Mechanisms of Evolution

The meaning of niche and competitive ability have long been surrounded by controversy. The reason for this stems from the obscure relationship that exists between these terms. This extends from the views of Darwin through Eltonian tradition to current views in which the meaning of competitive ability is implicitly infused into the paradigm of niche. Distinct operational definitions for niche and competitive ability are therefore established with special reference to plants. It is proposed that potential niche refer explicitly to a (...) theoretical hyperspace of places where a species would leave descendents if all biotic interactions were precluded, and that competitive ability refer to the relative capacity to leave descendents in a particular place in the face of restrictions imposed by competitive interaction. This leads to a qualitative comprehensive theory for coexistence which may be extended to any type of biotic interaction. Niche and competitive ability are both determined by the biological attributes of a species and may be independently adjusted in a population by natural selection in contexts of competition. Species coexistence in nature may therefore be a consequence of alternative evolutionary mechanisms which may operate to various degrees in concert: (1) natural selection leading to niche differentiation; (2) an ongoing process of reciprocal selection (coevolution) which maintains an approximate balance in relative competitive abilities for contested resources. (shrink)

Recent debate on the nature of probabilities in evolutionary biology has focused largely on the propensity interpretation of fitness (PIF), which defines fitness in terms of a conception of probability known as “propensity”. However, proponents of this conception of fitness have misconceived the role of probability in the constitution of fitness. First, discussions of probability and fitness have almost always focused on organism effect probability, the probability that an organism and its environment cause effects. I argue that much of the (...) probability relevant to fitness must be organism circumstance probability, the probability that an organism encounters particular, detailed circumstances within an environment, circumstances which are not the organism’s effects. Second, I argue in favor of the view that organism effect propensities either don’t exist or are not part of the basis of fitness, because they usually have values close to 0 or 1. More generally, I try to show that it is possible to develop a clearer conception of the role of probability in biological processes than earlier discussions have allowed. (shrink)

One controversy about the existence of so called evolutionary forces such as natural selection and random genetic drift concerns the sense in which such “forces” can be said to interact. In this paper I explain how natural selection and random drift can interact. In particular, I show how population-level probabilities can be derived from individual-level probabilities, and explain the sense in which natural selection and drift are embodied in these population-level probabilities. I argue that whatever causal character the individual-level probabilities (...) have is then shared by the population-level probabilities, and that natural selection and random drift then have that same causal character. Moreover, natural selection and drift can then be viewed as two aspects of probability distributions over frequencies in populations of organisms. My characterization of population-level probabilities is largely neutral about what interpretation of probability is required, allowing my approach to support various positions on biological probabilities, including those which give biological probabilities one or another sort of causal character. ‡This paper has benefited from feedback on and discussions of this and earlier work. I want to thank André Ariew, Matt Barker, Lindley Darden, Patrick Forber, Nancy Hall, Mohan Matthen, Samir Okasha, Jeremy Pober, Robert Richardson, Alex Rosenberg, Eric Seidel, Denis Walsh, and Bill Wimsatt. †To contact the author, please write to: Department of Philosophy, University of Alabama at Birmingham, HB 414A, 900 13th Street South, Birmingham, AL 35294-1260; e-mail: mabrams@uab.edu. (shrink)

The target article skillfully evaluates data on mental disorders in relation to predictions from evolutionary genetic theories of neutral evolution, balancing selection, and polygenic mutation-selection balance, resulting in a negative outlook for the likelihood of success finding genes for mental disorders. Nevertheless, new conceptualizations, methods, and continued interactions across disciplines provide hope.

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)

Ostriches were filmed running at maximum speed, and forces on the feet were calculated. Measurements were made of the principal structures in the legs of an ostrich. Hence peak stresses in muscles, tendons and bones were calculated. They lay within the range of stresses calculated for strenuous activities of other vertebrates. The ostrich makes substantial savings of energy in running, by elastic storage in stretched tendons. Pachyornis was a flightless bird, much heavier than ostriches and with massively thick leg bones. (...) These bones are shorter than predicted for its estimated body mass, by extrapolation from allometric equations for flying birds. An attempt is made to calculate the stresses that acted in the leg bones in running, for all possible patterns of leg movement. The stresses were probably rather low, unless Pachyornis was capable of running fast. It is argued that the optimum factor of safety for moo leg bones may have been exceptionally high, as a consequence of the absence of predators. (shrink)

The concept of an ecological niche (econiche) has been used in a variety of ways, some of which are incompatible with a relational or functional interpretation of the term. This essay seeks to standardize usage by limiting the concept to functional relations between organisms and their surroundings, and to revise the concept to include epistemic relations. For most organisms, epistemics are a vital aspect of their functional relationships to their surroundings and, hence, a major determinant of their econiche. Rejecting the (...) traditional dualism of organism and environment, an econiche is defined as the reciprocal (dual) of a functionally specified class of organisms (FSTU). From this perspective, an econiche necessarily implies a certain type of organism, and a class of functionally similar organisms implies a special econiche.The econiche concept is also discussed in relation to other ecological terms that reflect the distributional patterns of organisms, such as habitat, and the concept of an empty niche is criticized. (shrink)

Many apparently complex mechanisms in biology, especially in embryology and molecular biology, can be explained easily by reasoning at the level of the “efficient cause” of the observed phenomenology: the mechanism can then be explained by a simple geometrical argument or a variational principle, leading to the solution of an optimization problem, for example, via the co-existence of a minimization and a maximization problem . Passing from a microscopic level to the macroscopic level often involves an averaging effect that gives (...) birth to a global functional feature . We will illustrate these general principles by building in four different domains of application “a minima” models and showing the main properties of their solutions: extraction of a minimal RNA structure functioning as the first “peptidic machine,” a kind of ancestral ribosome; study of a genetic regulatory network of Drosophila centred on Engrailed gene and expressing successively two genes inside a limit cycle; study of a genetic network regulating neural activity and proliferation in mammals; and study of a simple geometric model of epiboly in zebrafish. (shrink)

This paper examines the way Charles Darwin applied his domestic breeding analogy to the practical workings of species evolution: that application, it is argued, centered on Darwin's distinction between methodical and unconscious selection. Methodical selection, which entailed pairing particular individuals for mating purposes, represented conditions of strict geographic isolation, obviously useful for species multiplication (speciation). By contrast, unconscious selection represented an open landmass with a large breeding population. Yet Darwin held that this latter scenario, which often would include multiple ecological (...) subdistricts and thus partial isolation, was better suited for speciation than were isolated conditions. At the same time, many passages in Darwin's writings that apparently portrayed phyletic evolution exclusively (these including references to unconscious selection), actually applied to speciation as well, for phyletic change in a single district could constitute a local manifestation of a larger common-descent pattern. This generic use of "phyletic" change was reflected in Darwin's deployment of the unconscious selection analogy in his published writings as well as in his dispute with Moritz Wagner over the necessity of geographic isolation for speciation. We can thus understand Darwin's otherwise puzzling declaration in The Origin of Species that unconscious selection was 'more important' than the methodical approach. (shrink)

Long-term vegetation dynamics based on paleo-pollen data display transient behaviour, often alternating in phase between predominant determinism and predominant 'turbulence', when viewed as a trajectory in a multivariate phase space. Given this, the metaphor of vegetation dynamics as a 'flowing stream', first introduced by Cooper in his classic 1926 paper entitled "The fundamentals of vegetation change", is re-examined and revealed to be not only useful, but strikingly realistic. Vegetation dynamic theory is reviewed and classic theories are found to reflect reality (...) poorly. It is suggested that vegetation dynamics is a far from equilibrium system, and that the application of nonequilibrium thermodynamic theory is appropriate. (shrink)

Human knowledge is a phenomenon whose roots extend from the cultural, through the neural and the biological and finally all the way down into the Precambrian “primordial soup.” The present paper reports an attempt at understanding this Greater System of Knowledge (GSK) as a hierarchical nested set of selection processes acting concurrently on several different scales of time and space. To this end, a general selection theory extending mainly from the work of Hull and Campbell is introduced. The perhaps most (...) drastic change from previous similar theories is that replication is revealed as a composite function consisting of what is referred to as memory and synthesis. This move is argued to drastically improve the fit between theory and human-related knowledge systems. The introduced theory is then used to interpret the subsystems of the GSK and their interrelations. This is done to the end of demonstrating some of the new perspectives offered by this view. (shrink)

Volterra's (1926) equations for competition and predator-prey interactions are modified by introduction of root terms. A critical comparison with the original equations shows that the dynamic properties of the systems remain essentially alike, while the modification allows for explicit solution of the differential equations. Detailed solutions and numerical examples are given.

Historians of Biology have divided nineteenth century naturalists into two basic camps, Functionalists and Structuralists. This division is supposed to demarcate the alternative causal presuppositions working beneath research programs. If one is functionally oriented, then organic form will be contingent upon the causal powers of the environment. If structurally oriented, one argues for nonfunctional mechanisms (e.g., internal laws of growth) to account for organic form.Traditionally, Darwin has been grouped with the functionalists because natural selection (an adaptational mechanism) plays the prominent (...) role in shaping organic form. In this paper, I sketch the dichotomy of functionalism versus structuralism and then argue that Darwin cannot be characterized adequately with this dichotomy. I argue that Darwin can incorporate both causal stories because he makes two important modifications to the traditional metaphysical presuppositions. I then offer some brief reflections on the import of Darwin's causal pluralism for the Philosophy of Science. (shrink)

PDF version This talk explores three concepts of system in engineering: systems theory, systems approach, and systems engineering. They are exemplified in three dimensions of engineering: science, design, and management. Unifying the three system concepts is the idea of function: functional abstraction in theory, functional analysis in design, and functional requirements in management. Signifying what a system is for, function is a purposive notion absent in physical science, which aims to understand nature. It is prominent in engineering, which aims to (...) transform nature for serving the wants and needs of people. (shrink)

In recent years, some have claimed that a Darwinian perspective will revolutionize the study of human society and culture. This project is viewed with disdain and suspicion, on the other hand, by many practicing social scientists. This article seeks to clear the air in this heated debate by dissociating two claims that are too often assumed to be inseparable. The first is the ‘ontological’ claim that Darwinian principles apply, at some level of abstraction, to human society and culture. The second (...) is the more ‘pragmatic’ claim that this observation necessitates substantial changes in the practices of social scientists. Even if some version of the first claim is true, I argue – which I believe is quite likely – the second does not follow. This observation ought to chasten the most overzealous advocates of Darwinian social science, as well as softening the instinctive resistance of many social scientists and historians to the genuine insights enabled by a Darwinian approach. The conclusion discusses these insights, the most important of which is a methodological prescription for normative theory. (shrink)

This paper is concerned with adaptive learning and coordination processes. Implementing agent-based modeling techniques (Learning Classifier Systems, LCS), we focus on the twofold impact of cognitive and environmental complexity on learning and coordination. Within this framework, we introduce the notion of Adaptive Learning Agent with Rule-based Memory (ALARM), which is a particular class of Artificial Adaptive Agent (AAA, Holland and Miller 1991). We show that equilibrium is approached to a high degree, but never perfectly reached. We also demonstrate that memorization (...) and learning capacities depend upon the relative discordance between the cognitive complexity of agents' mental models and the degree of stability of the environment. (shrink)

This paper is about a general methodology for pattern transformation. Patterns are network representations of the relations among structures and functions within an organism. Transformation refers to any realistic or abstract transformation relevant to biology, e.g. ontogeny, evolution and phenotypic clines. The main aim of the paper is a methodology for analyzing the range of effects on a pattern due to perturbing one or more of its structures and/or functions (transformation morphology). Concepts relevant to such an analysis of pattern transformation (...) are reviewed and several new ones introduced: pattern unit; direct and indirect functional demands; compatibility and trade-off; integrating, adding and decoupling; functional effectiveness; spatial, profile and other architectonic constraints; domains of structure-function relations; goal and process adaptability; multiple pathways. The paper is written from the the perspective of architectonic morphology, viz. functional morphology focusing on the relation between anatomical coherence and the compatibility of functions. The advantages and disadvantages of inductive and deductive approaches are discussed. (shrink)

In addition to ensuring that appropriate standards of evidence are employed when attempting to identify adaptations, researchers should investigate all nonevolutionary factors that could potentially explain their results. Evolutionary analyses may be undermined by alternative, non-evolutionary explanations either because not all relevant information is included in an evolutionary analysis, or because inappropriate methods incapable of detecting an adaptation are employed.

Among the liveliest disputes in evolutionary biology today are disputes concerning the role of chance in evolution--more specifically, disputes concerning the relative evolutionary importance of natural selection vs. so-called "random drift". The following discussion is an attempt to sort out some of the broad issues involved in those disputes. In the first half of this paper, I try to explain the differences between evolution by natural selection and evolution by random drift. On some common construals of "natural selection", those two (...) modes of evolution are completely indistinguishable. Even on a proper construal of "natural selection", it is difficult to distinguish between the "improbable results of natural selection" and evolution by random drift. In the second half of this paper, I discuss the variety of positions taken by evolutionists with respect to the evolutionary importance of random drift vs. natural selection. I will then consider the variety of issues in question in terms of a conceptual distinction often used to describe the rise of probabilistic thinking in the sciences. I will argue, in particular, that what is going on here is not, as might appear at first sight, just another dispute about the desirability of "stochastic" vs. "deterministic" theories. Modern evolutionists do not argue so much about whether evolution is stochastic, but about how stochastic it is. (shrink)

During the 1950s and 60s, evolutionary biologists began to attribute a greater and greater role to natural selection, and correspondingly less and less a role to alternative evolutionary agents. Empirical grounds cited in support of the change in attitude consisted primarily of selectionist reinterpretations of evolutionary changes originally attributed to other evolutionary agents. In order to distinguish the respects in which the increased emphasis on natural selection was justified and unjustified, two distinctions are relied on. These are, first, the distinction (...) between pursuing an hypothesis and accepting it, and second, the distinction between what is reasonable/rational as far as individual scientists are concerned vs. what is reasonable/rational as far as the scientific community is concerned. It was rational for at least some individual scientists to pursue exclusively selectionist accounts on the basis of the selectionist successes in question, although it was not rational for any of them to accept the hypothesis of the all-importance of natural selection on those meager grounds. Moreover, although it was reasonable for at least some individual evolutionary biologists to invoke the selectionist successes in question in pursuit of further selectionist accounts, it was not reasonable for the entire community of evolutionary biologists to pursue exclusively selectionist accounts on those grounds. (shrink)

In many domains of biology, explanation takes the form of characterizing the mechanism responsible for a particular phenomenon in a specific biological system. How are such explanations generalized? One important strategy assumes conservation of mechanisms through evolutionary descent. But conservation is seldom complete. In the case discussed, the central mechanism for circadian rhythms in animals was first identified in Drosophila and then extended to mammals. Scientists' working assumption that the clock mechanisms would be conserved both yielded important generalizations and served (...) as a heuristic for discovery, especially when significant differences between the insect and mammalian mechanism were identified. †To contact the author, please write to: Department of Philosophy and Interdisciplinary Programs in Science Studies and Cognitive Science, 0119, University of California, San Diego, La Jolla, CA 92093‐0119; e‐mail: bill@mechanism.ucsd.edu. (shrink)

This paper concerns the relationship between the detectable and useful structure in an environment and the degree to which a population can adapt to that environment. We explore the hypothesis that adaptability will depend unimodally on environmental variety, and we measure this component of environmental structure using the information-theoretic uncertainty of detectable environmental conditions. We de ne adaptability as the degree to which a certain kind of population successfully adapts to a certain kind of environment, and we measure adaptability by (...) comparing a population's size to the size of a non-adapting, but otherwise comparable, population in the same environment. We study the relationship between adaptability and environmental structure in an evolving arti cial population of sensorimotor agents that live, reproduce, and die in a variety of environments. We nd that adaptability does not show a unimodal dependence on environmental variety alone, although there is justi cation for preserving our unimodal hypothesis if we consider other aspects of environmental structure. In particular, adaptability depends not just on how much structural information is detectable in the environment, but also on how unambiguous and valuable this information is, i.e., whether the information accurately signals a di erence that makes a di erence. How best to measure and integrate these other components of environmental structure remains unresolved. (shrink)

A number of recent discussions have argued that George Price's equationfor representing evolutionary change is a powerful and illuminatingtool, especially in the context of debates about multiple levels ofselection. Our paper dissects Price's equation in detail, and comparesit to another statistical tool: the calculation and comparison ofaverage fitnesses. The relations between Price's equation and equationsfor evolutionary change using average fitness are closer than issometimes supposed. The two approaches achieve a similar kind ofstatistical summary of one generation of change, and they (...) achieve thisvia a similar loss of information about the underlying fitnessstructure. (shrink)

In this philosophical paper, I discuss and illustrate the necessary three ingredients that together could allow a collective phenomenon to be labelled as “emergent.” First, the phenomenon, as usual, requires a group of natural objects entering in a non-linear relationship and potentially entailing the existence of various semantic descriptions depending on the human scale of observation. Second, this phenomenon has to be observed by a mechanical observer instead of a human one, which has the natural capacity for temporal or spatial (...) integration, or both. Finally, for this natural observer to detect and select the collective phenomenon, it needs to do so on account of the adaptive advantage this phenomenon is responsible for. The necessity for such a teleological characterization and the presence of natural selection drive us to defend, with many authors, the idea that emergent phenomena should belong only to biology. Following a brief philosophical plea, we present a simple and illustrative computer thought experiment in which a society of agents evolves a stigmergic collective behavior as an outcome of its greater adaptive value. The three ingredients are illustrated and discussed within this experimental context. Such an inclusion of the mechanical observer and the natural selection to which this phenomenon is submitted should underlie the necessary de-subjectivation that strengthens any scientific endeavor. I shall finally show why the short paths taken by ant colonies, the collective flying of birds and the maximum consumption of nutrients by a cellular metabolism are strongly emergent. (shrink)

This paper uses a 4 × 4 expansion of the Hawk–Dove Game to illustrate how sexual drift in a large genotype space can shift a population from one equilibrium in a smaller phenotype space to another. An equilibrium is only safe from being destabilized in this way when implemented by recessive alleles.

In a recent paper, Potochnik (Biol Philos 24(2):183–197, 2009) analyses some uses of optimality modelling in light of the anti-adaptationism criticism. She distinguishes two broad classes of such uses (weak and strong) on the basis of assumptions held by biologists about the role and the importance of natural selection. This is an interesting proposal that could help in the epistemological characterisation of some biological practices. However, Potochnik’s distinction also rests on the assumption that all optimality modelling represent the selection dynamic (...) involved in the system of phenomena being considered. Since this assumption does not hold for models belonging to optimal foraging theory (OFT)—one of behavioural ecology’s important modelling traditions—Potochnik’s proposal has to be critically reappraised. In this paper, we briefly discuss what is optimality modelling and what it means for a model to represent a dynamic of selection or of evolution. Then, we demonstrate that OFT modelling is unable to represent either past or contemporary selection dynamics. In order to make this point, we carefully delineate the theory’s rationale. This allows us to identify and analyse the assumptions on which the theory is built, and to circumscribe precisely the role that natural selection plays in it. Next, we show that the distinction of weak and strong uses of optimality modelling is seriously weakened when OFT modelling is taken into account. More precisely, the distinction is either irrelevant (if the assumption that selection dynamics are represented in all optimality modelling is held) or of a modest utility (if the assumption is dropped). However, we suggest that Potochnik’s original proposal could be saved, and that it even constitutes a tool to appraise the marks left in the literature by the evolution of optimality modelling practices in the last four decades, provided that it is made into a tripartite distinction. (shrink)

Genetic variability and diversity are the result of a mutation-selection balance that acts permanently within and between species. The presence of deleterious mutations is a necessary consequence of this process and thus the price paid by a species for its capacity for further evolution (Haldane 1937, Am Nat 71:337–349). Recent estimations of mutation rate in the human lineage has revived the debate as to whether the high number of deleterious mutations poses a severe problem for the future of mankind. Theoretical (...) considerations allow a scenario in which the survival of the human race is maintained by truncation selection of deleterious mutations that removes as many mutations as appear anew in every generation. In this case our genetic burden is carried by those individuals that suffer a genetic death resulting from random distribution of deleterious alleles. Nevertheless, one has to ask whether the mutation rate may set absolute limits on the complexity of a species. (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. Show Abstract.. (shrink)

It is striking that the concept of fitness although fundamental in evolutionary theory, still remains ambiguous. I argue here that time, although usually neglected, is an important parameter in regards to the concept of fitness. I will show some of the benefits of taking it seriously using the example of recent debates over evolutionary transitions in individuality. I start from Okasha's assertion that once an evolutionary transition in individuality is completed an ontologically new level of selection emerges from lower levels (...) of organization. I argue that Okasha's claim to have identified two ontologically distinct levels of selection is an artifact created by an undeserved comparison between the fitness of the collective level and the fitness of its constituents. Once fitness is assessed over the same period of time at the two levels of organization it becomes clear that only one, unique process of selection is acting upon both levels. (shrink)

It is desirable that the antecedents of existing, highly specialised, evolutionary mechanisms in animals be sought. The study of the lower Metazoa and especially of their simpler reproductive processes suggests that asexual reproduction is the primitive evolutionary mechanism from which the more advanced sexual mechanisms have evolved. A study of the metagenetic cycles of Coelenterata and Platyhelminthes seems to throw much light upon their prophylogeny and indicates that: Such cycles seem to provide the closest possible recapitulatory parallelism between phylogeny and (...) ontogeny. The Hydrozoa are ancestral to the other classes of Coelenterata. The polypoid adult is more primitive than the medusoid adult. The sporocysts, rediae and scolices represent the more primitive types of adults in their respective ontogenies and phylogenies.On avance la théorie qu'il y a eu une évolution des mécanismes évolutionnaires depuis les stades primitifs jusqu'aux stades avancés. D'après cette théorie les premières étapes dans l'évolution des Métazoaires inférieurs se sont effectuées par la reproduction asexuelle avant que les mecanismes sexuels très spécialisés se soient manifestés.Des preuves à l'appui de cette théorie découlent: de la rencontre actuelle d'une reproduction asexuelle chez des animaux, avec l'indication que sa simplicité est, dans la plupart des cas, originelle, et des cycles d'évolution des Coelentérés et Platyhelminthes qui sont métagénésiques. Leurs cycles peuvent s'interpréter comme partant de stades reproductifs asexuels pour évoluer vers des formes se reproduisant sexuellement.On croit que les organismes ne pouvant se reproduire que sexuellement sont plus avancés que ceux qui peuvent se reproduire asexuellement, ou à la fois sexuellement et asexuellement.Cette théorie a d'importantes implications pour l'étude de la métagenèse, de la récapitulation et de la phylogénie chez les Métazoaires inférieurs; elle exemplifie, dans l'étude de ces phénomènes, la nouvelle orientation qu'on a appelée Prophylogénie.In dieser Arbeit wird eine Theorie entwickelt, die besagt, dass eine Fortentwicklung der Evolutionsmechanismen von primitiven zu fortgeschrittenen Stufen besteht. Dieser Theorie nach haben sich die niedrigeren Metazoen ursprünglich nur ungeschlechtlich entwickelt und fortgepflanzt. Erst später haben sich die höchst spezialisierten geschlechtlichen Mechanismen entwickelt.Belege für diese Theorie sind: Noch heute kommt die geschlechtslose Fortpflanzung in Tieren vor, was dafür spricht, dass ihre Einfachheit in den meisten Fällen ursprünglich ist. Die Lebenskreisläufe der Metagenetischen Coelenteraten und Platyhelminthen lassen sich interpretieren als bestehend aus ursprünglich ungeschlechtlichen Fortpflanzungsstufen, die jedoch später in Formen mit geschlechtlicher Fortpflanzung übergehen.Es wird behauptet, dass Organismen mit nur geschlechtlicher Fortpflanzung weiter fortgeschritten sind als solche mit nur ungeschlechtlicher oder mit sowohl ungeschlechtlicher als auch geschlechtlicher Fortpflanzung.Diese Theorie ist wichtig für das Studium der Metagenese, Rekapitulation und Phylogenie in den niedrigen Metazoen und veranschaulicht die Prophylogenie, d.h. die neue Methode im Studium dieser Erscheinungen. (shrink)

Darwin's theory of evolution by natural selection provided the first, and only, causal-mechanistic account of the existence of adaptations in nature. As such, it provided the first, and only, scientific alternative to the “argument from design”. That alone would account for its philosophical significance. But the theory also raises other philosophical questions not encountered in the study of the theories of physics. Unfortunately the concept of natural selection is intimately intertwined with the other basic concepts of evolutionary theory—such as the (...) concepts of fitness and adaptation —that are themselves philosophically controversial. Fortunately we can make considerable headway in getting clear on natural selection without solving all of those outstanding problems. (shrink)

Drift is to evolution as inertia is to Newtonian mechanics. Both are the "natural" or default states of the systems to which they apply. Both are governed by zero-force laws. The zero-force law in biology is stated here for the first time.

Millstein [Bio. Philos. 17 (2002) 33] correctly identies a serious problem with the view that natural selection and random drift are not conceptually distinct. She offers a solution to this problem purely in terms of differences between the processes of selection and drift. I show that this solution does not work, that it leaves the vast majority of real biological cases uncategorized. However, I do think there is a solution to the problem she raises, and I offer it here. My (...) solution depends on solving the biological analogue of the reference class problem in probability theory and on the reality of individual fitnesses. (shrink)

Integrating concepts of maintenance and of origins is essential to explaining biological diversity. The unified theory of evolution attempts to find a common theme linking production rules inherent in biological systems, explaining the origin of biological order as a manifestation of the flow of energy and the flow of information on various spatial and temporal scales, with the recognition that natural selection is an evolutionarily relevant process. Biological systems persist in space and time by transfor ming energy from one state (...) to another in a manner that generates structures which allows the system to continue to persist. Two classes of energetic transformations allow this; heat-generating transformations, resulting in a net loss of energy from the system, and conservative transformations, changing unusable energy into states that can be stored and used subsequently. All conservative transformations in biological systems are coupled with heat-generating transformations; hence, inherent biological production, or genealogical proesses, is positively entropic. There is a self-organizing phenomenology common to genealogical phenomena, which imparts an arrow of time to biological systems. Natural selection, which by itself is time-reversible, contributes to the organization of the self-organized genealogical trajectories. The interplay of genealogical (diversity-promoting) and selective (diversity-limiting) processes produces biological order to which the primary contribution is genealogical history. Dynamic changes occuring on times scales shorter than speciation rates are microevolutionary; those occuring on time scales longer than speciation rates are macroevolutionary. Macroevolutionary processes are neither redicible to, nor autonomous from, microevolutionary processes. (shrink)

Constructive Neutral Evolution is an evolutionary mechanism that can explain much molecular inter-dependence and organismal complexity without assuming positive selection favoring such dependency or complexity, either directly or as a byproduct of adaptation. It differs from but complements other non-selective explanations for complexity, such as genetic drift and the Zero Force Evolutionary Law, by being ratchet-like in character. With CNE, purifying selection maintains dependencies or complexities that were neutrally evolved. Preliminary treatments use it to explain specific genetic and molecular structures (...) or processes, such as retained gene duplications, the spliceosome, and RNA editing. Here we aim to expand the scope of such explanation beyond the molecular level, integrating CNE with Multi-Level Selection theory, and arguing that several popular higher-level selection scenarios are in fact instances of CNE. Suitably contextualized, CNE occurs at any level in the biological hierarchy at which natural selection as normally construed occurs. As examples, we focus on modularity in protein–protein interaction networks or “interactomes,” the origin of eukaryotic cells and the evolution of co-dependence in microbial communities—a variant of the “Black Queen Hypothesis” which we call the “Gray Queen Hypothesis”. (shrink)