TEISSIER, GEORGES

(b. Paris, France, 19 February 1900; d. Roscoff, France, 7 January 1972)

zoology, population genetics.

A field naturalist from childhood, Teissier took an early interest in mathematics. When he was admitted to the École Normale Supérieure in 1919, he was accepted in the mathematics section, not that of natural sciences. Throughout his life there were three aspects to his scientific activity: zoology, biometrics, and population genetics. These interests are shown not only in his scientific articles but also in the orientations of his students. In 1945 he was appointed professor of zoology at the Sorbonne and director of the Biological Center at Roscoff in Brittany. He hated scientific meetings and traveling and spent most of his time in Paris and Roscoff. Characterized by an inexorable logical rigor and a notable erudition, he was very abrupt and rarely encouraging; nevertheless, he succeeded in training many young scientists who are now internationally known. This rigor, which was expressed in his public life as well as in his scientific activity, had family roots. His parents, who were schoolteachers, belonged to the rigidly moral Calvinist community of southern France, a group that had been persecuted in the seventeenth and eighteenth centuries. Although an agnostic, Teissier possessed many Calvinist attitudes.

During World War II Teissier was a member of the French Resistance from 1941 and organized resistance activities at the Sorbonne. He then joined the Francs Tireurs et Partisans resistance group, succeeding Marcel Prenant (a fellow professor) at headquarters when Prenant was arrested and deported by the Nazis. In 1945 after the liberation of France, Teissier contributed to the development of scientific research and to the training of young scientists as deputy director, and then director, of the newly formed Centre National de la Recherche Scientifique (CNRS), where he succeeded Frédéric Joliot-Curie. It was at this time that he set up the Laboratoire de Génétique Evolutive at Gif-sur-Yvette (director, 1951–1965). He was obliged to leave his post at the CNRS in 1950 for political reasons. Throughout this period he played an important role, together with Boris Ephrussi and Philippe L’Héritier, in establishing a genetics course at the Sorbonne.

Author of more than 175 publications and a member of the Académie des Sciences, Teissier’s main interests were Cnidaria, growth, and population genetics.

Cnidaria. From 1920 on, Teissier had a particular interest in marine biology. He wrote several articles on the growth of hydrozoans and other Cnidaria. He showed that the eggs of hydroids are anisotropic and described their early polarity and the persisting polarity of embryo fragments during regulation following experimental fragmentation (1931). With Bertil Swedmark he published descriptions of several Cnidaria of the littoral interstitial meiofauna and established the order Actinulida for these newly described organisms (1966).

Growth and Biometrics In 1927 Teissier began his studies of animal growth. He rapidly became aware that quantitative methods were necessary, a view not widely accepted at the time. He increasingly adopted biometrical methods and became a statistician.

His dissertation (1931) was devoted to insects, in particular the flour beetle, Tenebrio molitor, and the honeycomb moth, Galleria mellonella. The size of an arthropod increases at each molt. At each step, the form and structure change. These changes can be expressed quantitatively by comparing the growth rate of the organ under study at each molt with an overall logarithmic body measure used as a reference. The relative growth rates of the different organs are represented by curves: if the studied organ grows more rapidly than the overall measure, the slope is greater than 1. If growth takes place less rapidly in the organ under investigation, the slope is less than 1. The same mathematical relationship was discovered independently by J. S. Huxley. The two men agreed to describe this phenomenon as an “allometric relationship” (1936). The practical importance of this law and its general applicability were quickly shown for both crustaceans and insects.

In the crustacean Maia squinado, growth consists of three distinct stages separated by two critical molts. These are clearly shown in Figure 1. The laws of growth, shown for the first time in this study, are applicable to both animals and plants. Their general applicability has made them particularly useful in the study of chemical embryology and in endocrinology. For example, by studying changes in the slope of curves on this kind of graph, Hélène Charniaux-Cotton was able to show the existence

of a gland responsible for secondary sexual characters in crustaceans.

A more intensive study of sexual variants enabled Teissier to develop a method for correlational factor analysis and for analysis of principal components (1938). Along with experimental studies of growth, he carried out a series of theoretical studies with René Lambert that revealed the existence of a “biological similarity” and showed the variation of a number of biological rhythms with size (1927).

Evolutionary Genetics Teissier’s interest in mathematics led him to population genetics. In 1932, at a time when Darwinism was of only peripheral interest in France, he began a series of studies on Drosophila populations with Philippe L’Héritier. At this stage, population genetics—which had originated a dozen years before under the inspiration of J. B. S. Haldane and R. A. Fisher in England and Sewall Wright in America—was still largely theoretical. The main project of population geneticists was to give a mathematical expression to the changes in allelic and genotypic frequencies from one generation to another, given the existence of certain parameters. But no experimental study had yet been carried out.

Drosophila melanogaster, whose genetics were already well known, seemed to be the ideal subject. L’Héritier and Teissier set up population cages that allowed populations of 2,000 to 3,000 flies to be followed over a period of months or years, under conditions of severe food competition (1933). These cages, which are still used throughout the world, enabled many discoveries to be made.

By placing two isogenic strains that differed by only one mutation (such as Bar and Wild-type or Sepia and Wild-type) in a cage, they were able to make direct measurements of changes in allelic and genotypic frequencies during competition and to calculate the selective value of the different genotypes. The experimental model could then be used to test various theoretical models for reliability and to suggest possible modifications.

Whichever gene is studied, the replacement of normal mutant individuals by normal flies initially takes place very rapidly. However, the rate of change soon declines, and after several months, changes in the proportions of the two alleles take place extremely slowly. The frequency of the mutant gene may be so low that it can disappear completely, by chance; for other mutations a quasi-stable situation may be reached while the mutation is still relatively frequent (1937). In such cases it seems that natural selection, resulting from food competition, tends to maintain the two alleles in stable proportions.

The genetic basis of the situation described by Darwin for natural populations was thus established. Such balanced polymorphisms, described in natural populations of Drosophila pseudoobscura by Theodosius Dobzhansky, are now universally considered to be an indispensable condition for the evolutionary process. The maintenance of such polymorphisms despite the existence of selection may seem somewhat paradoxical. This problem led to a series of studies to explain the manner in which polymorphisms are maintained. The most straightforward hypothesis suggests that the three genotypes do not have the same adaptive value, with heterozygotic individuals producing more offspring on average than the two homozygotic types. This hypothesis is difficult to test when one of the alleles is completely recessive and the heterozygotes cannot be distinguished from the dominant homozygotes. Where only two genotypes are involved and one of the homozygotes is inviable, such a study is clear-cut. Using this procedure, Teissier showed the possibility of maintaining a lethal gene and a viable allele in high, stable frequencies in an experimental population (1942). The observed equilibrium occurs at exactly the level predicted theoretically, given experimental differences in fecundity between strains. These results led to an exhaustive theoretical study of the equilibria shown by lethal genes (1944).

Another way in which polymorphisms may be maintained was revealed in a study of competition between Bar and Sepia mutants and their wild–type alleles. An abnormally slow decline in the elimination of the mutant strains was coupled with an increase in the selective value of Bar mutants when they were only in competition with normal larvae (1934). This phenomenon, which had been predicted theoretically but never shown to exist, has since been studied by a number of authors and probably plays an important role in maintaining polymorphisms.

Another line of research was opened up by the discovery of a fixed mutant—later discovered to be Sepia—in a natural population. This strain had a consistent frequency of around 0.22 (1943). Given that mutations are normally eliminated, this discovery was of obvious interest. Its presence suggested that the adaptive value of a mutant depends not only upon the mutation itself but also upon the genetic background in which it is found. This hypothesis was confirmed by a series of experimental results (1947). Although this conclusion may seem obvious today, at the time it was revolutionary, raising the problem of interactions within the individual’s genome, which has been the subject of much study since Teissier’s discovery. Besides these particularly original studies, Teissier carried out a series of important collaborative investigations into genetic polymorphisms in natural populations of the crustacean Spaheroma serratuin (1960).

Teissier was an important early figure in the field of biometrics and population genetics. However, the isolation of France during World War II—at a time when these subjects were really beginning to take off—together with the fact that although Teissier wrote many articles, he did not produce any book synthesizing his ideas and approach, limited his scientific impact, despite the importance of many of his discoveries.

BIBLIOGRAPHY

I. Original Works. “Théorie de la similitude biologique”, in Annales de physique et de physico chimie biologique, 3 (1927), 212-246, written with René Lambert; “Étude expériementale du développement de quelques Hydraires”, in Annales de science naturelle, sér. zoologique, 10th ser., 14 (1931), 5-59; “Recherches morphologiques et physiologiques sur la croissance des Insectes”, in Travaux de la station biologique de Roscoff, 9 (1931), 29-238; “Étude d’ une population de Drosophiles en équilibre,” in Comptes rendus de l’Académie des sciences, 197 (1933), 1765–1767, written with Philippe L’Héritier; “Une expérience de sélection naturelle. Courbe d’élimination du gène ‘bar’ dans une population de Drosophiles en équilibre,” in Comptes rendus de la Société de biologie, 117 (1934), 1049–1051, written with Philippe L’Héritier; “Croissance des variants sexuels chez Maia squinado” in Travaux de la station biologique de Roscoff, 13 (1935), 91–130; “Terminologie et notation dans la description de la croissance relative,” in Comptes rendus de la Société de biologie, 121 (1936), 934–936, written with J. S. Huxley; “Elimination des formes mutantes dans les populations de Drosophiles. I Cas des Drosophiles ‘bar,’” ibid., 124 (1937) 882–884, written with Philippe L’Héritier; “Elimination des formes mutantes dans les populations de Drosophiles. II . Cas des Drosophiles ‘ebony,’” ibid., 884–886, written with Philippe L’Héritier; “Un essai d’analyse factorielle. Les variants sexuels de Maia squinado,” in Bio-typologie, 7 (1938), 73–96; “Persistance d‘un gène léthal dans une population de Drosophiles,” in Comptes rendus de l’Académie des sciences, 214 (1942), 261–263; “Apparition et fixation d’un gène mutant dans une population stationnaire de Drosophiles,” ibid., 216 (1943), 88–90; “Équilibre des gènes léthaux dans les populations stationnaries panmictiques,” in Revue scientifique, 82 (1944) 145–159; “Mécanismes de l’évolution,” in La pensée, 2 (1945), 5–19 and 3 (1945), 15–31; “Variation de la fréquence du gènes ebony dans une population stationnaite de Drosophiles,” in Comptes rendus de l’Académie des sciences, 224 (1947), 1788–1789; “L‘évolution du patrimoine héréditarie dans les populations naturelles,” in La progenèse (Centre International de I’Enfance, Travaux et Documents), 8 (1955), 57–85; “Génétique des populations de Sphareoma serratum (F.),” in Cahiers de biologie marine, 1 (1960), 103–111, 221–230, 279–293, and 6 (1965), 195–200, written with Charles Bocquest and Robert Lejuez; and “ The Actinulida and Their Evolutionary Significance” in the Cnidaria and Their Evolution. Symposia of the Zoological Society of London, 16 (London, 1966), 119–134, written with Bertil Swedmark.

Claudine Petit