Heterosis and the future of animal improvement.

Abstract

HETEROSIS AND THE FUTURE OF ANIMAL IMPROVEMENT* I. MICHAEL LERNERf The target of this symposium is an important but ill-understood phenomenon, and the stated purpose for which we have been convened here is to review our current knowledge of it, to throw some light on its biological basis, and above all, to explore its potentialities for use in animal breeding. Heterosis is a subject which has been continuously discussed in the 20 or so years since the first major compilation of papers specifically devoted to it [1] appeared. In the last several volumes of Animal Breeding A bstracts, references on heterosis include a great number of review articles and books in many languages. Its molecular foundations , some of which have been anticipated by Haldane [2, 3], have recently been subjected to a thorough examination [4], Its application in plant and animal breeding has been widespread. Examples of its occurrence in natural populations and in domesticated species are numerous. Evidence for its existence predates by many decades or even centuries the invention of the term, and experimental investigations in a more or less methodical manner have been carried out on it for considerably more than half a century. And, of course, in its broad sense, heterosis was not unknown territory to Darwin and to generations of breeders before him. Yet it is fair to say that (1) there is no general agreement as to the precise meaning of the term, (2) there are many theories and ideas about the biological basis of heterosis but only a few hard facts, and (3) there is no proof that methods of animal improvement purporting * Presented at the Symposium on Heterosis held by the Polish Academy of Sciences in Warsaw, Poland, and arranged by the Institute of Genetics and Animal Breeding at Jastrzebiec, September 27-October 2, 1971. To be published in a Polish translation in the proceedings of the symposium. ? Department of Genetics and Institute for Personality Assessment and Research, University of California, Berkeley, California 94720. Perspectives in Biology and Medicine · Summer 1973 | 581 to utilize it are, indeed, optimal for all species in all situations. Even in corn production, where crosses between inbred lines are beginning to enjoy a worldwide monopoly, it has by no means been established unequivocally that breeding for heterotic performance is operationally the soundest procedure to follow. These are matters sufficiently well known not to require elaboration on my part. In any case, I shall assume that their features relevant to our collective task here will be covered by others with more competence and knowledge of biological and practical detail than I possess. Since I have no new experimental data, or any novel hypothesis to account for heterosis, or any fresh theoretical concepts to place before you, the question as to what I am doing here is obviously highly pertinent. Yet it is possible that I may have a minor contribution to make to this meeting. It will not be based on my previously published discussion of genetic homeostasis [5] to which I probably owe my presence here. Nor will it relate to my book on selection [6], which I am happy to note may be known not only to those of you at home with the English language but also to those who can read it with better comprehension than I can in its Polish translation. Rather, the gist of my remarks will be an extension of the considerations that governed Professor Hugh Donald and myself when we embarked on our attempt to discuss animal breeding in a broad social context [7]. Again, I am pleased to record that this work, true enough in a somewhat mutated form mostly as a result of deletions but in part because of changes in the course of transcription, is available in Russian, a language with which I together with others here can claim some familiarity. With this volume as a starting point, I want, by discussing some general problems and issues stemming from what may be flatteringly described as philosophical and social points of view, to provide a somewhat vaguely stated footnote to our proceedings here. Heterosis in Scientific Literature I do not feel compelled to survey the vast literature...