Populations

The impressive variation amongst biological individuals generates many complexities in addressing the simple-sounding question what is a biological individual? A distinction between evolutionary and physiological individuals is useful in thinking about biological individuals, as is attention to the kinds of groups, such as superorganisms and species, that have sometimes been thought of as biological individuals. More fully understanding the conceptual space that biological individuals occupy also involves considering a range of other concepts, such as life, reproduction, and agency. There has (...) been a focus in some recent discussions by both philosophers and biologists on how evolutionary individuals are created and regulated, as well as continuing work on the evolution of individuality. (shrink)

Biologists, historians of biology, and philosophers of biology often ask what is it to be an individual, really. This book does not answer that question. Instead, it answers a much more interesting one: How do biologists individuate individuals? In answering that question, the authors explore why biologists individuate individuals, in what ways, and for what purposes. The cross-disciplinary, dialogical approach to answering metaphysical questions that is pursued in the volume may seem strange to metaphysicians who are not biologically focused, but (...) it is adroitly achieved by the editors. Scott Lidgard (a paleontologist and marine ecologist) and Lynn K. Nyhart (a historian of biology) orchestrate a dialogue among historians of biology, philosophers of biology, and practicing biologists over 10 chapters. These are followed by three reflective commentaries written to frame the different disciplinary perspectives and to highlight the historical, biological, and philosophical themes across the chapters. The result is a volume—in structure and in content—that has much to be generously commended. Biological individuality is a hotly discussed topic, but it is also part of a series of long-standing arguments within both the history and philosophy of biology (HPB) and metaphysics. Notable and fervent debates have centered on evolution and the units of selection, predominantly on Michael T. Ghiselin’s and David L. Hull’s notion of species as individuals, Peter Godfrey-Smith’s Darwinian individuals, and Ellen Clarke’s individuating mechanisms. Lately, it has encompassed non-Darwinian individuals, symbiotic associations like Thomas Pradeu’s immunological individuals, and John Dupré and Maureen A. O’Malley’s metabolic individuals.2 The present volume is curated in a way to introduce the reader to new research in HPB that articulates these debates as well as to introduce and engage in the study of further notions of biological individuality. But its aim is more than an introduction. As the subtitle suggests, it is also intended to give the reader insight into the working together of biologists, historians of biology, and philosophers of biology in figuring out how the notion of biological individuality is instantiated. As such, the problem-centered dialogue that results does more than talk through biological individuality. It shows how the different and often divergent goals of the authors’ disciplines shape not only how they think about individuality but how they communicate this thinking in reciprocal collaboration with others in different disciplines. … cont’d…. (shrink)

Contemporary biology has inherited two key assumptions from the Modern Synthesis about the nature of population lineages: sexual reproduction is the exemplar for how individuals in population lineages inherit traits from their parents, and random mating is the exemplar for reproductive interaction. While these assumptions have been extremely fruitful for a number of fields, such as population genetics and phylogenetics, they are increasingly unviable for studying the full diversity and evolution of life. I introduce the “mixture” account of population lineages (...) that escapes these assumptions by dissolving the Modern Synthesis’s sharp line separating reproduction and development and characterizing reproductive integration in population lineages by the ephemerality of isolated subgroups rather than random mating. The mixture account provides a single criterion for reproductive integration that accommodates both sexual and asexual reproduction, unifying their treatment under Kevin de Queiroz’s generalized lineage concept of species. The account also provides a new basis for empirically assessing the effect of random mating as an idealization on the empirical adequacy of population genetic models. (shrink)

With the further growth of the world population and the further intensification of the processes of interaction between countries and increasing movements of the masses of people, the role of Political Demography becomes more and more important. Issues of global ageing, migration, low fertility in developed countries (or very high fertility in some African countries), high mortality in many developing states (including deaths from AIDS); rapid change in the ethnic composition in Europe and in several other regions and many other (...) pressing issues are in the focus of this discipline. Some of these problems are analyzed in this yearbook. However, among those issues, the issue of global ageing becomes more and more pressing every year. It is sufficient to take into account the point that within two forthcoming decades a rapid global increase in the number of retirement-age persons will lead to its doubling within this fairly small historical period. The concerns about population ageing apply to both developed and many developing countries and it has turned into a global issue. In the next decades the population ageing is likely to become one of the most important processes determining the future society characteristics and directions of technological development. (shrink)

Процесс старения населения захватил не только развитые страны, но и многие развивающиеся, превратившись в глобальный. Представляется, что он будет одним из самых важных процессов в ближайшие десятилетия, определяющим облик общества буду-щего и направление развития технологий. В статье дается анализ некоторых параметров процесса старения населения, показыва-ются его важные следствия для общества и мира в целом. На ос-новании этого анализа делается вывод о том, что грядущий тех-нологический переворот (обозначаемый авторами как завершаю-щая фаза кибернетической революции) и предполагаемый шестой технологический уклад, связанный с наступающей (...) шестой конд-ратьевской волной, будут связаны в первую очередь с прорывами в медицине и смежных с ней технологиях. Также авторы представ-ляют свой взгляд на финансовые инструменты решения проблемы пенсионного обеспечения увеличивающегося пожилого населения в развитых странах. Они считают, что при более целенаправленном использовании денег пенсионных фондов, направлении их (при нуж-ных гарантиях) на образование и рост квалификации молодежи развивающихся стран возможно частично облегчить указанную проблему в развитых государствах. (shrink)

In the first part of this article we survey general similarities and differences between biological and social macroevolution. In the second (and main) part, we consider a concrete mathematical model capable of describing important features of both biological and social macroevolution. In mathematical models of historical macrodynamics, a hyperbolic pattern of world population growth arises from non-linear, second-order positive feedback between demographic growth and technological development. Based on diverse paleontological data and an analogy with macrosociological models, we suggest that the (...) hyperbolic character of biodiversity growth can be similarly accounted for by non-linear, second-order positive feedback between diversity growth and the complexity of community structure. We discuss how such positive feedback mechanisms can be modelled mathematically. (shrink)

The dichotomy between ‘typological thinking’ and ‘population thinking’ features in a range of debates in contemporary and historical biology. The origins of this dichotomy are often traced to Ernst Mayr, who is said to have coined it in the 1950s as a rhetorical device that could be used to shield the Modern Synthesis from attacks by the opponents of population biology. In this two-part essay I argue that the origins of the typology/population dichotomy are considerably more complicated and more interesting (...) than is commonly thought. In this first part, I will argue that Mayr's dichotomy was based on two distinct type/population contrasts that had been articulated much earlier by George Gaylord Simpson and Theodosius Dobzhansky. Their distinctions made eminent sense in their own, isolated contexts. In the second part, I will show how Mayr conflated these type/population distinctions and blended in some of his own, unrelated concerns with ‘types’ of a rather different sort. Although Mayr told his early critics that he was merely making “a temporary oversimplification,” he ended up burdening the history and philosophy of biology with a troubled dichotomy. (shrink)

We argue for a new conventionalism about many kinds of evolutionary groups, including clades, cohesive units, and populations. This rejects a consensus, which says that given any one of the many legitimate grouping concepts, only objective biological facts determine whether a collection is such a group. Surprisingly, being any one kind of evolutionary group typically depends on which of many incompatible values are taken by suppressed variables. This is a novel pluralism underlying most any one group concept, rather than a (...) familiar pluralism claiming many concepts are legitimate. Consequently, we must help biological facts determine grouphood, even when given a single grouping concept. (shrink)

The project of this paper is to understand what a phylogenetic tree represents and to discuss some of the implications that this has for the practice of systematics. At least the first part of this task, if not both parts, might appear trivial—or perhaps better suited for a single page in a textbook rather than a scholarly research paper. But this would be a mistake. While the task of interpreting phylogenetic trees is often treated in a trivial way, their interpretation (...) is tied to foundational conceptual questions at the heart of systematics—questions whose answers are hotly disputed. I have previously argued that widely shared ideas about the meaning and interpretation of phylogenetic trees are inconsistent with species concepts other than some genealogical version of a phylogenetic species concept (Velasco 2008). Here I rely on a similar approach and concentrate on the implications of the necessary conditions underlying the inferences that we make using phylogenetic trees. I argue that common practices for the interpretation and use of trees are in conflict and that unacceptable principles about species as units of phylogeny must be given up. According to the view that I will develop, all phylogenetic trees depict the history of populations. The branches on trees represent collections of population lineages through time and the splits represent population lineage splits. This is true regardless of whether the tips of the trees are themselves populations, or are species or higher taxa. Although this conclusion might be paired naturally with a view that species must be monophyletic groups, this population-centric view of trees is independent of that view of species. If we still want to have species that are paraphyletic groups of populations, this is permissible as long as we also do not treat species as the units of phylogeny. This population-centric view opposes a species-centric view of phylogeny and might be called a “rank-free” approach since it entails that we do not need to determine which groups are species (which is partly a ranking question) in order to build a tree. This conclusion and the argument for it are meant to be consistent with, but not require, acceptance of the conclusions of Velasco (2008) regarding species. (shrink)

Proposed here is that an overriding principle of nature governs all population behavior; that a single tenet drives the many regimes observed in nature—exponential-like growth, saturated growth, population decline, population extinction, and oscillatory behavior. The signature of such an all embracing principle is a differential equation which, in a single statement, embraces the entire panoply of observations. In current orthodox theory, this diverse range of population behaviors is described by many different equations—each with its own specific justification. Here, a single (...) equation governing all the regimes is proposed together with the principle from which it derives. The principle is: The effect on the environment of a population’s success is to alter that environment in a way that opposes the success. Experiments are suggested which could validate or refute the theory. Predictions are made about population behaviors. (shrink)

This paper aims to illustrate one of the primary goals of the philosophy of biology⎯namely, the examination of central concepts in biological theory and practice⎯through an analysis of the concepts of population and metapopulation in evolutionary biology and ecology. I will first provide a brief background for my analysis, followed by a characterization of my proposed concepts: the causal interactionist concepts of population and metapopulation. I will then illustrate how the concepts apply to six cases that differ in their population (...) structure; this analysis will also serve to flesh out and defend the concepts a bit more. Finally, I will respond to some possible questions that my analysis may have raised and then conclude briefly. (shrink)

In “‘Population’ is Not a Natural Kind of Kinds,” Jacob Stegenga argues against the claim that the concept of “population” is a natural kind and in favor of conceptual pluralism, ostensibly in response to two papers of mine (Millstein 2009, 2010). Pluralism is often an attractive position in the philosophy of science. It certainly is a live possibility for the concept of population in ecology and evolutionary biology, and I welcome the opportunity to discuss the topic further. However, I argue (...) that the case for conceptual pluralism has not yet been made. In what follows, I first clarify the issues at stake before taking up the topic of conceptual pluralism and responding to Stegenga’s criticisms of the causal interactionist population concept. (shrink)

Millstein argues against conceptual pluralism with respect to the definition of “population,” and proposes her own definition of the term. I challenge both Millstein’s negative arguments against conceptual pluralism and her positive proposal for a singular definition of population. The concept of population, I argue, does not refer to a natural kind; populations are constructs of biologists variably defined by contexts of inquiry.

Biologists studying ecology and evolution use the term “population” in many different ways. Yet little philosophical analysis of the concept has been done, either by biologists or philosophers, in contrast to the voluminous literature on the concept of “species.” This is in spite of the fact that “population” is arguably a far more central concept in ecological and evolutionary studies than “species” is. The fact that such a central concept has been employed in so many different ways is potentially problematic (...) for the reason that inconsistent usages (especially when the usage has not been made explicit) might lead to false controversies in which disputants are simply talking past one another. However, the inconsistent usages are not the only, or even the most important reason to examine the concept. If any set of organisms is legitimately called a “population,” selection and drift processes become purely arbitrary, too. Moreover, key ecological variables, such as abundance and distribution, depend on a nonarbitrary way of identifying populations. I sketch the beginnings of a population concept, drawing inspiration from the Ghiselin-Hull individuality thesis, and show why some alternative approaches are nonstarters. (shrink)

The target article excludes ancestral neutrality as a cause for the inheritance of schizophrenia, with an argument relating to selection against a single allele in the Finnish population. However, drift would predominate over selection within subisolates of the Finnish population. Comparisons of subisolates with heterogeneous populations may provide clues to the endophenotypic structure of complex polygenetic heritable mental disorders. (Published Online November 9 2006).

A study of stage structured model of fish population is presented. This model focuse on the anchovy population in the Bay of Biscay (Engraulis encrasicolus L.) is presented. The method of study is based on an intermediate complexity mathematical model, taking into account the spatialisation, the environmental conditions and the stage-structure of the fishes. First, to test the model, we show mathematical properties, such as unicity of the solution of structural stability. Then we provide numerical simulations, to validate the model (...) and to test the dynamics according to the variations of the parameters. (shrink)

Biological research on race has often been seen as motivated by or lending credence to underlying racist attitudes; in part for this reason, recently philosophers and biologists have gone through great pains to essentially deny the existence of biological human races. We argue that human races, in the biological sense of local populations adapted to particular environments, do in fact exist; such races are best understood through the common ecological concept of ecotypes. However, human ecotypic races do not in general (...) correspond with 'folk' racial categories, largely because many similar ecotypes have multiple independent origins. Consequently, while human natural races exist, they have little or nothing in common with 'folk' races. (shrink)

As the result of the complexity inherent in nature, mathematical models employed in ecology are often governed by a large number of variables. For instance, in the study of population dynamics we often deal with models for structured populations in which individuals are classified regarding their age, size, activity or location, and this structuring of the population leads to high dimensional systems. In many instances, the dynamics of the system is controlled by processes whose time scales are very different from (...) each other. Aggregation techniques take advantage of this situation to build a low dimensional reduced system from which behavior we can approximate the dynamics of the complex original system.In this work we extend aggregation techniques to the case of time dependent discrete population models with two time scales where both the fast and the slow processes are allowed to change at their own characteristic time scale, generalizing the results of previous studies. We propose a non-autonomous model with two time scales, construct an aggregated model and give relationship between the variables governing the original and the reduced systems. We also explore how the properties of strong and weak ergodicity, regarding the capacity of the system to forget initial conditions, of the original system can be studied in terms of the reduced system. (shrink)

The topic of population is treated only lightly in the major modern biographies of John Maynard Keynes, yet Keynes himself had strong - if varying - views on the subject. For many years he maintained a neo-Malthusian view of population, based on a postulated link between population growth and deteriorating terms of trade. This led him to take up a militant stance towards 'overpopulated' countries, notably India, China, and Egypt. Keynes on Population publishes two of John Maynard Keynes's manuscripts not (...) published in the Collected Writings: his Cambridge lectures on population and 1914 Oxford lecture on 'Population'. It provides a detailed commentary on the text of 'Population' and discusses the extent of Keynes's engagement with the Social Darwinist doctrine of the 'rapid multiplication of the unfit' and with eugenics. It then traces the subsequent vicissitudes of his views on population and his interventions in the contemporary politics of population. These include his part in the 1920s campaign for birth control, the reversal of his neo-Malthusianism, and his eventual support for family allowances. (shrink)

The word ``deme'' was coined by the botanists J.S.L. Gilmour and J.W.Gregor in 1939, following the pattern of J.S. Huxley's ``cline''. Its purposewas not only to rationalize the plethora of terms describing chromosomaland genetic variation, but also to reduce hostility between traditionaltaxonomists and researchers on evolution, who sometimes scorned eachother's understanding of species. A multi-layered system of compoundterms based on deme was published by Gilmour and J. Heslop-Harrison in1954 but not widely used. Deme was adopted with a modified meaning byzoologists (...) leading the evolutionary synthesis – Huxley, Simpson, Wright,and Mayr. Connections are shown between Gilmour's ideas around definingthe deme, his role in founding the Systematics Association, and his chapter``Taxonomy and Philosophy'' in the book The New Systematics. Thishistorical episode raises questions about the role of carefully-definedwords in scientific practice. (shrink)

Many studies have attempted to assess the relative effects of different vectors of a disease on animal populations. To this end, three measures have been proposed: Vectorial efficiency, Vectorial capacity and recently Vectorial effectiveness (or Vectorial impact). In this study we relate these measures to derive some of their properties emphasising in the vectorial impact for its importance in both, population performance of parasites and the proportion of the prevalence of one parasite due to a given vector. We applied the (...) quantitative expressions advanced in this study to a simple Chilean example with one parasite (Trypanosoma cruzi), two vectors (Triatoma infestans and Mepraia spinolai) and one animal population (humans: Chagas's disease). (shrink)

Two new modes of thinking have spread through systematics in the twentieth century. Both have deep historical roots, but they have been widely accepted only during this century. Population thinking overtook the field in the early part of the century, culminating in the full development of population systematics in the 1930s and 1940s, and the subsequent growth of the entire field of population biology. Population thinking rejects the idea that each species has a natural type (as the earlier essentialist view (...) had assumed), and instead sees every species as a varying population of interbreeding individuals. Tree thinking has spread through the field since the 1960s with the development of phylogenetic systematics. Tree thinking recognizes that species are not independent replicates within a class (as earlier group thinkers had tended to see them), but are instead interconnected parts of an evolutionary tree. It lays emphasis on the explanation of evolutionary events in the context of a tree, rather than on the states exhibited by collections of species, and it sees evolutionary history as a story of divergence rather than a story of development. Just as population thinking gave rise to the new field of population biology, so tree thinking is giving rise to the new field of phylogenetic biology. (shrink)

L'apparition, après 338, d'un nouvel élément d'origine topographique dans la façon de distinguer les citoyens n'a pas eu pour but de distinguer deux catégories de citoyens qui n'ont jamais existé. — Édition, en appendice, d'une double dédicace d'époque impériale votée par des tribus.

The Leslie matrix model (Leslie, 1945) for discrete population growth has been modified and used several times in population dynamics. A review is given of the basic model (n t + 1 = An t) and of its principal modifications. The modifications relating to the influences of internal or external factors to the population are studied with greater detail. The same applies to models where the population is divided in stages rather than in age classes.In the same line, Hadjibiros (1975, (...) 1976) studied a more general model, where the transition matrix corresponds to a population divided in stages of unequal duration, and where the time varying influences of the internal or external factors are included. This model offers the possibility of computer simulation of the population dynamics of a natural population represented by a demographic vector. (shrink)

In view of the confusion about the use of the term ‘population’ in biology, an analysis has been made of the use of the concept of population in biology. Origin and development, logic and epistemology of the population-concept have been investigated for that purpose. It appears that several concepts of population coexist in biology. The term ‘population’ is used for all these concepts, so it is not amazing that confusion has arisen. This confusion is the more dangerous, since ‘population’ plays (...) an important part in the theory of evolution. A modus has been suggested to diminish this confusion by defining ‘population’ in a very wide sense of the term and by proposing a ‘deme’—terminology to specify the various special concepts of population. (shrink)

I have attempted to clarify some of the pathways in the development of Darwin's thinking. The foregoing examples of influence by no means include all that can be found by comparing Darwin's writings with Humboldt's. However, the above examples seem adequate to show the nature and extent of this influence. It now seems clear that Humboldt not only, as had been previously known, inspired Darwin to make a voyage of exploration, but also provided him with his basic orientation concerning how (...) and what to observe and how to write about it. An important part of what Darwin assimilated from Humboldt was an appreciation of population analysis as a tool for assessing the state of societies and of the benefits and hardships which these societies can expect to receive from the living world around them.Darwin exhibited in his Journal of Researches a casual interest in the economic and political conditions of the countries he visited, but these considerations were much less important to him than to Humboldt. Instead, Darwin, with the assistance of Lyell's Principles of Geology, shifted from Humboldt's largely economic framework to a biological one built around the species question. This shift led Darwin away from a consideration of how the population biology of animals was related to man's economy to focus instead upon how population biology fitted into the economy of nature.Humboldt's Personal Narrative served very well as a model for Darwin's Journal of Researches, thereby helping Darwin gain scientific eminence. The Journal of Researches, like virtually all of Humboldt's writings, was a contribution to scientific orthodoxy. But Darwin had, along the way, acquired an urge to do more than just add his building blocks to the orthodox scientific edifice. He decided to rearrange those blocks of knowledge into a different structure, and for that task neither Humboldt's Personal Narrative nor any other of his works could serve as a model. Humboldt had lacked the confidence which Darwin needed that biogeography and the origin of species could be understood. Humboldt had not explored very far the possible connections between biology and geology. Nor had he provided a general synthetic account of population biology. Had he done so, he might have been more explicit about the extent of his endorsement of Malthus. But even if he had, Humboldt's strong orientation toward cooperation would probably have inhibited his recognition of the importance of competition in nature.Lyell, who had also benefited from reading Humboldt, gave Darwin insights that were lacking in Humboldt's Personal Narrative. Lyell admirably demonstrated how stratigraphy, paleontology, biogeography, and population biology could be interrelated, and his reasons for doing so were essentially the same as Darwin's. Lyell's understanding of biogeography and ecology came from the writings of Augustin-Pyramus de Candolle as much as from Humboldt's, and from the former Lyell derived an appreciation for the importance of competition and also a confidence that the mysteries of biogeography could be explained.117 Furthermore, Lyell's discussion of all these subjects and also of evolution in his Principles of Geology is a good synthetic argument that was the ideal model for Darwin's greatest book.Darwin, having become convinced that species change through time, was able to synthesize in his mind the contributions which he had derived from the writings of Humboldt and Lyell as they applied to the species question. When Darwin wrote his Journal of Researches there were two large gaps in his thinking about evolution that bothered him—the mechanism of evolution and the causes of extinction. It was only after reading Malthus in 1838 that he realized, as Lyell had more or less pointed out, how important was competition in nature. He now had the general outlines for his theory, and in the 1845 abridged edition of his Journal, now retitled The Voyage of the Beagle, he inserted a fuller discussion of competition in nature which showed his awareness of its importance as an ecological factor.118. (shrink)

Darwin's theory of evolution brought to an end the static view of nature. It was no longer possible to think of species as immortal, with secure places in nature. Fluctuation of population could no longer be thought of as occurring within definite limits which had been set at the time of creation. Nor was it any longer possible to generalize from the differential reproductive potentials, or from a few cases of mutualism between species, that everything in nature was “fitted to (...) produce general ends, and reciprocal uses.” 134 The appeal to “design” could no longer be substituted for answers to questions concerning animal demography. Instead, the dynamics of a population had to be viewed as the outcome of species' struggle against animate and inanimate factors in the environment. Both the members of a species and the environmental factors tend to vary randomly, and therefore neither evolution nor population dynamics could be fully understood alone. For this reason Darwin's linking of the two subjects was inevitable and not merely an historical accident. Since Darwin had shown that no automatic equilibrium existed, he demonstrated the importance of closer study of the causes of population dynamics and extinction. He also indicated that an understanding of population depends upon the development of a broad knowledge in ecology.Viewed from another direction, Darwin's work ended the early modern era of population studies by clarifying three interrelated problems which were important for understanding population: extinction, distribution, and the nature of species. The components of his answer had been discussed in the eighteenth century, but there had not existed enough evidence for the completion of the revolution in thought which had then begun. At the beginning of the nineteenth century, Playfair found the evidence for extinction conclusive, and, in spite of Lamarck, Curvier convinced the scientific world that there could no longer be any doubt about it. This was a step the importance of which, with his limited knowledge of biogeography and population, Cuvier could not have fully realized. Lamarck attempted, with his evolutionary theory, to circumvent the necessity for admitting extinction, but he overestimated the adaptability of organisms and in doing so he underestimated the importance of competition and the whole field of ecology. On the other hand, he was not willing to let questions such as the origin of species remain taboo to science. The origin of species was a biogeographical as well as a paleontological question. Humboldt correlated environment with the distribution of species and conveyed the impression that plant communities are subject to change. De Candolle, following the lead of Linnaeus and Humboldt, emphasized the ecological aspects of biogeography, not only the importance of habitat and range, clearly showing the ecological effects of competition. The entomologists Kirby and Spence took a faltering step toward understanding the relationship between population and ecological role, but they fell short of any significant new conclusions. Neither they nor Swainson could fully comprehend the new perspective of De Candolle.Lyell was able to bring together the evidence from these three lines of investigation and weave them into an important synthesis that almost accomplished that Darwin later did. Although opposing Lamarck's theory of evolution, Lyell had a dynamic view of ecology. He realized that population dynamics offered an important key to the understanding of biogeography. Since he knew that species become extinct, he investigated closely the factors which could either preserve or extinguish species. While explaining these factors, he described the interrelationships of species in greater detail than had ever been done before. Forbes continued to develop Lyell's ecological concepts, and his first-hand field experience enabled him to describe biotic communities more concretely than Lyell had.Having the advantages of Lyell's understanding and his own experience from a global voyage, Darwin could take the final step from the static to the dynamic concept of life. He had seen populations fluctuating and also fossil species in South America, and on the Galapagos Islands he had encountered a biogeographical problem that could not be credibly solved without the idea of evolution. However, the bare idea of evolution did not fully answer his questions. He sought physiological causes of extinction before he read Malthus and realized that De Candolle and Lyell had correctly emphasized the importance of competition. Darwin found that, in order to understand evolution, he needed to improve his understanding of ecology. He wanted to know when populations were most easily decimated, how extensive were competition and cooperation, what effects parasites have upon populations, and what changes occur in biotic communities when a species is either added or subtracted. He contributed to some extent to answering these questions. Though there remained much for others to do, there was now a new and more secure theoretical framework within which later studies could be interpreted. As Ernst Mayr has observed, Darwin's “consistent thinking in terms of population has had an impact on biological theory and practice which is second only to his sponsorship of natural selection as the mechanism of evolution.” 135. (shrink)

The term typology has been used in taxonomy to imply procedures and philosophies of somewhat diverse meanings. Not all typological work meets every criterion suggested for such work by various authors. Some of these criteria are untenable when viewed in the context of modern biological theory, while others seem eminently reasonable in the light of present day knowledge. Mere reference to a work as typological will not convey to the reader or listener a clear idea why a reviewer has decided (...) that it merits the term. Similarly, it would be improper to attach automatic derogatory implications to the adjective “typological”, since it is only those aspects of typological procedure which cannot be defended or maintained today that would merit such a connotation. The classificatory philosophy of many proponents of typology is based on a platonic idealism. To consider a taxonomic type as an abstract idea seems of doubtful utility at best and is certainly beyond the realm of scientific inquiry. The method by which types are obtained must be indicated without ambiguity. In classical typological work this is generally not done, and reconstructions relying on the metamorphosis of parts are often rather vague and controversial. Similarly, abstractions relying either on weighted or unweighted averages of the characters in the taxa to be studied are of questionable value. It would appear that character variation of individuals within taxa or of taxa within higher taxa must in some way be accounted for, if types are to be defined which will represent the natural order in the system. The choice of characters must also be clearly defined and defensible. A priori weighting or preference of some characters over others, based on either presumed phylogenetic importance or logical or functional primacy, is an unjustifiable procedure. Equal weighting and use of all characters leads directly into an empirical approach, which attempts to classify organisms on the basis of all available evidence, without preconceived notions about their arrangement. Such a procedure also arrives at a classification from which types may be abstracted, but does so by clearly defined and previously determined criteria, and does not rely on hypotheses based on certain preliminary conclusions in order to reinforce its argument. The empirical approach, the most notable example of which in recent years has been the development of numerical taxonomy, has definite typological aspects which, however, appear to this writer to be of value and preferable to the phylogenetic method. Smirnov's statistical method of constructing types is contrasted with results obtained by numerical taxonomy. The latter appear preferable from several points of view. (shrink)