The conceptual framework resulting from the efforts of ‘developmental mechanics’ researchers in the late nineteenth century included a number of central assumptions that most were aware of and agreed upon. Cells were considered as the semi-autonomous modules of tissues and organs; within cells, the nucleus carried hereditary (genetic) information on which the cytoplasm is able to exert its influence. The cytoplasm of the egg and blastomeres contained ‘formative substances’ that, acting on hereditary information, would determine the differentiative fate of a cell. The distribution of these formative substances in the egg, through the process of early embryonic cell divisions (cleavage) would result in blastomeres equipped with different substances, thereby adopting different fates: this then resulted in what Roux called ‘mosaic development’. On the other hand, as shown in numerous experiments, embryos were able to ‘regulate’: a two-cell sea urchin embryo in which one blastomere is removed would still give rise to a complete larva, implying that the fate of cells is not irrevocably fixed, and that cells interact in complex manners to sort out where to move, how to arrange in space, and what shape and function (cell type) to adopt. Differences among workers in the field existed, and controversies arose, in terms of which of these phenomena (e.g. intrinsic determination vs regulation) plays a more important role, for a given embryo species and developmental stage, the intrinsic state of determination (‘Roux school’) or the power of regulation (‘Driesch school’). Differences also existed regarding the specific scientific goal, and the methodologies used to attain this goal, as well as the ‘scientific style’ of the researcher in question: there were those drawn to microscopy and cytology/histology in order to learn more details about the physical nature of the formative forces inherent in cells (e.g. T. Boveri or C. Herbst and their followers), whereas others were more interested in how the results of observations and experimental manipulations of embryos aligned with the ‘grand’ developmental puzzles of their day, such as mosaicism vs regulation, or variation/natural selection vs other alternative mechanisms underlying evolution. Many experimental approaches, including microsurgery on embryos (transplantation, implantation), the manipulation of abiotic factors (light, temperature, gravity) and the study of regeneration and teratogenesis, were initiated in this quest.

The Morgan group: studies of regeneration and experimental embryology

With almost no exception, ‘developmental mechanics of the first generation’ had learned their craft in the context of comparative embryology, and had rotated through a small number of research stations in Europe and the USA where this research could be conducted, notably the Zoological Station at Naples, Villefranche and Woods Hole. In these stations, specific ‘tables’ were reserved for (male) teams coming from different universities; later, special ‘woman tables’ were added. T.H. Morgan had worked and published on the development of sea spiders (Oppenheimer 1983). He (and many other developmental biologists) were swept up in the new wave of experimental embryology, and found himself closer to the ‘regulation school’ of thought. Most of the papers published in DGE by the Morgan group looked at regeneration in diverse species, from cnidarians, flatworms, echinoderms and arthropods to vertebrates. Cnidarians and flatworms, as well as echinoderms, had been known for more than 100 years for their amazing powers of regeneration, and Morgan and his first students (H. Randolph, F. Peebles, H.D. King) systematically explored how the exact location and orientation of the cut by which body parts were removed influenced the ensuing body pattern of the regenerate, and what rules could be deduced from the experimental outcomes.

A major technological advance came with the arrival of a new student, Nettie Stevens, who had been trained in histology at Stanford University (Carey et al. 2022). In Stevens’ papers (Stevens 1901, 1907, 1909a, b, 1910), as well as in all papers on regeneration from the Morgan group published after Stevens joined the lab, sections of the regenerates, treated with standard histological stains, were analyzed and documented. This allowed for much more insightful conclusions compared to the previous studies, in which regenerates were simply observed externally. For example, in her 1901 paper on Tubularia (Stevens 1901), she correctly identified, as one of the first, the origin and development of the blastema, which became so important for all studies in regeneration. As further discussed in a later section (see below), Stevens’ histological and cytological expertise also allowed her to identify the Y-chromosome in flies and other insects, and link it to the determination of male sex, which in turn convinced Morgan and others to associate genes with chromosomes, and to initiate the whole new field of classical genetics.

Other students (Annah Hazen, working on the sea anemone Sagartia (Hazen 1903); Margaret Reed and Esther Byrnes, working on limb regeneration in amphibians and crustaceans (Byrnes 1904; Reed 1903, 1904)) followed in Stevens’ footsteps and added histological detail to their analyses. The importance of this detail for the conceptual framework in which Morgan and other developmental mechanics researchers of the ‘regulation’ school operated can be gleaned from the ‘News and Views’ article he published on Margaret Reed’s data in 1904 (Morgan 1904). Reed had found that muscle, traditionally considered a mesodermally derived tissue, developed from ectoderm in the regenerating crustacean limb (Reed 1903, 1904). This implied that germ layers are not yet determined in their fate, supporting the pivotal function of regulation in development. It is reasonable to suppose that, in general, regeneration as a focus of study was very much ‘en vogue’ for the ‘regulationist’ school of researchers, since it revealed a great amount of plasticity in the response of tissues to different kinds of ablations.

Finally, we would like to mention that several co-workers of Morgan ‘dabbled in’ the techniques of subjecting embryos to different conditions (‘abiotic factors’), or techniques for analyzing the effects of ablating embryo parts on pattern formation. Following the discovery of lens induction by the optic cup (retinal primordium) in amphibians by H. Spemann (Spemann 1901), Helen D. King in the Morgan lab did similar experiments in Rana palustris, extirpating the eye primordium at different stages (King 1905). Her work mainly confirmed Spemann’s findings, but also concluded that the lens can (in some cases) develop without the presence of the optic cup, sparking a series of subsequent analyses (in other labs) that aimed at resolving this controversy. Anne Todd (Todd 1904) did lesion/ablation studies in the gastrulating frog embryo and carefully analyzed abnormalities in later patterns in the nervous system and other organs; she did however not notice results that would hint at the function of the dorsal blastopore lip (the ‘Spemann/Mangold organizer’; see further below). In a series of later studies, Georgina B. Spooner (Morgan and Spooner 1909), Ethel Nicholson Browne (Browne 1910) and Pauline Dederer (Dederer 1910) subjected cleaving embryos of echinoderms, molluscs and nemerteans to higher pressure and gravity, and concluded that in many cases the (altered) arrangement of blastomeres did not affect the developmental outcome in terms of cell fate.

These kinds of results were able to throw a wrench in the works of ‘mosaicist’ thinkers of the Roux school (who would have predicted that altered cleavage planes and blastomeres would result in changes in cell fate) and to spawn additional experiments to clarify the impact of cleavage on later patterning.

The Boveri group: cytology, formative substances and experimental embryology

Theodor Boveri and his collaborators followed chromosomes in mitosis and gametogenesis, using mainly nematode and echinoderm eggs/embryos. Their descriptions, which predated the founding of Roux’s Archive, laid the foundation for the concept that hereditary factors are associated with the nucleus and chromosomes. At the same time, researchers had to postulate that ‘formative substances’ contained within the cytoplasm of the egg and resulting blastomeres played an important role in modifying the hereditary factors, in order to impose different types of differentiation on different cells of the embryo. Part of the experimental work in Boveri’s group was therefore focused on identifying such formative substances in the egg.

Three papers from female students rotating through the Boveri lab during the first decade of the twentieth century dealt with topics of nuclei and formative substances in the oocyte. Alice Boring, actually enrolled at Bryn Mawr as one of T. Morgan’s students, visited the Boveri lab and published a paper in 1909 that investigated the dependence of nuclear size on temperature in the nematode Ascaris (Boring 1909). Previous studies had shown for various species that higher temperature results in smaller nuclear size; this, however, is not the case in Ascaris, which nicely supported Boring’s hypothesis that Ascaris eggs, which exist at very different temperatures at different stages of the natural life cycle, should be resistant to temperature changes. Two other papers attempt to learn more about formative substances in the egg. Mary J. Hogue centrifuged Ascaris eggs and thereby achieved a segregation of four layers, structurally defined by different types of granules (Hogue 1910). Hogue’s analysis of later stages allowed her to conclude that embryonic cell fate (e.g. animal vs vegetal cell) or spindle orientation, are not dependent on specific inclusions (i.e. these different granula per se do not represent ‘formative substances’); however, other conclusions from her work are difficult to extract clearly since a discussion or summary are missing. The professorial, or editorial oversight for this and many other papers published in the early 1900s leaves much to be desired!

A paper by Barbara Heffner (Heffner 1908) provides an outstanding historical and conceptual introduction into the quest for formative substances and the interpretation of their nature and function in echinoderm (sea urchin) embryos. The Boveri school of thought looked at these substances as discrete, localized yet dynamically interacting ‘molecules’, whereas Driesch emphasized a vague ‘polarity’ as the driving force behind regulation. Heffner cites Driesch’s characterization of regulation:

What is now being restored (= regulated; the authors): I never knew that and I don't know it now either. Also this required intimate structure (‘Intimstruktur’; = structural attribute of egg cytoplasm, the authors) can only mean a directedness, not more.

Heffner used a technique recently developed by Curt Herbst (see below) to expose early embryos to reduced calcium concentrations and thereby dissociate cells. Transient dissociation, followed by re-association, gave rise to larvae with skeletal pattern abnormalities. The author postulated that transient dissociation resulted in reshuffling of cell positions, and interpreted the resulting pattern defects in terms of localized formative substances inside the cells.

The Godlewski group: abiotic factors and development

The research program of Emil Godlewski, Professor of embryology at the University of Krakow, took its origin from the discoveries of Boveri and other cytologists. Godlewsky had described details of spermatogenesis and fertilization in various invertebrate taxa, subjecting gametes to different environmental conditions (‘abiotic factors’), and conducting cross-breeding experiments that, among other discoveries, supported the important role of the sperm cytoplasm during fertilization and early development (Fangerau and Müller 2007). Three papers in our collection of early woman-authored publications all appeared in 1913 attest to Godlewski’s interest in the role of abiotic factors in development. Janina Bury subjected sea urchin eggs and early cleavage stages to 0° temperature and analyzed its effect on chromosomes, nuclei and cleavage patterns (Bury 1913). She drew many conclusions, some of them with general importance for the field:

The size and shape of the chromosomes can be influenced by external factors. The size of the nuclear surface is directly proportional to the amount of chromatin contained in the nucleus at the time of chromosome formation, apart from the shape, size and number of chromosomes.

Janina Zielinska (Zielińska 1913) and Laura Kaufman (Kaufman 1913) were given different projects. The former investigated the effect of oxygen concentration on the regeneration process in annelids, and the latter conducted a detailed histological study of a peculiar phenomenon in amphibian development, the degeneration of part of the embryos in viviparous salamanders. Focusing on which embryo survives, and which dies, as well as the sequence of degenerative events in embryos about to die, Kaufman found that degeneration does not depend on yolk content, or on closeness to the uterus wall; she also concluded that parts of the embryos that degenerate first (e.g. anterior parts of the nervous system) are those that, in regeneration experiments performed with adults of the same species, are least capable of regeneration. At a later date, while working at the University of Krakow and the associated ‘State Institute for Agriculture’ in Pulawy (Poland), Kaufman authored a paper in DGE (Kaufman 1930) that investigated in great detail the effect of abiotic factors on growth in different bird species.

The Spemann group: induction, polarity, symmetry and the organizer

Hans Spemann began his career as a student of Boveri at the University of Würzburg (Germany), carrying out microscopic studies on the development of nematodes, one of the main ‘model organisms’ in the Boveri lab. Spemann’s research interest became focused on the ‘formative stimuli’ that must act during development of regulative systems to direct cell fate. Spemann used microsurgical experiment on embryos and pioneered the concepts of induction (Spemann 1901) and (morphogenetic) fields, culminating in the discovery of the organizer (Spemann and Mangold 1924) (Horder 2001). As a Professor in Berlin and later Freiburg, Spemann hosted a number of female graduate students, assistants and visiting scientists who worked on induction and the nature of the inducing agent.

Hedwig Wilhelmi was one of Spemann’s assistants in Berlin. She had done her PhD work on polarity and left–right symmetry in echinoderms, and followed this interest when working with Spemann in Berlin. Her first paper in DGE (Wilhelmi 1920) entails a thoughtful review of the literature on polarity and symmetry in different animal taxa, concluding that both of these attributes represent independently induced phenomena (‘abhängige Differenzierungen’). In a paper published in 1921, Wilhelmi analyzed the origin of left–right symmetry in amphibian embryos, using experimentally induced embryo duplications (twinning), as well as surgical ablation of small parts of the gastrula (Wilhelmi 1921). She came to the conclusion that

Situs inversus viscerum (reversal of normal left–right symmetry of inner organs; the authors) can be created experimentally by removal of a piece on the left side of the gastrula… (Situs inversus in twins)…is explained by the fact that the left half of the germ has something that the right half does not have… In the absence of this influence, it seems to be left to chance whether the intestine curves to the left or to the right.

These findings presage by 80 years our current understanding of how the left-sided activation of Lefty and Nodal by ciliary dynamics in the node determine left–right asymmetry of the vertebrate embryo.

Gudrun Ruud was a Norwegian developmental biologist who visited and collaborated with colleagues, like Hans Spemann and Ross Harrison. She spent time in the Spemann lab in 1916–1917 and worked on experiments that ‘prepared the way’ for the final Mangold/Spemann organizer theory. In a co-authored paper with Spemann (Ruud et al. 1922), she investigated the regulative potential of the dorsal vs ventral half of the gastrula, concluding that only the dorsal half was able to give rise to a complete larva; this experiment ‘pre-localized’ the organizing activity to the dorsal embryo. Many other experiments conducted while working with Spemann were published later at the University of Oslo (Ruud 1925).

Spemann viewed the organizer as a center from which a ‘differentiation flow’ (Differenzierungsströmung) emanated in an anterior direction. Together with a graduate student, Else Wessel, he conducted surgical experiments where he divided left and right halves of a gastrula and then reunited both, but (by ablating part of the material) in such a way that the median planes of the two fused halves converged or diverged at different angles (Wessel 1926). This manipulation resulted in partial duplications of anterior or posterior body domains which supported the idea of the postulated ‘differentiation streams’.

Following the description of the organizer in 1924 (Spemann and Mangold 1924), many labs, including that of Spemann himself, initiated the search for the material substance responsible for the induction and ‘differentiative flow’. PhD student Else Wehmeier published her results in 1934 (Wehmeier 1934); subjecting the organizer tissue, as well as other parts of the embryo which could substitute for the ‘normal organizer’ (i.e. the dorsal mesoderm), to different chemical and physical treatments—she concluded that solvents like alcohol, acetone or acetic acid, as well as high temperature, did not remove the inductive capability altogether, but led to induction of neural tissue only, rather than a complete new embryonic axes. A long journey remained ahead to the point where the signalling pathways underlying organizer activity were unravelled.

Finally, we mention the contribution of the Spemann PhD student Salome Glücksohn who published in DGE in 1931 (Glücksohn 1931). Employing the technique of embryonic chimerae, workers in the Spemann group combined transplants from different species of amphibians that could be distinguished at the cellular level (pigmentation, nuclear size etc.). In order to evaluate the results of such manipulations, a detailed knowledge of the normal development of these different species was of importance. Glücksohn was given (against her wishes, according to her biographer Papaioannou (2019)) the ‘menial task’ to carry out such developmental descriptions of salamander limbs. Ironically (according to Papaioannou), her meticulously completed work, as well as the ‘anti-genetic’ attitude of her mentor, later enabled and motivated her to carry out the characterization of developmental phenotypes in mouse mutant embryos (Gluecksohn-Schoenheimer 1938), and set her on a path as one of the pioneers who worked towards a synthesis between genetics and developmental mechanics.

The Herbst group: regeneration, heteromorphosis and pigmentation in salamanders

Curt Herbst started out as a student of Ernst Haeckel, carrying out comparative embryological studies on crustaceans (Oppenheimer 1970). Teaming up with Hans Driesch at the Zoological Station at Naples, Herbst turned to experimental studies on sea urchin embryos and other ‘regulative systems’. Specifically, he investigated the effect of salinity and other abiotic factors on development, and came across the pioneering observation that lowering the calcium concentration resulted in dissociation of blastomeres; this became an important research tool for many other workers (see above). In addition, motivated by the quest for ‘formative stimuli’ controlling developmental fate, he worked extensively on regeneration, as well as the development/physiology of skin pigmentation which (in amphibians) is under the ‘formative’ influence of the pituitary gland.

The works of two students of Herbst, Eva Keil and Eva Borchardt, attended to questions of regeneration. Eva Keil investigated regulative phenomena in regenerating flatworms (Keil 1924). She took advantage of an easily quantifiable natural marker, the fringe of eye spots that surrounds the anterior part of the body of the species Polycelis nigra, and correlated position and orientation of surgical cuts with the regenerating eye pattern. Eva Borchardt (1927) studied a different system, the heteromorphic regeneration of insect antennae (Borchardt 1927). In a number of earlier studies, Herbst himself had noted that removal of the eye in crustaceans resulted in the regeneration of an antenna at the place of an eye; he had also found that neural tissue emits a ‘formative stimulus’ important for the decision of whether the regenerating tissue develops into an eye or an antenna (Herbst 1916). In insects, removal of an antenna resulted in regrowth of a leg, depending on where the cut is made. Specifically, Borchardt noted that the maintained presence of the (neural) auditory organ at the base of the antenna was required to specify the regenerate as antenna; in the absence of the auditory organ, leg development ensued. Interestingly, the implications of these homeotic transformations for genetic determination of organ fate as we now understand it was not explicitly mentioned by Borchardt or her advisor.

Another PhD student of Herbst, Lore Marx, investigated the effect of the pituitary gland on skin pigmentation in salamanders (Marx 1929). Previous work in multiple labs had shown that larvae and young salamanders are able to adapt their pigmentation within hours to the colour of their environment (‘physiological color change’), and that contraction or extension of pigment cells (melanophores) were responsible for the colour change. It had also been elaborated that part of the pituitary (hypophysis) was instrumental in the physiological colour change; extirpation of the pituitary resulted in permanent contraction and later loss of melanophores. Marx’ experiments, ablating different parts of the pituitary at different time points, were able to shed more light on the nature of the physiological colour change. These and other results on environmentally induced colour changes in amphibians also drew Herbst into the debate around inheritance of acquired traits (see below).

The Przibram group: eco-evo-devo, pigmentation of insect pupae and inheritance of acquired traits

H. Przibram started out as a comparative embryologist who from early on joined the experimental program of W. Roux. He also fell under the influence of fin de siècle philosophical currents that emphasized the influence of the whole on the parts, and tried to initiate research that could treat this influence mathematically. Przibram founded (and financed!) a new experimental institute, the ‘Wiener Biologische Versuchsanstalt’ (Vienna Institute for Experimental Biology, Austria), where he attracted collaborations with many international researchers. The institute is considered by some contemporary historians as a precursor of modern ‘eco-evo-devo’ (Drack et al. 2007). That being said, a number of controversial studies came out of the ‘Versuchsanstalt’, possibly brought about by its founder’s following of non-mainstream scientific theories, such as the inheritance of acquired traits. In a paper published right after opening the Versuchsanstalt (Przibram 1912) he writes:

The question of the inheritance of acquired characters has entered a new stage. It is no longer a question of whether characters that became visible on the body of the parents..are expressed by the progeny. This question, due to experiments on almost all major groups of the animals and plants, has been answered in the affirmative. Rather, the only question now is how the changes in the progeny are brought about.

A long series of papers was published in DGE by a female student, and later collaborator/assistant of Przibram, Leonore Brecher. All of these extraordinarily detailed and quantitative studies focused on the influence of the environment on the pigmentation of butterfly pupae. We surmise that the initial trigger for this topic came from Brecher’s PhD adviser’s interest in the connection between environment-development-inheritance, and a recent review (Nahm 2021) even cites a publication by her in which she comments on the inheritability of experimentally induced pupal colorations in the next generation (Fig. 7).

Fig. 7

The pupae of Pieris brassicae L. show colour adaptation on different backgrounds. Image from Brecher (Brecher 1917)

However, none of the eight papers published in DGE between 1917 and 1925 contains any mention of the inheritability of environmentally induced pupal color patterns. Only in the paper co-authored with her advisor (Przibram and Brecher 1919) is an explicit connection made between the ‘coat colour’ of animals (in general) and the possibility of inheritance of acquired traits. We may deal here, in Brecher’s other writing, with an admirable case of focusing on the facts, rather than being carried away by far-reaching yet unsubstantiated speculations that must have surrounded her in the presence of her advisor and her collaborators.

Brecher’s 1917 paper is divided into three parts that report the findings of her PhD thesis on Pieris brassicae (Brecher 1917). Later papers (among others, (Brecher 1919, 1922, 1924)) extend her research to other species, and also address different questions. Pupae of certain species of butterfly are able to adopt different colorations, depending on the colour/pattern of the leaves the preceding larvae were raised on. Brecher’s research investigates the types of colour pigments responsible for the pupal coloration; she determines that it is the colour wavelength (rather than intensity) that is responsible for pupal coloration; and she showed that environmental colour information reaches the pupa via the larval eye. This discovery, based on simple but effective manipulations (extirpation of larval eyes; covering larval eyes with differentially coloured varnishes), discredited previous reports that the pupal colour pattern did not depend on larval colour input, and formed the basis for numerous subsequent studies.

The Gurwitsch group: morphogenetic fields and mitogenic radiation

Alexander Gurwitsch studied and later practiced histology around the turn of the twentieth century. He also became fascinated with developmental questions. Experimental studies, like transplantation-induction experiments initiated by H. Spemann (see above) led to the concept of a ‘morphogenetic field’, as a developmental unit where cells in some manner ‘communicate’ with each other, or are influenced in their behavior by common internal or external factors that ‘tune’ the behavior of cells within the field. Gurwitsch focused his interest on the ‘force’ acting over certain distances within a field, and originated the concept of ‘mitogenic radiation’, weak light emission in the UV range caused by living material, like dividing cells, and influencing other cells at a distance. This concept sparked great interest (and number of publications) from the 1920s to the 1940s, but then virtually disappeared following many studies that were unable to replicate Gurwitsch’s findings (e.g. Barth and Glasser 1939; Glasser 1940; Stern 1975). Some interest in mitogenic radiation reappeared (in fields other than developmental biology) in recent decades (Volodyaev and Beloussov 2015). We do not want to go into any detail of the historical and ongoing debate about the reality of mitogenic radiation, but merely point at the significant number of woman-authored DGE papers by the Gurwitschs (both his wife Lydia and daughter Nina formed an integral part of his research group) as well as female students working with them in 1920s. The papers by A. Gurwitsch and N. Gurwitsch (Gurwitsch and Gurwitsch 1924) and L. Gurwitsch (Gurwitsch 1924) are the first substantial publications on mitogenic radiation; they describe the experimental setup, consisting of the juxtaposition of two mitotically active tissues (e.g. onion roots, bacterial or yeast cultures), whereby one acts as an inducer (of mitosis), the other one as an induced tissue in which the effect on mitotic rate is statistically evaluated. Later papers (Kisliak-Statkewitsch 1927; Sussmanowitsch 1928) investigated other details concerning the effect of this radiation in other plant species, and reported on phenomena like ‘exhaustion’ of an induced tissue to react positively to the inducing agent after a given time interval.

Genetics: from American flies via Lenin’s brain to Berlin flies

Coming closer to the end of our investigation on research topics followed by women researchers who published in DGE during the first decades of its existence, we need to look back to T.H. Morgan and his group. Morgan is of course best known as the ‘father of classical genetics’, and much has been written about the ‘rebirth’ of this field around the turn of the twentieth century. Pivotal was the rediscovery of Mendel’s laws of genetic recombination by several scientists, as well as the insight that chromosomes carry the genetic information transmitted from one generation to the next (Sutton-Boveri chromosome theory; (Wilson 1925)). In this context (as already briefly mentioned above), the microscopic analysis of developing gametes played an outstanding role. A number of microscopists had noted the presence of a special chromosome in the developing sperm of various insect taxa (see, for a nice time line of seminal discoveries Carey et al. 2022). Morgan’s collaborator Nettie Stevens, as an avid microscopist, also worked on this topic, in parallel to her studies on regeneration referenced above. In 1905 and the following years, Stevens published a number of pioneering papers (not in DGE) that identified the Y chromosome in males of several insect taxa, including Drosophila (cited in Carey et al. 2022). It stands to reason that the reorientation of Morgan’s work towards genetics, and the use of Drosophila as the first ‘genetic model system’ was strongly influenced by Stevens’ work. Morgan’s first seminal paper in the field of genetics showed the linkage of the white gene to the female sex chromosome. This and virtually all other pioneering papers in genetics were not published in DGE, perhaps reflecting the growing rift between developmental mechanics and genetics.

Drosophila genetics spread from Morgan’s ‘fly room’ at Columbia University towards other laboratories, notably in Russia, where fly labs were founded in Leningrad (Y. Filipchenko) and Moscow (N. K. Koltsov and S. S. Chetverikov) right after the October revolution. Filipchenko and Chetverikov mentored several geneticists, among them Theodosius Dobzhansky (who later joined T. Morgan’s group at CalTech) and the couple Elena and Nicolai Timofeeff-Ressovsky (Kulikov 2022). The Timofeeff-Ressovskys formed part of a science-historically unique collaboration between the genetics institute in Moscow and the German ‘Kaiser Wilhelm-Institute for Brain Research’ in Berlin. The director of this institute, Oscar Vogt was a renowned neuroanatomist, but also had a strong interest in genetics and evolution. He formed a collaboration with the genetics institute in Moscow; he himself was offered the unique task to investigate neuroanatomical features of the brain of Lenin, who had just died; at the same time, working in Moscow, he attracted the Timofeeff-Ressovskys to his institute in Berlin, where they worked until 1945 (Laubichler and Sarkar 2002). The three publications contributed to DGE by the Timofeeff-Ressovskys between 1926 and 1928 are pioneering papers in classical genetics, even though, due to the fact that they were written in German, and even more so due to political and ideological bias against Germany and Russia, they did not find immediate acceptance in the anglophone literature. The first paper ‘On the phenotypic manifestation of the Genotype. II. On idio-somatic variation groups in Drosophila funebris’ (Timoféeff-Ressovsky and Timoféeff-Ressovsky 1926) focused on the fundamental concept of how a gene controls a certain phenotype. According to this paper, a gene ‘a’, together with other genes (‘b’, ‘c’,…), modulates a certain factor ‘a’; this factor ‘a’ then can be further influenced by environmental factors (‘m’, ‘n’, ‘o’, ‘p’…) to ultimately determine phenotypic attribute ‘A’. This means that what is genetically controlled is no