Speciation

Abstract The quasispecies theory is a helpful concept in the explanation of RNA virus evolution and behaviour, with a relevant impact on methods used to fight viral diseases. It has undergone some adaptations to integrate new empirical data, especially the non-deterministic nature of mutagenesis, and the variety of behavioural motifs in cooperation, competition, communication, innovation, integration, and exaptation. Also, the consortial structure of quasispecies with complementary roles of memory genomes of minority populations better fits the empirical data than did the (...) original concept of a master sequence and its mutant spectra. The high productivity of quasispecies variants generates unique sequences that never existed before and will never exist again. In the present essay, we underline that such sequences represent really new ontological entities, not just error copies of previous ones. Their primary unique property, the incredible variant production, is suggested here as quasispecies productivity, which replaces the error-replication narrative to better fit into a new relationship between mankind and living nature in the twenty-first century. (shrink)

Katz denies that organisms created in a lab as part of a de-extinction attempt will be authentic members of the extinct species, on the basis that they will lack the original species’ defining biological and evolutionary history. Against Katz, I note that an evolutionary lineage is conferred on an organism through its inheriting genes from forebears already possessed of such a lineage, and that de-extinction amounts to a delayed, human-assisted reproductive process, in which genes are inherited from forebears long dead. (...) My conclusion is that de-extinct organisms can perfectly well have an ancient evolutionary history, contrary to what Katz claims. (shrink)

An artwork in one culture and form, say European classical music, cannot be evaluated in the context of another, say Hindustani music. While a person educated in the traditions of European music can rationally evaluate and discuss her response to a string quartet by Beethoven, her response to music in a foreign culture is merely subjective. She might "like" the latter, but her response is merely subjective. In this paper, I discuss the role of artforms: why response can be "objectively" (...) discussed within artforms, but is nonetheless subjective across them. My discussion falls into two parts. First, I offer a psychological account of aesthetic response to art: cultural learning stabilizes this response across individuals who are educated in an artform. Second, I offer a cultural-evolutionary account of the diversity of artforms, adapting Darwin's Principle of the Divergence of Character to explain the multiplicity of art forms. (shrink)

This paper proposes a new and testable view about the nature of species and other evolving lineages, according to which they are feedback systems. On this view, it is a mistake to think gene flow, niche sharing, and trait frequency similarities between populations are among variables that interact to cause some further downstream variable that distinguishes evolving lineages from each other, some sort of “species cohesion” for example. Instead, gene flow, niche sharing, similarities between populations, and other causal variables feed (...) into each other—instances of these at earlier times help cause instances of these same variables at later times. And any lineage-identifying cohesion just is the recurrence or cycling of these feedback relations within metapopulations over generations. Such cohesion can then be represented as variable M within multi-dimensional variable spaces, where values of M vary dynamically with the frequency and magnitude of feedback relations. Related conditions for being a species or other evolving lineage are then clarified. To argue for the development and testing of this view, the paper shows how it improves upon others. (shrink)

This editorial introduces a series of review articles concerning the ways in which recent work on microbial evolution has both deepened and challenged the modern synthesis. The authors develop a framework for thinking about theory change in biology.

All the conserved detailed results of evolution stored in DNA must be read, transcribed, and translated via an RNAmediated process. This is required for the development and growth of each individual cell. Thus, all known living organisms fundamentally depend on these RNA-mediated processes. In most cases, they are interconnected with other RNAs and their associated protein complexes and function in a strictly coordinated hierarchy of temporal and spatial steps (i.e., an RNA network). Clearly, all cellular life as we know it (...) could not function without these key agents of DNA replication, namely rRNA, tRNA, and mRNA. Thus, any definition of life that lacks RNA functions and their networks misses an essential requirement for RNA agents that inherently regulate and coordinate (communicate to) cells, tissues, organs, and organisms. The precellular evolution of RNAs occurred at the core of the emergence of cellular life and the question remained of how both precellular and cellular levels are interconnected historically and functionally. RNA-networks andRNA-communication can interconnect these levels.With the reemergence of virology in evolution, it became clear that communicating viruses and subviral infectious genetic parasites are bridging these two levels by invading, integrating, coadapting, exapting, and recombining constituent parts in host genomes for cellular requirements in gene regulation and coordination aims. Therefore, a 21st century understanding of life is of an inherently social process based on communicating RNA networks, in which viruses and cells continuously interact. (shrink)

Starting with Aristotle and moving on to Darwin, Marco Solinas outlines the basic steps from the birth, establishment and later rebirth of the traditional view of living beings, and its overturning by evolutionary revolution. The classic framework devised by Aristotle was still dominant in the 17th Century world of Galileo, Harvey and Ray, and remained hegemonic until the time of Lamarck and Cuvier in the 19th Century. Darwin's breakthrough thus takes on the dimensions of an abandonment of the traditional finalistic (...) theory. It was a transition exemplified in the morphological analysis of useless parts, such as the sightless eyes of moles, already discussed by Aristotle, which Darwin used as a crowbar to unhinge the systematic recourse to final causes. With many excerpts, a chronological sequence and an analytical approach, this book follows the course of the two conceptions that have shaped the destiny of life sciences in western culture. (shrink)

Intermediary metabolism molecules are orchestrated into logical pathways stemming from history (L-amino acids, D-sugars) and dynamic constraints (hydrolysis of pyrophosphate or amide groups is the driving force of anabolism). Beside essential metabolites, numerous variants derive from programmed or accidental changes. Broken down, variants enter standard pathways, producing further variants. Macromolecule modification alters enzyme reactions specificity. Metabolism conform thermodynamic laws, precluding strict accuracy. Hence, for each regular pathway, a wealth of variants inputs and produces metabolites that are similar to but not (...) the exact replicas of core metabolites. As corollary, a shadow, paralogous metabolism, is associated to standard metabolism. We focus on a logic of paralogous metabolism based on diversion of the core metabolic mimics into pathways where they are modified to minimize their input in the core pathways where they create havoc. We propose that a significant proportion of paralogues of well-characterized enzymes have evolved as the natural way to cope with paralogous metabolites. A second type of denouement uses a process where protecting/deprotecting unwanted metabolites - conceptually similar to the procedure used in the laboratory of an organic chemist - is used to enter a completely new catabolic pathway. (shrink)

Darwin's “mystery of mysteries,” the origin of species, is caused by the evolution of speciation phenotypes, i.e. phenotypic differences that depress gene flow between daughter species during speciation. Postmating, prezygotic (PMPZ) differentiation characterizes many closely related species causing conspecific sperm precedence (CSP), wherein a female preferentially utilizes conspecific over heterospecific sperm in fertilization. Until recently, the components of CSP have been difficult to observe and study in internally fertilizing organisms. Research into the mechanisms of CSP is now progressing rapidly with (...) the help of new innovative research tools. With the recent development of a sperm labeling system enabling distinct labels for different males, direct observations of competing male sperm within the female reproductive tract are possible, revealing multiple PMPZ phenotypes that combine to cause CSP. The discovery of mechanisms underlying CSP predicts an exciting future for studies of PMPZ speciation phenotypes and possible general principles underlying the origin of species. (shrink)

Graphical AbstractSquamates may be an attractive group in which to study the influence of sex chromosomes on speciation rates because of the repeated evolution of heterogamety (both XY and ZW), as well as an apparently large number of taxa with environmental sex-determination.

The book aims to offer a contribution to the historiographical and conceptual reconfiguration of the evolutionary revolution in the light of the centuries-old tenets of the Aristotelian biological tradition. Darwin’s breakthrough constitutes a thorough overturning of the fixist, essentialist and teleological framework created by Aristotle, a framework still dominant in the 17th Century world of Harvey and Ray, as well as Galileo, and then hegemonic until Linnaeus and Cuvier. This change is exemplified in the morphological analysis of useless parts, such (...) as the sightless eyes of moles, already discussed by Aristotle, and which Darwin used almost like a crowbar to unhinge the systematic recourse to final causes. This is an ancient teleological heritage present in various forms in the concept of natural selection, but by then confined within an eminently historical framework open to randomness. Un contributo alla riconfigurazione storiografica e concettuale della rivoluzione evoluzionistica alla luce della tenuta plurisecolare della tradizione biologica aristotelica. La svolta di Darwin si delinea quale puntuale rovesciamento dell'impianto fissista, essenzialista e teleologico coniato da Aristotele, ancora dominante nel Seicento di Harvey e di Ray, nonostante Galileo, e poi egemone fino a Linneo e Cuvier. Svolta esemplificata dall'analisi morfologica delle parti inutili, come gli occhi ciechi della talpa, tematizzate già da Aristotele, e che Darwin usò quale grimaldello per scardinare il ricorso sistematico alle cause finali. Antica eredità teleologica presente in varie forme nel concetto di selezione naturale, ma ormai calata entro una griglia eminentemente storica e aperta alla casualità. (shrink)

Tom Stoppard’s 1966 play (and 1990 movie) /Rosencrantz and Guildenstern are Dead/ is a metatext – as a text, it interprets, builds upon, and refers to another text, Shakespeare’s Hamlet. Similarly, David N. Reznick’s /The Origin then and now: An interpretative guide to the Origin of Species/ (Princeton UP, 2010) is also a metatext. In this review, I turn to the history of science to evaluate whether Reznick’s book shares three families of virtues with Stoppard’s play: (i) brevity and precision, (...) (ii) intrigue and appeal, and (iii) a genuine value-add to the original. (shrink)

Several features of the yeast mitochondrial genome, including high mutation rate, dynamic genomic structure, small effective population size, and dispensability for cellular viability, make it a promising candidate for generating hybrid incompatibility and driving speciation. Cytonuclear incompatibility, a specific type of Dobzhansky‐Muller genetic incompatibility caused by improper interactions between mitochondrial and nuclear genomes, has previously been observed in a variety of organisms, yet its role in speciation remains obscure. Recent studies in Saccharomyces yeast species provide a new insight, with experimental (...) evidence that cytonuclear incompatibility and DNA sequence divergence are both causes of the reproductive isolation of different yeast species. Interestingly, these two mechanisms seem to be perfectly complementary to each other in terms of their effects and evolutionary trajectories. Direct molecular analyses of the incompatible genes in yeasts have started to shed light on the evolutionary forces driving speciation. Editor's suggested further reading in BioEssaysThe cytoplasmic structure hypothesis for ribosome assembly, vertical inheritance, and phylogeny AbstractMitochondrial bioenergetics as a major motive force of speciation Abstract. (shrink)

The Tree of Life hypothesis frames the evolutionary process as a series of events whereby lineages diverge from one another, thus creating the diversity of life as descendent lineages modify properties from their ancestors. This hypothesis is under scrutiny due to the strong evidence for lateral gene transfer between distantly related bacterial taxa, thereby providing extant taxa with more than one parent. As a result, one argues, the Tree of Life becomes confounded as the original branching structure is gradually superseded (...) by reticulation, ultimately losing its ability to serve as a model for bacterial evolution. Here we address a more fundamental issue: is there a Tree of Life that results from bacterial evolution without considering such lateral gene transfers? Unlike eukaryotic speciation events, lineage separation in bacteria is a gradual process that occurs over tens of millions of years, whereby genetic isolation is established on a gene-by-gene basis. As a result, groups of closely related bacteria, while showing robust genetic isolation as extant lineages, were not created by an unambiguous series of lineage-splitting events. Rather, a temporal fragmentation of the speciation process results in cognate genes showing different genetic relationships. We argue that lineage divergence in bacteria does not produce a tree-like framework, and inferences drawn from such a framework have the potential to be incorrect and misleading. Therefore, the Tree of Life is an inappropriate paradigm for bacterial evolution regardless of the extent of gene transfer between distantly related taxa. (shrink)

Weismann's ideas on species transmutation were first expressed in his famous debate with Moritz Wagner on the mechanism of speciation. Wagner suggested that the isolation of a colony from its original source is a preliminary and necessary factor for speciation. Weismann accepted a secondary, facilitating role for isolation, but argued that natural and sexual selection are the primary driving forces of species transmutation, and are always necessary and often sufficient causes for its occurrence. The debate with Wagner, which occurred between (...) 1868 and 1872 within the framework of Darwin's discussions of geographical distribution, was Weismann's first public battle over the mechanism of evolution. This paper, which offers the first comprehensive analysis of this debate, extends previous analyses and throws light on the underlying beliefs and motivations of these early evolutionists, focusing mainly on Weismann's views and showing his commitment to what he later called "the all sufficiency of Natural Selection." It led to the crystallization of his ideas on the central and essential role of selection, both natural and sexual, in all processes of evolution, and, already at this early stage in his theoretical thinking, was coupled with sophisticated and nuanced approach to biological organization. The paper also discusses Ernst Mayr's analysis of the debate and highlights aspects of Weismann's views that were overlooked by Mayr and were peripheral to the discussions of other historians of biology. (shrink)

Mitochondrial bioenergetics plays a key role in multiple basic cellular processes, such as energy production, nucleotide biosynthesis, and iron metabolism. It is an essential system for animals' life and death (apoptosis) and it is required for embryo development. This, in conjunction with its being subjected to adaptive processes in multiple species and its gene products being involved in the formation of reproductive barriers in animals, raises the possibility that mitochondrial bioenergetics could be a candidate genetic mechanism of speciation. Here, we (...) discuss genetic and biochemical evidence for the possible involvement of this unique system, encoded by two genomes (the mitochondrial and nuclear genomes), that differ by an order of magnitude in their mutation rates in processes leading to speciation events. (shrink)

Standard biological and philosophical treatments assume that dramatic genotypic or phenotypic change constitutes instantaneous speciation, and that barring such saltation, speciation is gradual evolutionary change in individual properties. Both propositions appear to be incongruent with standard theoretical perspectives on species themselves, since these perspectives are (a) non-pheneticist, and (b) tend to disregard intermediate cases. After reviewing certain key elements of such perspectives, it is proposed that species-membership is mediated by membership in a population. Species-membership depends, therefore, not on intrinsic characteristics (...) of an organism, but on relationship of an organism to others. A new definition of speciation is proposed in the spirit of this proposal. This definition implies that dramatic change is neither necessary nor sufficient for speciation. It also implies, surprisingly, that an organism can change species during its lifetime. (shrink)

I begin with a description of the benefits and limits of DNA barcoding as presented by its advocates not its critics. Next, I argue that due to the mutually dependent relationship between defining and delimiting species, all systems of classification are grounded in theory, even if only implicitly. I then proceed to evaluate DNA barcoding in that context. In particular, I focus on the barcoders’ use of a sharp boundary by which to delimit species, arguing that this boundary brings along (...) additional theoretical commitments inconsistent with the way taxonomists conceive of species, viz., as entities that have vague boundaries and that cannot be defined by any single attribute other than ancestry. Given these inconsistencies, I conclude that even if groupings based on DNA barcodes match those of an existing taxonomy, the two systems of classification are not necessarily tracking the same entities, i.e., species. (shrink)

Selectionist evolutionary theory has often been faulted for not making novel predictions that are surprising, risky, and correct. I argue that it in fact exhibits the theoretical virtue of predictive capacity in addition to two other virtues: explanatory unification and model fitting. Two case studies show the predictive capacity of selectionist evolutionary theory: parallel evolutionary change in E. coli, and the origin of eukaryotic cells through endosymbiosis.

Using ideas from evolution and postformal stages of hierarchical complexity, a hypothetical scenario, premised on genetic engineering advances, portrays the development of a new humanoid species, Superions. How would Superions impact and treat current humans? If the Superion scenario came to pass, it would be the ultimate genocidal terrorism of eliminating an entire species, Homo Sapiens. We speculate about defenses Homo Sapiens might mount. The tasks to relate two species (systems) constitutes a postformal, Metasystematic task. Developing a system of discourse (...) to prevent destruction requires postformal Paradigmatic-stage tasks. Implications are twofold: species survival and sufficient evolution to survive. (shrink)

(2008). Genetic Engineering and the Speciation of Superions from Humans. World Futures: Vol. 64, Postformal Thought and Hierarchical Complexity, pp. 436-443.

Richard Goldschmidt famously rejected the notion of atomic and corpuscular genes, arranged on the chromosome like beads-on-a-string. I provide an exegesis of Goldschmidt’s intuition by analyzing his repeated and extensive use of metaphorical language and analogies in his attempts to convey his notion of the nature of the genetic material and specifically the significance of chromosomal pattern. The paper concentrates on Goldschmidt’s use of metaphors in publications spanning 1940-1955. -/- .

Genes that exert their function when they are introduced into a foreign genetic background pose many questions to our current understanding of the forces and mechanisms that promote either the maintenance or divergence of gene functions over evolutionary time. The melanoma inducing Xmrk oncogene of the Southern platyfish (Xiphophorus maculatus) is a stable constituent of the genome of this species. It displays its tumorigenic function, however, almost exclusively only after inter‐populational or, even more severely, interspecific hybridization events. The Xiphophorus hybrid (...) melanoma system has gained attention in biomedical research as a genetic model for studying tumor formation. From an evolutionary perspective, a prominent question is: how could this gene persist over millions of years? An attractive hypothesis is that Xmrk, acting as a detrimental gene in a hybrid genome, could be a speciation gene that shields the gene pool of its species from mixing with other closely related sympatric species. In this article, I briefly review our current knowledge of the molecular genetics and biochemical functions of the Xmrk gene and discuss aspects of its evolutionary history and presence with respect to this idea. While Xmrk as a potentially injurious oncogene has clearly survived for millions of years, its role as a speciation gene has to be questioned. BioEssays 30:822–832, 2008. © 2008 Wiley Periodicals, Inc. (shrink)

A founder event occurs when a new population is established from a small number of individuals drawn from a large ancestral population. Mayr proposed that genetic drift in an isolated founder population could alter the selective forces in an epistatic system, an observation supported by recent studies. Carson argued that a period of relaxed selection could occur when a founder population is in an open ecological niche, allowing rapid population growth after the founder event. Selectable genetic variation can actually increase (...) during this founder‐flush phase due to recombination, enhanced survival of advantageous mutations, and the conversion of non‐additive genetic variance into additive variance in an epistatic system, another empirically confirmed prediction. Templeton combined the theories of Mayr and Carson with population genetic models to predict the conditions under which founder events can contribute to speciation, and these predictions are strongly confirmed by the empirical literature. Much of the criticism of founder speciation is based upon equating founder speciation to an adaptive peak shift opposed by selection. However, Mayr, Carson and Templeton all modeled a positive interaction of selection and drift, and Templeton showed that founder speciation is incompatible with peak‐shift conditions. Although rare, founder speciation can have a disproportionate importance in adaptive innovation and radiation, and examples are given to show that “rare” does not mean “unimportant” in evolution. Founder speciation also interacts with other speciation mechanisms such that a speciation event is not a one‐dimensional process due to either selection alone or drift alone. BioEssays 30:470–479, 2008. © 2008 Wiley Periodicals, Inc. (shrink)

Pierre Trémaux’s 1865 ideas on speciation have been unjustly derided following his acceptance by Marx and rejection by Engels, and almost nobody has read his ideas in a charitable light. Here we offer an interpretation based on translating the term sol as “habitat”, in order to show that Trémaux proposed a theory of allopatric speciation before Wagner and a punctuated equilibrium theory before Gould and Eldredge, and translate the relevant discussion from the French. We believe he may have influenced Darwin’s (...) revision to the third edition of the Origin on rates of evolution, and suggest that Gould’s dismissal of Trémaux is motivated by concern that others might think punctuated equilibrium theory was tainted by a connection with Trémaux. (shrink)

Speciation is an aspect of evolutionary biology that has received little philosophical attention apart from articles mainly by biologists such as Mayr (1988). The role of speciation as a terminus a quo for the individuality of species or in the context of punctuated equilibrium theory has been discussed, but not the nature of speciation events themselves. It is the task of this paper to attempt to bring speciation events into some kind of general scheme, based primarily upon the work of (...) Sergey Gavrilets on adaptive landscapes, using migration rate, or gene flow, as the primary scale, and concluding that adaptive and drift explanations are complementary rather than competing. I propose a distinction between intrinsic and extrinsic selection, and the notion of reproductive reach and argue that speciation modes should be discriminated in terms of gene flow, the nature of selection maintaining reproductive reach, and whether the predominant cause is selective or stochastic. I also suggest that the notion of an adaptive “quasispecies” for asexual species is the primitive notion of species, and that members of reproductively coherent sexual species are additionally coadapted to their mating partners. (shrink)

Recent discussion of mechanism has suggested new approaches to several issues in the philosophy of science, including theory structure, causal explanation, and reductionism. Here, I apply what I take to be the fruits of the Ônew mechanical philosophyÕ to an analysis of a contemporary debate in evolutionary biology about the role of natural selection in speciation. Traditional accounts of that debate focus on the geographic context of genetic divergence— namely, whether divergence in the absence of geographic isolation is possible (or (...) significant). Those accounts are at best incomplete, I argue, because they ignore the mechanisms producing divergence and miss what is at stake in the biological debate. I argue that the biological debate instead concerns the scope of particular speciation mechanisms which assign different roles to natural selection at various stages of divergence. The upshot is a new interpretation of the crux of that debate—namely, whether divergence with gene flow is possible (or significant) and whether the isolating mechanisms producing it are adaptive. Ó 2005 Elsevier Ltd. All rights reserved. (shrink)

Recent discussion of mechanism has suggested new approaches to several issues in the philosophy of science, including theory structure, causal explanation, and reductionism. Here, I apply what I take to be the fruits of the 'new mechanical philosophy' to an analysis of a contemporary debate in evolutionary biology about the role of natural selection in speciation. Traditional accounts of that debate focus on the geographic context of genetic divergence--namely, whether divergence in the absence of geographic isolation is possible (or significant). (...) Those accounts are at best incomplete, I argue, because they ignore the mechanisms producing divergence and miss what is at stake in the biological debate. I argue that the biological debate instead concerns the scope of particular speciation mechanisms which assign different roles to natural selection at various stages of divergence. The upshot is a new interpretation of the crux of that debate--namely, whether divergence with gene flow is possible (or significant) and whether the isolating mechanisms producing it are adaptive. (shrink)

Roderic Page’s new book, Tangled Trees: Phylogeny, Cospeciation and Coevolution (2003), is a worthwhile read for anyone interested in either methodological issues in systematics, or how organisms shape one another’s selective environments. “Cospeciation,” for the uninitiated, is the concurrent speciation of two or more lineages that are ecologically associated (e.g. host-parasite associations, as well as mutualistic or symbiotic associations). “Coevolution,” in contrast, is the reciprocal adaptation of hosts and parasite taxa. The main focus of Page’s book is thus when, how (...) and why the branching process of host taxa mirrors that of parasite taxa. “Parasite” here is broadly conceived to be anything from a louse to a virus to a retrotransposon, and “host” may be anything from a genome to a whale. (shrink)

Intellectual and professional reforms in evolutionary studies between 1935 and 1950 included substantial expansion, diversification, and realignment of community infrastructure. Theodosius Dobzhansky, Julian Huxley and Alfred Emerson organized the Society for the Study of Speciation at the 1939 AAAS Columbus meeting as one response to concerns about ‘isolation’ and ‘lack of contact’ among speciation workers worried about ‘dispersed’ and ‘scattered’ resources in this newly robust ‘borderline’ domain. Simply constructed, the SSS sought neither the radical reorganization of specialities nor the creation (...) of some new discipline. Instead, it was designed to facilitate: to simplify exchange of information and to provide a minimally invasive avenue for connecting disparate researchers. Emerson served as SSS secretary and was its principal agent. After publishing one block of publications, however, the SSS became ‘quiescent’. Anxious to promote his own agenda, Ernst Mayr tried to manoeuvre around Emerson in an effort to revitalize the project. After meeting impediments, he moved his efforts elsewhere. The SSS was too short-lived to merit a claim for major impact within the community; however, it reveals important features of community activity during the synthesis period and stands in contrast to later efforts by George Simpson, Dobzhansky, and Mayr. (shrink)

Numerous concepts exist for biological species. This diversity of ideas derives from a number of sources ranging from investigative study of particular taxa and character sets to philosophical aptitude and world view to operationalism and nomenclatorial rules. While usually viewed as counterproductive, in reality these varied concepts can greatly enhance our efforts to discover and understand biological diversity. Moreover, this continued "turf war" and dilemma over species can be resolved if the various concepts are viewed in a hierarchical system and (...) each evaluated for its inherent level of consilience. Under this paradigm a theoretically appropriate, highly consilient concept of species capable of colligating the abundant types of species diversity offers the best guidance for developing and employing secondary operational concepts for identifying diversity. Of all the concepts currently recognized, only the non-operational Evolutionary Species Concept corresponds to the requisite parameters and, therefore, should serve as the theoretical concept appropriate for the category Species. As operational concepts, the remaining ideas have been incompatible with one another in their ability to encompass species diversity because each has restrictive criteria as to what qualifies as a species. However, the operational concepts can complement one another and do serve a vital role under the Evolutionary Species Concept as fundamental tools necessary for discovering diversity compatible with the primary theoretical concept. Thus, the proposed hierarchical system of primary and secondary concepts promises both the most productive framework for mutual respect for varied concepts and the most efficient and effective means for revealing species diversity. (shrink)

A significant proportion of conservationists' work is directed towards efforts to save disappearing species. This relies upon the belief that species extinction is undesirable. When justifications are offered for this belief, they very often rest upon the assumption that extinction brought about by humans is different in kind from other forms of extinction. This paper examines this assumption and reveals that there is indeed good reason to suppose current anthropogenic extinctions to be different in kind from extinctions brought about at (...) other times or by other factors. Having considered – and rejected – quantity and rate of extinction as useful distinguishing factors, four alternative arguments are offered, each identifying a way in which anthropogenic extinction is significantly different from other forms of extinction, even mass extinction: (1) Humans are a different kind of natural cause from other causes of extinction; (2) Extinctions brought about by humans are uniquely persistent; (3) Anthropogenic extinctions are effectively random whereas past mass extinctions are rule-bound; (4) The impact of the current anthropogenic extinction event differs from the impact of other extinction events of the past, such that future recovery may not follow past patterns. Together, these four arguments suggest that the present-day extinction event brought about by humans may be unprecedented and that we cannot clearly extrapolate from past to present recovery from extinctions. Although insufficient as justification for the claim that present-day extinctions are undesirable, the arguments provide some ammunition for conservationists' conviction that species extinction – in which humans play an accelerating role – ought to be prevented. (shrink)

The scientific legacy of Karl Pearson and his role as one of the principal architects of the modern theory of mathematical statistics, has generated enough interest to have created an intellectual enterprise on various aspects of his life and work. Despite this interest, Pearson's earliest and most formative statistical work which he delivered in thirty of his thirty-eight Gresham lectures from 17 November 1891 to 11 May 1894 has, to date, been given very little consideration. Pearson is perhaps, best known (...) to historians of science for his first eight Gresham lectures, delivered in London in February and May, 1891, on ‘The Scope and Method of Modern Science’, as these lectures were published with modification in theGrammar of Sciencein 1892. The only discussions which have emerged from some of the other thirty lectures have come from Egon Pearson and Steve Stigler. As the great bulk of these lectures have not been fully utilized, previous attempts to identify the impetus to his statistical work have been derived either from his teaching of correlation at University College London in 1895–96 or from his third statistical paper which, in part, addresses Francis Galton's work on simple correlation and simple regression. In spite of the emphasis on Galton's work on simple correlation and regression, little attention has been given to Pearson's more innovative work in that paper, which includes his development of the following statistical methods: multiple correlation, multiple regression, the standard error of estimate, the coefficient of variation and the use of determinantal matrix algebra for biometrical methods. This use of a higher form of algebra not only provided a most striking departure from earlier forms and uses of statistics, but it led to an increasing specialization in the emerging discipline of ‘mathematical statistics’. (shrink)

Biomedical researchers claim there is significant biomedical information about humans which can be discovered only through experiments on intact animal systems (AMA p. 2). Although epidemiological studies, computer simulations, clinical investigation, and cell and tissue cultures have become important weapons in the biomedical scientists' arsenal, these are primarily "adjuncts to the use of animals in research" (Sigma Xi p. 76). Controlled laboratory experiments are the core of the scientific enterprise. Biomedical researchers claim these should be conducted on intact biological systems, (...) whole animals. By observing the effects of various stimuli in non-human animals, we can form legitimate expectations about the likely effects of these stimuli in humans. Perhaps more importantly, we can understand the biomedical condition's causal mechanisms. (shrink)

Claude Bernard, the father of scientific physiology, believed that if medicine was to become truly scientiifc, it would have to be based on rigorous and controlled animal experiments. Bernard instituted a paradigm which has shaped physiological practice for most of the twentieth century. ln this paper we examine how Bernards commitment to hypothetico-deductivism and determinism led to (a) his rejection of the theory of evolution; (b) his minima/ization of the role of clinical medicine and epidemiological studies; and (c) his conclusion (...) that experiments on nonhuman animals were, "entirely conclusive for the toxicology and hygiene of man". We examine some negative consequences of Bernardianism for twentieth century medicine, and argue that physio/ogy's continued adherence to Bernardianism has caused it to diverge from the other biological sciences which have become increasingly infused with evolutionary theory. (shrink)

The crucial phase of speciation is argued to be the evolution of mating cross-incompatibility (prezygotic incompatibility) between the genotypes distinguishing the prospective species populations. Based on this idea, a single-locus model of speciation is presented, which is shown to be biologically plausible and may help to settle the controversy as to the biological significance of single-locus modes of speciation. The model involves three alleles, two of which characterize in homozygous state the prospective species populations and in heterozygous state their hybrids. (...) The third allele represents a mutant which is equivalent to one of the first two alleles with the exception that it inhibits mating with carriers of the third allele. This third allele is fixed in one population and immigrates into a second population which contains the mutant inhibiting matings with members of the former population. Migration in the reverse direction does not occur. Proceeding from a widely applicable concept of fitness and mating preference it is shown that postzygotic incompatibility (hybrid or heterozygote disadvantage) alone suffices to trigger evolutionary replacement of the extant mating relations in the population receiving immigrants by any arbitrary degree of prezygotic incompatibility. This corroborates Wallace's hypothesis and emphasizes the potential biological relevance of speciation by reinforcement (parapatric speciation) at single gene loci. (shrink)

Sexually active male haplochromine cichlid fishes possess pronounced yellow ovoid spots on the anal fm, which mimic eggs of the female and have therefore been called egg dummies (Wickler, 1962b).It is thought that divergence in egg dummy characteristics can considerably reduce gene flow and in this way may trigger off reproductive isolation. Two ways in which egg dummy divergence can develop are described. Both mechanisms may have been operating, at the same time and in the same area, in different species, (...) or possibly even in a single species. (shrink)