adaptive HIV catalogued in Medline (nearly seven changes described by the Oxford group were papers per nucleotide pair), it is difficult to 1. Torres, J.-L. II Nuovo Cimento 130, 177 (1991). 2. Maddox, J. Nature350, 653 (1991). analogous to the Dauermodifikationen of believe that another few hundred novel dis­ 3. Parker, G. A. & Maynard Sm1th, J. Nature 348, 27-33 Paramecium described by Jollos and con­ coveries will be made each year. This brings (1990). 4 4. Popper, K. R. Dialectica32. 339-355 (1978). firmed by Sonneborn • Similar findings have up another question: if an organism needs since been made in plant5 and animal cell only n nucleotide pairs completely to de­ 6 8 SIR-John Maddox has raised once again the culture - , and appear to be central to the scribe itself, then how many papers are re­ "nagging doubt" that the "theory of natural processes of differentiation and neoplastic quired fully to understand the organism? selection" is tautological. This is easily transformation. Indeed, the adaptive Even the venerable bacteriophage T4 (which resolved once it is realized that natural selec­ changes of large cell populations may well be many people seem to think is 'solved') can tion is a mechanism, not a theory. In a system the most common heritable changes they claim only 1,226 citations (0.007 per nucleo­ of replication with mutation, natural selec­ undergo, if we accept an inheritance that tide pair) in the entire Medline database tion must occur. This is why Darwin called it persists for many generations upon removal since 1966. "natural" selection, meaning "tautologically of the inducing constraint, but is subject to ALAN c. CHRISTENSEN entailed" selection. The phrase "survival of gradual reversal. Department of Biochemistry and the fittest" was introduced merely as an illus­ Thus, while molecular genetics flourished Molecular Biology, tration for those who misunderstood the as a result of Luria's work, adaptive change Thomas Jefferson University, term natural selection, and is equally tauto- languished, resulting m a one-sided Philadelphia, Pennsylvania 19107, USA 600 NATURE · VOL 351 · 20 JUNE 1991 © 1991 Nature Publishing Group.