On the origin of the typological/population distinction in Ernst Mayr’s changing views of species, 1942–1959

Ernst Mayr’s typological/population distinction is a conceptual thread that runs throughout much of his work in systematics, evolutionary biology, and the history and philosophy of biology. Mayr himself claims that typological thinking originated in the philosophy of Plato and that population thinking was first introduced by Charles Darwin and field naturalists. A more proximate origin of the typological/population thinking, however, is found in Mayr’s own work on species. This paper traces the antecedents of the typological/population distinction by detailing Mayr’s changing views of species between 1942 and 1955. During this period, Mayr struggles to refine the biological species concept in the face of tensions that exist between studying species locally and studying them as geographically distributed collections of variable populations. The typological/population distinction is first formulated in 1955, when Mayr generalizes from the type concept versus the population concept in taxonomy to typological versus population thinking in biology more generally. Mayr’s appeal to the more general distinction between typological and population thinking coincides with the waning status of natural history and evolutionary biology that occurs in the early 1950s and the distinction plays an important role in Mayr’s efforts to legitimate the natural historical sciences.     

Causal mechanisms of evolution and the capacity for niche construction

Ernst Mayr proposed a distinction between “proximate”, mechanistic, and “ultimate”, evolutionary, causes of biological phenomena. This dichotomy has influenced the thinking of many biologists, but it is increasingly perceived as impeding modern studies of evolutionary processes, including study of “niche construction” in which organisms alter their environments in ways supportive of their evolutionary success. Some still find value for this dichotomy in its separation of answers to “how?” versus “why?”questions about evolution. But “why is A?” questions about evolution necessarily take the form “how does A occur?”, so this separation is illusory. Moreover, the dichotomy distorts our view of evolutionary causality, in that, contra Mayr, the action of natural selection, driven by genotype-phenotype-environment interactions which constitute adaptations, is no less “proximate” than the biological mechanisms which are altered by naturally selected genetic variants. Mayr’s dichotomy thus needs replacement by more realistic, mechanistic views of evolution. From a mechanistic viewpoint, there is a continuum of adaptations from those evolving as responses to unchanging environmental pressures to those evolving as the capacity for niche construction, and intermediate stages of this can be identified. Some biologists postulate an association of “phenotypic plasticity” (phenotype-environment covariation with genotype held constant) with capacity for niche construction. Both “plasticity” and niche construction comprise wide ranges of adaptive mechanisms, often fully heritable and resulting from case-specific evolution. Association of “plasticity” with niche construction is most likely to arise in systems wherein capacity for complex learning and behavioral flexibility have already evolved.     

Proximate and ultimate causes: how come? and what for?

Proximate and ultimate causes in evolutionary biology have come to conflate two distinctions. The first is a distinction between immediate and historical causes. The second is between explanations of mechanism and adaptive function. Mayr emphasized the first distinction but many evolutionary biologists use proximate and ultimate causes to refer to the second. I recommend that ‘ultimate cause’ be abandoned as ambiguous.     

More on how and why: cause and effect in biology revisited

In 1961, Ernst Mayr published a highly influential article on the nature of causation in biology, in which he distinguished between proximate and ultimate causes. Mayr argued that proximate causes (e.g. physiological factors) and ultimate causes (e.g. natural selection) addressed distinct ‘how’ and ‘why’ questions and were not competing alternatives. That distinction retains explanatory value today. However, the adoption of Mayr’s heuristic led to the widespread belief that ontogenetic processes are irrelevant to evolutionary questions, a belief that has (1) hindered progress within evolutionary biology, (2) forged divisions between evolutionary biology and adjacent disciplines and (3) obstructed several contemporary debates in biology. Here we expand on our earlier (Laland et al. in Science 334:1512–1516, 2011) argument that Mayr’s dichotomous formulation has now run its useful course, and that evolutionary biology would be better served by a concept of reciprocal causation, in which causation is perceived to cycle through biological systems recursively. We further suggest that a newer evolutionary synthesis is unlikely to emerge without this change in thinking about causation.     

Ronald Brady and the cladists

Ronald Brady was the first philosopher to defend pattern cladistics as an independent scientific field. That independence was achieved through the decoupling of biological systematics from phylogenetics––that is, inferred evolutionary processes (e.g. character transformation). Brady saw parallels between biological systematics and Wolfgang von Goethe's Morphology, an empirical scientific field that incorporates human observation and perception to discover coherent morphological structures. Goethe's Morphology and pre-Darwinian systematics were independent from evolutionary narratives, a tradition that continued into the 20th Century through the work of biologists such as Agnes Arber. Most importantly, Brady provided the philosophical and historical foundations to an independent systematics by demonstrating the links between phenomenology, Goethe's Morphology and comparative biology.     

Ernst Mayr's 'ultimate/proximate' distinction reconsidered and reconstructed

It's been 41 years since the publication of Ernst Mayr's Cause and Effect in Biology wherein Mayr most clearly develops his version of the influential distinction between ultimate and proximate causes in biology. In critically assessing Mayr's essay I uncover false statements and red-herrings about biological explanation. Nevertheless, I argue to uphold an analogue of the ultimate/proximate distinction as it refers to two different kinds of explanations, one dynamical the other statistical.     

Ultimate explanations concern the adaptive rationale for organism design

My understanding is that proximate explanations concern adaptive mechanism and that ultimate explanations concern adaptive rationale. Viewed in this light, the two kinds of explanation are quite distinct, but they interact in a complementary way to give a full understanding of biological adaptations. In contrast, Laland et al. (2013)—following a literal reading of Mayr (Science 134:1501–1506, 1961)—have characterized ultimate explanations as concerning any and all mechanisms that have operated over the course of an organism’s evolutionary history. This has unfortunate consequences, such as allowing random drift to form the basis for ultimate explanations, and allowing proximate and ultimate explanations to bleed into each other until their distinction is meaningless. Here, I suggest Laland et al’s explanatory framework of “reciprocal causation” is not conducive to successful biological science, and that they have misunderstood key elements of the theory of Darwinian adaptation.     

Styles of scientific reasoning: Adolf Remane (1898–1976) and the German evolutionary synthesis

Adolf Remane is widely considered to have been one of the most influential German zoologists of the 20th Century, yet Ernst Mayr persistently characterized him as an idealistic morphologist, that is, a typologist unable to understand population genetics or indeed Darwinian theory. This stands in sharp contrast to Mayr's praise for Bernhard Rensch as one of the most important German contributors to the Modern Synthesis of evolutionary theory. Remane's style of scientific reasoning is analysed in his writings on microsystematics, ecology, comparative morphology and phylogenetics and found to be highly consistent throughout these varied fields of research, while differing fundamentally from the eminently statistical foundations of both population genetics and natural selection theory that were embraced by Mayr. A comparative analysis of Rensch's understanding of science in general, and biology in particular, shows him to share core values with Remane, both authors rooted in the Mandarin tradition of the German professoriate. Biographical and socio‐political factors appear to have influenced Mayr's contrasting perception of Remane and Rensch, one that would influence later biologists and historians of science.     

Dual Causality and the Autonomy of Biology

Ernst Mayr’s concept of dual causality in biology with the two forms of causes (proximate and ultimate) continues to provide an essential foundation for the philosophy of biology. They are equivalent to functional (=proximate) and evolutionary (=ultimate) causes with both required for full biological explanations. The natural sciences can be classified into nomological, historical nomological and historical dual causality, the last including only biology. Because evolutionary causality is unique to biology and must be included for all complete biological explanations, biology is autonomous from the physical sciences.     

Mayr's view of Darwin: was Darwin wrong about speciation?

We commonly read or hear that Charles Darwin successfully convinced the world about evolution and natural selection, but did not answer the question posed by his most famous book, ‘On the Origin of Species …’. Since the 1940s, Ernst Mayr has been one of the people who argued for this point of view, claiming that Darwin was not able to answer the question of speciation because he failed to define species properly. Mayr undoubtedly had an important and largely positive influence on the study of evolution by stimulating much evolutionary work, and also by promoting a ‘polytypic species concept’ in which multiple, geographically separated forms may be considered as subspecies within a larger species entity. However, Mayr became seduced by the symmetry of a pair of interlocking ideas: (1) that coexistence of divergent populations was not possible without reproductive isolation and (2) reproductive isolation could not evolve in populations that coexist. These beliefs led Mayr in 1942 to reject evidence of the importance of intermediate stages in speciation, particularly introgression between hybridizing species, which demonstrates that complete reproductive isolation is not necessary, and the existence of ecological races, which shows that ecological divergence can be maintained below the level of species, in the face of gene flow. Mayr's train of thought led him to the view that Darwin misunderstood species, and that species were fundamentally different from subspecific varieties in nature. Julian Huxley, reviewing similar data at the same time, came to the opposite conclusion, and argued that these were the intermediate stages of speciation expected under Darwinism. Mayr's arguments were, however, more convincing than Huxley's, and this caused a delay in the acceptance of a more balanced view of speciation for many decades. It is only now, with new molecular evidence, that we are beginning to appreciate more fully the expected Darwinian intermediates between coexisting species. © The Author. Journal compilation © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 3–16.     

Ernst Mayr,naturalist: His contributions to systematics and evolution

Ernst Mayr's scientific career continues strongly 70 years after he published his first scientific paper in 1923. He is primarily a naturalist and ornithologist which has influenced his basic approach in science and later in philosophy and history of science. Mayr studied at the Natural History Museum in Berlin with Professor E. Stresemann, a leader in the most progressive school of avian systematics of the time. The contracts gained through Stresemann were central to Mayr's participation in a three year expedition to New Guinea and The Solomons, and the offer of a position in the Department of Ornithology, American Museum of Natural History, beginning in 1931. At the AMNH, Mayr was able to blend the best of the academic traditions of Europe with those of North America in developing a unified research program in biodiversity embracing systematics, biogeography and nomenclature. His tasks at the AMNH were to curate and study the huge collections amassed by the Whitney South Sea Expedition plus the just purchased Rothschild collection of birds. These studies provided Mayr with the empirical foundation essential for his 1942Systematics and the Origin of Species and his subsequent theoretical work in evolutionary biology as well as all his later work in the philosophy and history of science. Without a detailed understanding of Mayr's empirical systematic and biogeographic work, one cannot possibly comprehend fully his immense contributions to evolutionary biology and his later analyses in the philosophy and history of science.     

Species: Beasts of burden

Ernst Mayr (1904–2005) was the twentieth century's most influential writer to wrestle with the species problem. 1 - 4 The following draws heavily on his work, albeit without presumptuously claiming to mirror his thinking or present any original ideas. As a personal meditation, I am thinking mostly of platyrrhines. Following Mayr, I adhere to what is commonly called the Biological Species Concept (BSC) as a way of thinking about a species in the real‐world biosphere as a taxon. I also hold to the idea that the Linnaean category called species has the same function as other categories: a linguistic tool for organizing and retrieving information about biodiversity while embodying evolutionary hypotheses. In other words, alpha taxonomy, the area of systematics that involves identifying, naming, and classifying species, is not purely an exercise in either biology or inventory because it involves communication as well. The burdensome work of the species category stems partly from tension created by the several purposes associated with the concept: the objective observation and examination of a fundamental biological phenomenon, the collection and interpretation of data in a selective context of relevance, and the intention to deploy scientific decisions as a form of communication within a dynamic but highly structured language system.     

The Philosophy of Donald T. Campbell: A Short Review and Critical Appraisal

Aside from his remarkable studies in psychology and the social sciences, Donald Thomas Campbell (1916–1996) made significant contributions to philosophy, particularly philosophy of science,epistemology, and ethics. His name and his work are inseparably linked with the evolutionary approach to explaining human knowledge (evolutionary epistemology). He was an indefatigable supporter of the naturalistic turn in philosophy and has strongly influenced the discussion of moral issues (evolutionary ethics). The aim of this paper is to briefly characterize Campbells work and to discuss its philosophical implications. In particular, I show its relevance to some current debates in the intersection of biology and philosophy. In fact, philosophy of biology would look poorer without Campbells influence. The present paper is not a hagiography but an attempt to evaluate and critically discuss the meaning of Campbells work for philosophy of biology and to encourage scholars working in this field to read and re-read this work which is both challenging and inspiring.     

Georges Teissier (1900–1972) and the Modern Synthesis in France

This Perspectives is devoted to the ideas of the French zoologist Georges Teissier about the mechanisms of evolution and the relations between micro- and macroevolution. Working in an almost universally neo-Lamarckian context in France, Teissier was one of the very few Darwinians there at the time of the evolutionary synthesis. The general atmosphere of French zoology during the 1920s and the 1930s will first be recalled, to understand the specific conditions in which Teissier became a zoologist. After a brief overview of his joint work with Philippe L’Héritier on the experimental genetics of Drosophila, this article describes the ways Teissier, during the 1950s, conceptualized the mechanisms that could allow for macroevolutionary transitions.IT is usually acknowledged that France did not significantly participate in the elaboration of 20th century evolutionary theory, often designated The Modern Synthesis. In their classical book on the history of the synthesis, Ernst Mayr and William B. Provine devoted a whole—nonetheless small—chapter to this specific issue (Mayr and Provine 1998, pp. 309–328). Mayr clearly stated that “France is the only major scientific nation that did not contribute significantly to the evolutionary synthesis” (Mayr 1998, p. 309). In the absence of a French architect of the synthesis, Mayr and Provine asked Ernest Boesiger, a Swiss population geneticist and a former student of Georges Teissier, to tell the story of what had happened in French biology at the time of the evolutionary synthesis. Boesiger, who died in 1975, wrote a paper in 1974 that provided the firm basis of the chapter. In very strong terms, he depicted French biology as “a kind of living fossil in the rejection of modern evolutionary theories” (Boesiger 1998, p. 309). He insisted on the fact that, even in 1974, most French biologists and philosophers were still reluctant to accept Darwinism. As regards the period of the 1930s, Boesiger was able to think of only two exceptions: Georges Teissier and Philippe L’Héritier. He then referred to their joint research in population genetics, which was based on the new technique of the population cages with the species Drosophila melanogaster, and listed their contributions to this new discipline.If Teissier and L’Héritier’s works on Drosophila are nowadays more widely recognized than in 1974, due in particular to the efforts of Jean Gayon and Michel Veuille (Gayon and Veuille 2001), this recognition could have as an unintended consequence the reduction of both Teissier and L’Héritier to being simply the inventors of a useful technique, namely the population cages (see especially how Mayr presented their work in his other classical book, Mayr 1982, p. 574), or as the founders of a French school of population geneticists (Gayon and Veuille 2001). The aim of this article is to reevaluate the way Georges Teissier (1900–1972) conceived Darwinian natural selection not only as an important mechanism for evolution at the population level but more fundamentally as a general key for the unification of biology, exactly as Julian Huxley or Ernst Mayr did during the same period (1930–1970). However, starting in the early 1950s, Teissier went on to conceive a very specific understanding of the evolutionary synthesis.In this article, I will first describe the general atmosphere of evolutionary issues in French biology at the time when Teissier started working as a zoologist, to understand against what he developed his joint research program with L’Héritier and afterward his general conceptions about evolution. During the 1930s and the 1940s, only a very few scientists in France could be seen as Darwinians. In addition to Teissier and L’Héritier, one may also consider Marcel Prenant, Boris Ephrussi, and the mathematician Gustave Malécot. Building on Jean Gayon and Michel Veuille’s work, I will then give a quick overview of L’Héritier and Teissier’s most important achievements in the field of population genetics. In the third part, I will discuss the discovery made by Teissier and L’Héritier of a case of cytoplasmic inheritance in Drosophila. This unexpected finding led them into the field of non-Mendelian heredity. I will then develop in detail the way Teissier finally went on to conceive the relation between microevolution and macroevolution, in light of the general context of French biology and of the development of the field of cytoplasmic inheritance.     

The individuality of the species: A Darwinian theory? — from Buffon to Ghiselin, and back to Darwin

Since the 1970s, there has been a tremendous amount of literature on Ghiselin's proposal that “species are individuals”. After recalling the origins and stakes of this thesis in contemporary evolutionary theory, I show that it can also be found in the writings of the French naturalist Buffon in the 18th Century. Although Buffon did not have the conception that one species could be derived from another, there is an interesting similarity between the modern argument and that of Buffon regarding the “individuality of species’. The analogy is strong enough to force us to recognize that genuine evolutionary (or Darwinian) questions might be of secondary importance in the discussion. In consequence, the third section of the paper proposes an alternative schema for the “logical structure” of the Darwinian concept of species. Darwin distinguished the problem of the designation of a concrete species, and the problem of its signification of species within his theory of descent? The resulting notion of species involves a logical structure based on the fusion of the logical operations of classification and ordering. The difficulty — and interest — is that this interpretation of species does not entail any precise operational definition of species; it can only tell us what the ultimate signification of classification is within the theory of descent with modification through natural selection.     

In defense of Louis Pasteur: Critique of Gerald Geison's deconstruction of Pasteur's discovery of molecular chirality

Louis Pasteur discovered the phenomenon of molecular chirality, based on his studies of tartrate crystals. His finding remains one of the most important discoveries in the history of chemistry and a fundamentally important chemical phenomenon, with essential implications in biology. In his 1995 book The Private Science of Louis Pasteur, the eminent historian of science Gerald L. Geison (1943‐2001) was highly critical of much of Pasteur's work including his discovery of molecular chirality. The in‐depth analysis provided in this article indicates, however, that the negative assessment of Pasteur's chirality work by Geison is entirely without scientific basis. Criticisms of Pasteur in the book for other “transgressions” in his chirality work, such as supposed influences of his personal biases and stubbornly held a priori notions, misrepresentation of his scientific work in his publications and lectures, and unethical and career‐minded conduct, are also not supported by the evidence. Other troubling features of the book include a broad failure to assure accuracy in a variety of fundamental and important information, including errors in names, dates, events, referencing, indexing, and French‐language text.     

Reflections on Systematics and Phylogenetic Reconstruction

I attempt to raise questions regarding elements of systematics—primarily in the realm of phylogenetic reconstruction—in order to provoke discussion on the current state of affairs in this discipline, and also evolutionary biology in general: e.g., conceptions of homology and homoplasy, hypothesis testing, the nature of and objections to Hennigian “phylogenetic systematics”, and the schism between (neo)Darwinian descendants of the “modern evolutionary synthesis” and their supposed antagonists, cladists and punctuationalists.     

Pattern Cladistics and the ‘Realism–Antirealism Debate’ in the Philosophy of Biology

Despite the amount of work that has been produced on the subject over the years, the ‘transformation of cladistics’ is still a misunderstood episode in the history of comparative biology. Here, I analyze two outstanding, highly contrasting historiographic accounts on the matter, under the perspective of an influential dichotomy in the philosophy of science: the opposition between Scientific Realism and Empiricism. Placing special emphasis on the notion of ‘causal grounding’ of morphological characters (sensu Olivier Rieppel) in modern developmental biology’s (mechanistic) theories, I arrive at the conclusion that a ‘new transformation of cladistics’ is philosophically plausible. This ‘reformed’ understanding of ‘pattern cladistics’ entails retaining the interpretation of cladograms as ‘schemes of synapomorphies’, but in association to construing cladogram nodes as ‘developmental-genetic taxic homologies’, instead of ‘standard Darwinian ancestors’. The reinterpretation of pattern cladistics presented here additionally proposes to take Bas Van Fraassen’s ‘constructive empiricism’ as a philosophical stance that could properly support such analysis of developmental-genetic data for systematic purposes. The latter suggestion is justified through a reappraisal of previous ideas developed by prominent pattern cladists (mainly, Colin Patterson), which concerned a scientifically efficient ‘observable/non-observable distinction’ linked to the conceptual pair ‘ontogeny and phylogeny’. Finally, I argue that a robust articulation of Antirealist alternatives in systematics may provide a rational basis for its disciplinary separation from evolutionary biology, as well as for a critical reconsideration of the proper role of certain Scientific Realist positions, currently popular in comparative biology.     

On Reciprocal Causation in the Evolutionary Process

Recent calls for a revision of standard evolutionary theory (SET) are based partly on arguments about the reciprocal causation. Reciprocal causation means that cause–effect relationships are bi-directional, as a cause could later become an effect and vice versa. Such dynamic cause-effect relationships raise questions about the distinction between proximate and ultimate causes, as originally formulated by Ernst Mayr. They have also motivated some biologists and philosophers to argue for an Extended Evolutionary Synthesis (EES). The EES will supposedly expand the scope of the Modern Synthesis (MS) and SET, which has been characterized as gene-centred, relying primarily on natural selection and largely neglecting reciprocal causation. Here, I critically examine these claims, with a special focus on the last conjecture. I conclude that reciprocal causation has long been recognized as important by naturalists, ecologists and evolutionary biologists working in the in the MS tradition, although it it could be explored even further. Numerous empirical examples of reciprocal causation in the form of positive and negative feedback are now well known from both natural and laboratory systems. Reciprocal causation have also been explicitly incorporated in mathematical models of coevolutionary arms races, frequency-dependent selection, eco-evolutionary dynamics and sexual selection. Such dynamic feedback were already recognized by Richard Levins and Richard Lewontin in their bok The Dialectical Biologist. Reciprocal causation and dynamic feedback might also be one of the few contributions of dialectical thinking and Marxist philosophy in evolutionary theory. I discuss some promising empirical and analytical tools to study reciprocal causation and the implications for the EES. Finally, I briefly discuss how quantitative genetics can be adapated to studies of reciprocal causation, constructive inheritance and phenotypic plasticity and suggest that the flexibility of this approach might have been underestimated by critics of contemporary evolutionary biology.