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CYTOPLASMIC HERETICS JAN SAPP* When Julian Huxley wrote Evolution: The Modern Synthesis (1942), research on cytoplasmic inheritance and symbiosis were disregarded [I]. What torch-bearers called "the evolutionary synthesis" was based on a merger of natural selection with Mendelian gene mutations and recombination [2]. Today, the view that gene mutations and recombination (and particularly chromosomal genes) are responsible for evolutionary variation is as pervasive in the teaching of biology as it is in popular accounts of genetics. It has also been bolstered by a plethora of historical studies of the development of the chromosome theory from Drosophila to DNA. Certainly, there were plenty of protests on the road to the major genetic synthesis. To account for those individuals, disciplines, or scientific nations standing in opposition, historians generally searched for ideological, philosophical , or institutional faults which interfered with the progress ofreason. This approach seemed well-grounded for those inspired with the belief that chromosomal genes were indeed the sole basis of heredity. And this perspective was hardened in the dark shadow of Lysenkoism and the chill of the Cold War. But not all protests could be so easily explained. The inheritance of cytoplasmic sub-microscopic particles, cytologically visible structures and patterns, and self-perpetuating metabolic states, have been discussed and investigated by various groups of biologists throughout the 20th century [3]. Yet, such studies have been carried out close to the margins of, and developed in constant tension with, the dominant research programs and doctrines of Mendelian genetics. Cytoplasmic inheritance has been either rejected or trivialized as "exceptions" by leading geneticists . T. H. Morgan wrote in 1926, "Except for the rare cases of plastid inheritance all known characters can be sufficiently accounted for by the presence of genes in the chromosomes. In a word, the cytoplasm may be The author wishes to thankJoshua Lederberg and Art Forer for discussions about several aspects of this essay. Along with the reviewers, they also offered helpful suggestions. *Department of Biology, York University, 4700 Keele Street, North York, Ontario, Canada M3J 1P3.© 1998 by The University of Chicago. All rights reserved. 0031-5982/98/4102-1053$01.00 224 Sapp ¦ Cytoplasmic Heretics ignored genetically" [4]. George Beadle extended the dogma of the modern genetic synthesis into the realm of microbial biochemical genetics when he argued in 1949: In view of the elaborate mechanisms of mitosis and meiosis, which have evolved and persisted throughout almost the whole of the plant and animal kingdom and which evidendy have a great selective advantage, it would be most remarkable if the cytoplasm could compete as a carrier and transmitter of hereditary units in any except a few very special circumstances. [5] The universality of non-Mendelian heredity was not generally accepted by geneticists until the 1960s and early 70s, led by the research of Ruth Sager [6]. Today, geneticists are perfectly comfortable with mitochondria and chloroplast genomes. Cytoplasmic genes are no longer considered as "exceptions." These organelles have their own DNA, RNA, and ribosomes distinct from those of the nuclear chromosomes; they replicate and are typically transmitted from generation to generation maternally, through the egg cytoplasm. Morgan's dietim, once shared by many geneticists, no longer prevails. Nevertheless, two other issues still have a somewhat "exceptional " status in heredity and evolution. One concerns the inheritance of supramolecular structure and the role of the cell cortex in heredity and development. The other involves symbiosis in cell evolution and as a source of evolutionary change more generally. Both have often been discussed under the rubric of "cytoplasmic inheritance ," both pose challenges to neo-Darwinism, and both involve revisions of what is to count as an organism. Yet they have never been synthesized within a common explanatory framework. Indeed, as I will briefly review below, they evolved from within rhetorical paradigms of two divergent research traditions based on different questions, phenomena, and solutions. Moreover, at least as far as the origin of mitochondria and chloroplasts is concerned, evolution by symbiosis is a well-accepted idea. On the other hand, the inheritance of cytoplasmic structure is still often considered to be beyond the pale of contemporary biology. The Organism as a Whole At the end of the 20th century, we can still hear...

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