Abstract
George Shull’s 1908 seminal article ‘The composition of a field of maize’ marked the ‘exploitation of heterosis in plant breeding, surely one of genetics’ greatest triumphs’. Hybrid corn became a ‘symbol of American agriculture’ and ‘the paradigm for all developments of \(\hbox {F}_{1}\) hybrid crop varieties and more generally breeding. But there is still no consensus on the definition of heterosis while its biological basis, causal factors and genetic mechanisms remain ‘unknown’, or at best ‘poorly understood’. It is thus logical to reverse the usual approach from the exploitation of a mysterious heterosis to the triumph of hybrid corn and focus on what breeders and geneticists do rather than on the theoretical reasons for their success. This factual approach produces surprising results: (i) hybrid corn extends the isolation technique of autogamous cereals to the allogamous maize; (ii) a ‘hybrid’ is an ordinary corn plant made reproducible by the breeder and only the breeder. It is proprietary rather than ‘hybrid’; (iii) for all practical purposes, heterosis is irrelevant; (iv) Shull justified his ‘hybrid’ breeding method by the ad hoc argument of maize ‘hybrid vigour’ which in 1914, he conflated under the name of heterosis with Edward East’s concept of physiological stimulation due to heterozygosity; (v) hybrid corn can increase yield only once and by a small margin and (vi) the huge yield gains of the last 80 years came from mass selection, a process inconsistent with the theory of heterosis. In conclusion, the enduring success of ‘hybrid’ corn was achieved at the expense of farmers, common welfare and biodiversity and dovetails with the industrial agriculture requirements of crop uniformity and breeder monopoly over reproduction. This critical understanding of the paradigm of plant breeding could have important implications for breeders and geneticists.
Similar content being viewed by others
References
Beal W. 1876 Rept. Michigan State Board Agric. 15, 212–213
Beal W. 1880 Rept. Michigan State Board of Agric. 19, 287–288.
Bruce A. 1910 The Mendelian theory of heredity and the augmentation of vigor. Science 827, 627–628.
CIMMYT 1997 Book of abstracts. The genetics and exploitations of heterosis in crops; an international symposium. CIMMYT, Mexico.
Comstock R. 1964 Selection procedures in corn improvement. Proceedings of the 19th Annual Hybrid Corn Industry Research Conference 1964, pp. 1–8.
Comstock R., Robinson H. and Harvey P. 1949 A breeding procedure designed to make maximum use of both general and specific combining ability. Agron. J. 41, 360–367.
Coors J. G. 1997 Selection methodologies and heterosis. In CIMMYT op. cit., p. 170.
Crabb R. 1947 The hybrid corn makers, prophets of plenty. Rutgers University Press, New Brunswick.
Crow J. 1998 90 years ago: the beginning of hybrid maize. Genetics 148, 923–928.
Crow J. 2001 Plant breeding giants: Burbank, the artist; Vavilov, the scientist. Genetics 158, 1391–1395.
De Vries H. 1907 Plant-breeding, comments on the experiments of Nilsson and Burbank. The Open Court Publishing, Chicago.
Duvick D. Heterosis: feeding people and protecting natural resources. In CIMMYT op. cit., pp. 6–7.
Duvick D. 2001 Biotechnology in the 1930s: the development of hybrid maize. Nat. Rev. Genet. 2, 69–74.
East E. 1909 The distinction between development and heredity in inbreeding. Am. Nat. 43, 173–181.
East E. 1936 Heterosis. Genetics 21, 375–397.
Fisher R. 1925 Statistical methods for the research worker. Oliver and Boyd, Edinburgh.
Fisher R. 1949 The theory of inbreeding. Oliver and Boyd, Edinburgh.
Goldman I. Inbreeding and outbreeding in the development of a modern heterosis concept. In CIMMYT op. cit., pp. 4–5.
Hallauer R. Heterosis: what we have learned, what have we done, and where are we headed? In CIMMYT op. cit., pp. 345–347.
Hayes H. 1963 A professor’s story of hybrid corn. Burgess Publishing Company, Minneapolis.
Hull F. 1952 Recurrent selection and overdominance. In Heterosis, a record of researches directed toward explaining and utilizing the vigor of hybrids (ed. J. W. Gowen), pp. 451–473. Iowa State College, Ames.
Jones D. F. 1918 The effect of inbreeding and cross breeding upon development. Conn. Expt. Sta. Bull. 207.
Jones D. 1919 Inbreeding in corn improvement. Breeder’s Gazette, May 8, pp. 1113; May 15, p. 1182; May 22, p. 1214.
Jones D. 1919 Hybrid vigor and its meaning. Sci. Am. 121, 230–231.
Jones D. 1944 Biographical memoir of Edward Murray East (1879–1938). US Natl. Acad. Sci., Biog. Memoirs XXXIII, ninth memoir.
Keeble F and Pellew C. 1910 The mode of inheritance of stature and of time of flowering in peas (Pisum sativum). J. Genet. 1, 47–56.
Le Couteur J. 1836 On the varieties, properties, and classification of wheat. W. J. Johnson, London.
Lewontin R. and Berlan J-P. 1990 The political economy of agricultural research. In Agroecology. (ed. R. C. Carroll, J. H. Vandermeer and P. M. Rosset), pp. 613–628. McGraw-Hill, New York.
Mangelsdorf P. 1951 Hybrid corn. Sci. Am. 185, 39–47.
Mangelsdorf P. 1952 Gene interaction in heterosis. In Heterosis (ed. J. W. Gowen), pp. 320–329. Iowa State College, Ames.
Mangelsdorf P. 1955 George Harrison Shull. Genetics 40, 1–4.
McLean S. D., Vasal S. K., Pandey S. and Srinivasan G. The use of testers to exploit heterosis in tropical maize at CIMMYT. In CIMMYT op. cit., pp. 26-27.
Moll R., Lindsey M. and Robinson H. 1964 Estimates of genetic variances and level of dominance in maize. Genetics 49, 411–423.
Pickett A. and Galvey N. 1997 A further evaluation of hybrid wheat. Plant Var. Seeds 10, 15–32.
Schrödinger E. 1952 Are there quantum jumps? Brit. J. Phil. Sc. 3, 109–123. (Schrödinger quotes B. Farrington, 1949 Greek Science, 2, pp. 273. Pelican Books, London).
Shull G. 1908 The composition of a field of maize. Am. Breeders’ Assoc. Rep. IV, 296–301.
Shull G. 1909a A pure-line method in corn breeding. Am. Breeders’ Assoc. Rep. V, 51–59.
Shull G. 1909b Hybridization methods in corn breeding. Am. Breeders’ Assoc. Rep. VI, 63–75.
Shull G. 1910 The genotype of maize. Am. Nat. 45, 234-252.
Shull G. 1948 What is ‘heterosis’? Genetics 33, 439–446.
Shull G. 1952 Beginnings of the heterosis concept. In Heterosis (ed. J. W. Gowen), pp. 14–48. Iowa State College, Ames.
Sprague G. 1955 Corn breeding. In Corn and corn improvement (ed. G. Sprague), pp. 221–291. Academic Press, New York.
Sprague G. and Eberhart S. 1977 Corn Breeding. In Corn and corn improvement (ed. G. Sprague), pp. 305–362. Am. Soc. of Agron., Madison, WI.
Stuber C. The biology and physiology of heterosis. In CIMMYT op. cit., pp. 108–109.
Tsaftaris A. S., Kafka M., Polidoros A. and Tani E. 1997 Epigenetic changes in maize DNA and heterosis. In CIMMYT op. cit., pp. 112–113.
Welch F. 1961 Hybrid corn: a symbol of American agriculture. Am. Seed. Trade. Assoc. 16th hybrid corn industry research conference, pp. 95–99.
Acknowledgements
What were mere intuitions about ‘hybrid’ corn took shape in the intellectually ebullient atmosphere of Richard Lewontin’s laboratory where I learned that even technical genetic issues should be cast in their proper social, epistemological, historical and political framework and where Diane Paul introduced me to the field of history of science. Her sharp mind was decisive from the early stages to the completion of this article. Both declined to co-author it although it is also theirs. I am grateful to the reviewers of the Journal of Genetics for their suggestions.
Author information
Authors and Affiliations
Corresponding author
Additional information
Corresponding editor: Arun Joshi
Appendices
Appendix
Vocabulary matters
The word ‘hybrid’ (from Latin ibridus, of mixed blood and Greek hubris, exuberance, excess) implies a positive effect of crossing on vigour. The 19th century biologists made the distinction between hybridization and crossing. The mule mixing the ‘blood’ and strength of the horse with the blood and rusticity of the ass is a hybrid.
‘In a broad sense, wrote Paul Mangelsdorf in Scientific American (1951, p. 39) all corn is hybrid for this plant is a cross-pollinated species in which hybridization between varieties and between races occur constantly. (...)’
A ‘hybrid’, then, is an ordinary corn plant. Mangelsdorf evades the issue with the claim:
‘But the hybrid corn with which we shall deal here is a planned exploitation of this natural tendency on a scale far beyond that possible in nature.’
He then goes on: ‘The biological basis of hybrid corn is a genetic phenomenon known as ‘hybrid vigour.
No! The biological basis of ‘hybrid’ corn is natural variations made reproducible by crossing pure lines. The incantatory use of ‘hybrid’, ‘hybridization’, ‘natural tendency (to hybridize)’ misleads users and readers.
Moreover, ‘hybrid’ conflates the process of making ‘hybrids’ (‘hybridizing’ – crossing!) pure lines with the biological result: heterozygous quasi clone or to simplify heterozygous clone if we deal with the biological aspect, or proprietary clone if we focus on the anthropological dimension of turning life into a commodity. James Crow’s observation derived from Ronald Fisher (1949) that hybridization is the ‘equivalent of reproducing asexually (my italics) the best individual of a segregating population’, i.e. cloning, legitimates extending the term ‘clone’ (Crow 1998) to the legally ‘homogeneous and stable’ crops of industrial agriculture.
Dolly extended cloning to mammals. Cloning reflects the two century long drive for uniformity, standardization and normalization required by the mass production of an industrial society. It also reflects the secular struggle against the free reproduction of living organisms. No property rights over varieties are possible because they are heterogeneous and changing while clones, being ‘fixed’, can be protected and patented. Modern industrial clones contrast with peasant land races or varieties (which have the character of being varied, the opposite of uniformity) produced by mass selection that has created since the beginnings of agriculture the immense wealth of cultivated biodiversity that is now in jeopardy.
Rights and permissions
About this article
Cite this article
Berlan, JP. Hybrid corn and the unsettled question of heterosis. J Genet 97, 1075–1082 (2018). https://doi.org/10.1007/s12041-018-1037-2
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s12041-018-1037-2