Nearly eighty years ago, my father, William Bateson, be-came fascinated by the phenomena of symmetry and metameric regularity as exhibited in the morphology of animals and plants. It is difficult today to define precisely what he was after, but, broadly, it is clear that he believed that an entirely new concept of the nature of living things would develop from the study of such phenomena. He held, no doubt correctly, that natural selection could not be the only determinant of the direction of evolutionary change and that the genesis of variation could not be a random matter. He therefore set out to demonstrate regularity and "lawfulness" among the phenomena of variability.
In his attempt to demonstrate a sort of order which the biologists of his day had largely ignored, he was guided by the notion, never clearly formulated, that the place to look for regularity in variation would be precisely where variation had its impact upon what was already regular and repetitive. The phenomena of symmetry and metamerism, themselves strikingly regular, must surely have been brought about by regularities or "laws" within the evolutionary process and, therefore, the variations of symmetry and metamerism should precisely exemplify these laws at work.
In the language of today, we might say that he was groping for those orderly characteristics of living things which illustrate the fact that organisms evolve and develop with-in cybernetic, organizational, and other communicational limitations.
It was for this study that he coined the word "genetics."152
He set out to examine the material in the world's museums, private collections, and journals bearing upon the teratology of animal symmetry and metamerism. The de-tails of this survey were published in a large book153 which is still of considerable interest.
To demonstrate regularity within the field of teratological variation, he attempted a classification of the various sorts of modification that he encountered. With this classification I am not here concerned, except that in the survey he happened upon a generalization which can be called a "discovery." This discovery came to be called "Bateson's Rule" and remains one of the unexplained mysteries of biology.
The purpose of the present note is to place Bateson's Rule in a new theoretical perspective determined by cybernetics, information theory, and the like.
* This essay has been accepted for publication in the Journal of Genetics, and is here reproduced with the permission of that journal.
152 !W. Bateson, "The Progress of Genetic Research," In-augural Address, Royal Horticultural Society Report, 1906.
153 W. Bateson, Materials for the Study of Variation, London, Macmillan and Co., 1894.
Briefly, Bateson's Rule asserts in its simplest form that when an asymmetrical lateral appendage (e.g., a right hand) is reduplicated, the resulting reduplicated limb will be bilaterally symmetrical, consisting of two parts each a mirror image of the other and so placed that a plane of symmetry could be imagined between them.
He himself was, however, very doubtful whether such simple reduplication ever occurs. He believed and accumulated evidence to show that, in a very large proportion of such cases, one component of the reduplicated system was it-self double. He asserted that in such systems the three components are normally in one plane; that the two components of the doublet are mirror images of each other; and that that component of the doublet which is the nearer to the primary appendage is a mirror image of the primary.
This generalization was shown by my father to hold for a very large number of examples of reduplication in the vertebrates and in arthropods, and for a few cases in other phyla where the museum material was, of course, more scarce.
Ross Harrison154 believed that Bateson underestimated the importance of simple reduplication.
Whether or not simple reduplication is a real and common phenomenon, I shall begin this essay with a discussion of the logical problems which it would present.
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