The meaning of the word homology has changed. From being a comparative concept in pre-Darwinian times, it became a historical concept, strictly signifying a common evolutionary origin for either anatomical structures or genes. This historical understanding of homology is not useful in classification; therefore I propose a return to its pre-Darwinian meaning.
This article reviews the recent reissuing of Richard Owen’s On the Nature of Limbs and its three novel, introductory essays. These essays make Owen’s 1849 text very accessible by discussing the historical context of his work and explaining how Owen’s ideas relate to his larger intellectual framework. In addition to the ways in which the essays point to Owen’s relevance for contemporary biology, I discuss how Owen’s unity of type theory and his homology claims about ﬁns and limbs compare with (...) modern views. While the phenomena studied by Owen are nowadays of major interest to evolutionary developmental biology, research in evo-devo has largely shifted from homology (which was Owen’s concern) towards evolutionary novelty, e.g., accounting for ﬁns as a novelty. Still, I argue that questions about homology are important and raise challenges even for explanations of novelty. (shrink)
Taxa and homologues can in our view be construed both as kinds and as individuals. However, the conceptualization of taxa as natural kinds in the sense of homeostatic property cluster kinds has been criticized by some systematists, as it seems that even such kinds cannot evolve due to their being homeostatic. We reply by arguing that the treatment of transformational and taxic homologies, respectively, as dynamic and static aspects of the same homeostatic property cluster kind represents a good perspective for (...) supporting the conceptualization of taxa as kinds. The focus on a phenomenon of homology based on causal processes (e.g., connectivity, activity-function, genetics, inheritance, and modularity) and implying relationship with modification yields a notion of natural kinds conforming to the phylogenetic-evolutionary framework. Nevertheless, homeostatic property cluster kinds in taxonomic and evolutionary practice must be rooted in the primacy of epistemological classification (homology as observational properties) over metaphysical generalization (series of transformation and common ancestry as unobservational processes). The perspective of individuating characters exclusively by historical-transformational independence instead of their developmental, structural, and functional independence fails to yield a sufficient practical interplay between theory and observation. Purely ontological and ostensional perspectives in evolution and phylogeny (e.g., an ideographic character concept and PhyloCode’s ‘individualism’ of clades) may be pragmatically contested in the case of urgent issues in biodiversity research, conservation, and systematics. (shrink)
While it is generally agreed that the concept of homology refers to individuated traits that have been inherited from common ancestry, we still lack an adequate account of trait individuation or inheritance. Here I propose that we utilize a counterfactual criterion of causation to link each trait with a developmental-causal (DC) gene. A DC gene is made up of the genetic information (which might or might not be physically contiguous in the genome) that is needed for the production of the (...) organismic attributes that comprise the trait. I argue that individuated traits—phenes—correspond to organismic features that are caused by DC genes. Using such an approach, we can define a DC map, which shows the relations between each pair of phenes and provides a succinct summary of genotype-phenotype relationships and phenotypic complexity. Phenes in parents and offspring are judged to be homologous if their DC genes are composed of orthologous genetic factors. When comparing more distantly related organisms, traits are homologous when linked by a chain of parent-offspring homologs along the path of ancestry that links the two organisms. There are three possible ways to deal with the potential for multiple equivalent DC genes: maximal, minimal, and consensus homology. Whereas maximal homology has limited utility, the other two approaches have value and can help to guide research at the intersection of evolution and development. (shrink)
The theory of concepts advanced in the present discussion aims at accounting for a) how a concept makes successful practice possible, and b) how a scientific concept can be subject to rational change in the course of history. To this end, I suggest that each scientific concept consists of three components of content: 1) the concept.
The paper discusses reference determination from the point of view of conceptual change in science. The first part of the discussion uses the homology concept, a natural kind term from biology, as an example. It is argued that the causal theory of reference gives an incomplete account of reference determination even in the case of natural kind terms. Moreover, even if descriptions of the referent are taken into account, this does not yield a satisfactory account of reference in the case (...) of the homology concept. I suggest that in addition to the factors that standard theories of reference invoke the scientific use of concepts and the epistemic interests pursued with concepts are important factors in determining the reference of scientific concepts. In the second part, I argue for a moderate holism about reference determination according to which the set of conditions that determine the reference of a concept is relatively open and different conditions may be reference fixing depending on the context in which this concept is used. It is also suggested that which features are reference determining in a particular case may depend on the philosophical interests that underlie reference ascription and the study of conceptual change. (shrink)
The present paper gives a philosophical analysis of the conceptual variation in the homology concept. It is argued that different homology concepts are used in evolutionary and comparative biology, in evolutionary developmental biology, and in molecular biology. The study uses conceptual role semantics, focusing on the inferences and explanations supported by concepts, as a heuristic tool to explain conceptual change. The differences between homology concepts are due to the fact that these concepts play different theoretical roles for different biological fields. (...) The specific theoretical needs and explanatory interests of different research approaches lead to different homology concepts. (shrink)
Despite the traditional focus on metaphysical issues in discussions of natural kinds in biology, epistemological considerations are at least as important. By revisiting the debate as to whether taxa are kinds or individuals, I argue that both accounts are metaphysically compatible, but that one or the other approach can be pragmatically preferable depending on the epistemic context. Recent objections against construing species as homeostatic property cluster kinds are also addressed. The second part of the paper broadens the perspective by considering (...) homologues as another example of natural kinds, comparing them with analogues as functionally defined kinds. Given that there are various types of natural kinds, I discuss the different theoretical purposes served by diverse kind concepts, suggesting that there is no clear-cut distinction between natural kinds and other kinds, such as functional kinds. Rather than attempting to offer a unique metaphysical account of ‘natural’ kind, a more fruitful approach consists in the epistemological study of how different natural kind concepts are employed in scientific reasoning. (shrink)
This article reviews the recent reissuing of Richard Owen’s On the Nature of Limbs and its three novel, introductory essays. These essays make Owen’s 1849 text very accessible by discussing the historical context of his work and explaining how Owen’s ideas relate to his larger intellectual framework. In addition to the ways in which the essays point to Owen’s relevance for contemporary biology, I discuss how Owen’s unity of type theory and his homology claims about fins and limbs compare with (...) modern views. While the phenomena studied by Owen are nowadays of major interest to evolutionary developmental biology, research in evo-devo has largely shifted from homology (which was Owen’s concern) towards evolutionary novelty, e.g., accounting for fins as a novelty. Still, I argue that questions about homology are important and raise challenges even for explanations of novelty. (shrink)
This article reviews the recent reissuing of Richard Owen’s On the Nature of Limbs and its three novel, introductory essays. These essays make Owen’s 1849 text very accessible by discussing the historical context of his work and explaining how Owen’s ideas relate to his larger intellectual framework. In addition to the ways in which the essays point to Owen’s relevance for contemporary biology, I discuss how Owen’s unity of type theory and his homology claims about fins and limbs compare with (...) modern views. While the phenomena studied by Owen are nowadays of major interest to evolutionary developmental biology, research in evo devo has largely shifted from homology (which was Owen’s concern) towards evolutionary novelty, e.g., accounting for fins as a novelty. Still, I argue that questions about homology are important and raise challenges even for explanations of novelty. (shrink)
By linking the concepts of homology and morphological organization to evolvability, this paper attempts to (1) bridge the gap between developmental and phylogenetic approaches to homology and to (2) show that developmental constraints and natural selection are compatible and in fact complementary. I conceive of a homologue as a unit of morphological evolvability, i.e., as a part of an organism that can exhibit heritable phenotypic variation independently of the organism’s other homologues. An account of homology therefore consists in explaining how (...) an organism’s developmental constitution results in different homologues/characters as units that can evolve independently of each other. The explanans of an account of homology is developmental, yet the very explanandum is an evolutionary phenomenon: evolvability in a character-by-character fashion, which manifests itself in phylogenetic patterns as recognized by phylogenetic approaches to homology. While developmental constraints and selection have often been viewed as antagonistic forces, I argue that both are complementary as they concern different parts of the evolutionary process. Developmental constraints, conceived of as the presence of the same set of homologues across phenotypic change, pertain to how heritable variation can be generated in the first place (evolvability), while natural selection operates subsequently on the produced variation. (shrink)
The evolutionary embryologist Gavin Rylands de Beer can be viewed as one of the forerunners of modern evolutionary developmental biology in that he posed crucial questions and proposed relevant answers about the causal relationship between ontogeny and phylogeny. In his developmental approach to the phylogenetic phenomenon of homology, he emphasized that homology of morphological structures is to be identified neither with the sameness of the underlying developmental processes nor with the homology of the genes that are in involved in the (...) development of the structures. De Beer’s work on developmental evolution focused on the notion of heterochrony, arguing that paedomorphosis increases morphological evolvability and is thereby an important mode of evolution that accounts for the origin of many taxa, including higher taxa. (shrink)
This paper uses an example from biology, the homology concept, to argue that current versions of the causal theory of reference give an incomplete account of reference determination. It is suggested that in addition to samples and stereotypical properties, the scientific use of concepts and the epistemic interests pursued with concepts are important factors in determining the reference of natural kind terms.
The present paper analyzes the use and understanding of the homology concept across different biological disciplines. It is argued that in its history, the homology concept underwent a sort of adaptive radiation. Once it migrated from comparative anatomy into new biological fields, the homology concept changed in accordance with the theoretical aims and interests of these disciplines. The paper gives a case study of the theoretical role that homology plays in comparative and evolutionary biology, in molecular biology, and in evolutionary (...) developmental biology. It is shown that the concept or variant of homology preferred by a particular biological field is used to bring about items of biological knowledge that are characteristic for this field. A particular branch of biology uses its homology concept to pursue its specific theoretical goals. (shrink)
Homology is a natural kind term and a precise account of what homologyis has to come out of theories about the role of homologues in evolution anddevelopment. Definitions of homology are discussed with respect to the questionas to whether they are able to give a non-circular account of thecorrespondenceor sameness referred to by homology. It is argued that standard accounts tiehomology to operational criteria or specific research projects, but are not yetable to offer a concept of homology that does not (...) presuppose a version ofhomology or a comparable notion of sameness. This is the case for phylogeneticdefinitions that trace structures back to the common ancestor as well as fordevelopmental approaches such as Wagner's biological homology concept. Incontrast, molecular homology is able to offer a definition of homology in genesand proteins that explicates homology by reference to more basic notions.Molecular correspondence originates by means of specific features of causalprocesses. It is speculated that further understanding of morphogenesis mightenable biologists to give a theoretically deeper definition of homology alongsimilar lines: an account which makes reference to the concrete mechanisms thatoperate in organisms. (shrink)
This paper examines the middle ear of fossil living animals in terms of the homologies which have been drawn between its parts in different vertebrate groups. Seven homologies are considered: 1, the middle ear cavity/spiracular pouch; 2, the stapes/hyomandibula; 3, the stapedial/hyomandibular processes; 4 the tympanic membrane; 5, the otic notch; 6, the fenestra ovalis; 7, and the stapedial/hyomandibular foramen. The reasons leading to assessments of homology are reviewed. Homologies 1 and 2, based largely on embryological evidence, are fairly robust, (...) though there are arguments about the details. Homologies 3, 4 and 5 stem from ideas about early tetrapod evolution, and were influenced by contingent factors including the order and time of discovery of early fossil taxa, and perceptions of their phylogeny which resulted from this. They were also influenced by ideas of the evolution of terrestriality among tetrapods. Most of the conceptions have been overturned in recent years by new fossil discoveries and new ways of looking at old data. Homology 6 has been little considered. One possible hypothesis, placed in a strictly archetypal theoretical framework has been ignored but deserves consideration on other grounds. Homology 7 depends on how tetrapods are characterised, not a question which has posed difficulties until recently, but which is likely to with the discovery of intermediate fossil forms. (shrink)
In the last 10 years, several authors including Griffiths and Matthen have employed classificatory principles from biology to argue for a radical revision in the way that we individuate psychological traits. Arguing that the fundamental basis for classification of traits in biology is that of ‘homology’ (similarity due to common descent) rather than ‘analogy’, or ‘shared function’, and that psychological traits are a special case of biological traits, they maintain that psychological categories should be individuated primarily by relations of homology (...) rather than in terms of shared function. This poses a direct challenge to the dominant philosophical view of how to define psychological categories, viz., ‘functionalism’. Although the implications of this position extend to all psychological traits, the debate has centered around ‘emotion’ as an example of a psychological category ripe for reinterpretation within this new framework of classification. I address arguments by Griffiths that emotions should be divided into at least two distinct classes, basic emotions and higher cognitive emotions, and that these two classes require radically different theories to explain them. Griffiths argues that while basic emotions in humans are homologous to the corresponding states in other animals, higher cognitive emotions are dependent on mental capacities unique to humans, and are therefore not homologous to basic emotions. Using the example of shame, I argue that (a) many emotions that are commonly classified as being higher cognitive emotions actually correspond to certain basic emotions, and that (b) the “higher cognitive forms” of these emotions are best seen as being homologous to their basic forms. (shrink)
Current issues concerning the nature of ancestry and homology are discussed with reference to the evolutionary origin of the tetrapod limb. Homologies are argued to be complex conjectural inferences dependant upon a pre-existing phylogenetic analysisand a theoretical model of the evolutionary development of ontogenetic information. Ancestral conditions are inferred primarily from character (synapomorphy/homology) distributions within phylogeny, because of the deficiencies of palaeontological data. Recent analyses of tetrapod limb ontogeny, and the diverse, earliest morphologies known from the fossil record, are inconsistent (...) with typological concepts such as fixed ancestral patterns or bauplans, emphasising the incompatibility of these with evolutionary continuity. The evolutionary origin of the tetrapod limb is also examined in the light of its recent discussion in developmental genetics. While this field promises to reveal more of the fundamental ontogenetic content of homology (identity), at present it is concerned mostly with the abstraction of a new set of types, rather than investigating diversity and change. (shrink)
The comparative method grants epistemic access to the biological past. Comparing lineages provides empirical traction on both hypotheses about particular lineages and models of trait evolution. Understanding this evidential role is important. Although philosophers have recently turned their attention to relations of descent (homology), little work exists exploring the status of evidence from convergences (analogy). I argue that, where they exist, convergences play a central role in the confirmation of adaptive hypotheses. I focus on ‘analogous inferences’ (inferences that take a (...) trait–environment dyad from one lineage and project it to another), show how such inferences ought to be analysed and suggest three methods for strengthening their evidential weight. 1 Introduction2 Analogous Inferences2.1 Adaptive explanations and analogies2.2 Analogous inferences2.3 Scope, grain, and specificity3 Parallel Modelling, Integrated Explanations, and Convergent Modelling3.1 Parallel modelling3.2 Integrated explanations3.1 Convergent modelling4 Conclusion. (shrink)
I develop an account of homology and homoplasy drawing on their use in biological inference and explanation. Biologists call on homology and homoplasy to infer character states, support adaptationist explanations, identify evolutionary novelties and hypothesize phylogenetic relationships. In these contexts, the concepts must be understood phylogenetically and kept separate: as they play divergent roles, overlap between the two ought to be avoided. I use these considerations to criticize an otherwise attractive view defended by Gould, Hall, and Ramsey & Peterson. By (...) this view, homology and homoplasy can only be delineated qua some level of description, and some homoplasies (parallelisms) are counted as homologous. I develop an account which retains the first, but rejects the second, aspect of that view. I then characterize parallelisms and convergences in terms of their causal role. By the Strict Continuity account, homology and homoplasy are defined phylogenetically and without overlaps, meeting my restriction. Convergence and parallelisms are defined as two types of homoplasy: convergent homoplasies are largely constrained by external factors, while parallelisms are due to internal constraints. (shrink)
The importance of homology in biology is widely acknowledged. Wake (1994: 284) writes that “[h]omology is the central concept for all of biology.” Paterson (1987: 18) observes that “all useful comparisons in biology depend on the relation of homology.” Whenever we ask if two characters are the same character we are asking if they are homologous, regardless of whether those characters are genetic, morphological, anatomical, or behavioral. Yet like many central concepts in biology, our understanding of homology is plagued by (...) unresolved questions. For example, how should we define ‘homology’? There is no agreed upon definition in the literature. Or, how do we explain the fact that two homologous characters can be caused by non-homologous developmental factors (Hall 2007)? Or more fundamentally, what causes new homologues (Wagner 2001)? Then there are questions about the role of homologies in evolution. Homologues are quasi-independent, heritable units that selection acts on; they are units of evolvability (Laubichler 2000; Brigandt 2007). The idea of homologues as units of evolvability cries out for analysis. These are all pressing questions, but this paper will focus on just two of them. One is the possibility of a unified theoretical account of homology. The other is how homologues at one hierarchical level are caused by non-homologues at a lower level. As we shall see, recent work offers an emerging approach to homology that integrates phylogeny and development (Laubichler 2000). Such an approach provides the basis for a unified theoretical account of homology, and it sheds light on the hierarchical nature of homology. (shrink)
This paper explores an important type of biological explanation called ‘homology thinking.’ Homology thinking explains the properties of a homologue by citing the history of a homologue. Homology thinking is significant in several ways. First, it offers more detailed explanations of biological phenomena than corresponding analogy explanations. Second, it provides an important explanation of character similarity and difference. Third, homology thinking offers a promising account of multiple realizability in biology.
Most cognitive scientists nowadays tend to think that at least some of the mind’s capacities are the product of biological evolution, yet important conceptual problems remain for all of them in order to be able to speak coherently of mental or cognitive systems as having evolved naturally. Two of these important problems concern the articulation of adequate, interesting and empirically useful concepts of homology and variation as applied to cognitive systems. However, systems in cognitive science are usually understood as functional (...) systems of some sort. Thus, talking about functional systems’ being homologous requires one’s having a solid, adequate and empirically articulated concept of functional homology—and the same is true of functional variation. Here I construct an original concept of functional homology that, in my view, adequately systematizes a number of the actual uses of the word ‘functional homology’ in a variety of biological disciplines and in ethology. I also propose a number of criteria for the empirical application of the concept that are analogous to the criteria that are actually used in comparative biology, ethology, and (possibly) molecular developmental genetics. Then I construct a concept of functional variation on the basis of this concept of homology. (shrink)
Homology continues to be a concept of central importance in the study of phylogenetic relations, but its relation to ontogenetic processes remains problematical. A definition of homology in terms of equivalent morphogenetic processes is defined and applied to the comparative study of tetrapod limbs. This allows for a consistent treatment of relations of similarity and difference of appendage structure in vertebrates, and the distinction between fishes fins and tetrapod limbs in terms of the concept of equivalence is described. The role (...) of genes can also be clarified in this context, in particular the influence of the Hox 4 complex in determining digit character and the homeotic transformations that arise from changes in their expression patterns. It is argued that these observations are not compatible with the notion of homology between individual digits (I, II, III, etc.) across the tetrapods, and that homology cannot be consistently identified with gene action. The relations between homology and the properties of the morphogenetic limb field are discussed. (shrink)
Philosophical discussions of biological classification have failed to recognise the central role of homology in the classification of biological parts and processes. One reason for this is a misunderstanding of the relationship between judgments of homology and the core explanatory theories of biology. The textbook characterisation of homology as identity by descent is commonly regarded as a definition. I suggest instead that it is one of several attempts to explain the phenomena of homology. Twenty years ago the ‘new experimentalist’ movement (...) in philosophy of science drew attention to the fact that many experimental phenomena have a ‘life of their own’: the conviction that they are real is not dependent on the theories used to characterise and explain them. I suggest that something similar can be true of descriptive phenomena, and that many homologies are phenomena of this kind. As a result the descriptive biology of form and function has a life of its own—a degree of epistemological independence from the theories that explain form and function. I also suggest that the two major ‘homology concepts’ in contemporary biology, usually seen as two competing definitions, are in reality complementary elements of the biological explanation of homology. (shrink)
Many philosophers believe that 1) most uses of functional language in biology make implicit reference to natural selection and 2) the fundamental way in which biologists identify parts and processes in organisms is by their selected function(s). Both these claims are mistaken. Much functional language in biology refers to actual causal roles, and if this were not so, biology would be impossible. The extensive biological literature on the ‘character concept’ focuses on another principle of biological identity, namely homology. I outline (...) some of this work and use it to refute philosophical arguments for the importance and ubiquity of classification by adaptive function. (shrink)
I defend the view that many biological categories are defined by homology against a series of arguments designed to show that all biological categories are defined, at least in part, by selected function. I show that categories of homology are `abnormality inclusive'—something often alleged to be unique to selected function categories. I show that classifications by selected function are logically dependent on classifications by homology, but not vice-versa. Finally, I reject the view that biologists must use considerations of selected function (...) to abstract away from variation and pathology to form a canonical description of a class of biological systems. (shrink)
Aboitiz and colleagues propose that the tectorotundal pathway of birds and reptiles is homologous not to the mammalian colliculopulvinar system but to the posterior complex/intralaminar nuclei. However, as outlined below, a large amount of strong evidence points to a homology of the tectorotundal and the colliculopulvinar system. This makes it likely that DVR and isocortex might be in part homologous.
American biologists in the late nineteenth century pioneered the descriptive-comparative study of all cell divisions from zygote to gastrulation -- the cell lineage. Data from cell lineages were crucial to evolutionary and developmental questions of the day. One of the main questions was the ultimate causation of developmental patterns -- historical or mechanical. E. B. Wilson's groundbreaking lineage work on the polychaete worm Nereis in 1892 set the stage for (1) an attack on Haeckel's phylogenetic-historical notion of recapitulation and (2) (...) support for mechanistic explanations of cleavage patterns. As more lineage work -- especially Lillie's work on "Unio" and Conklin's on "Crepidula" -- became available in the mid-late 1890s, mechanism was tempered with more evolutionary, homology-based views. However, as I show by focusing on three major issues -- homology, body plans and life history -- these views were primarily based on the precocious segregation and prospective significance -- what the cell became not what it was. Even on issues like adaptation, most lineagists argued teleologically from the adult backward. Most cell lineage workers, by 1900, were to varying degrees mechanist/experimentalist and recapitulationist simultaneously. The exception was E. G. Conklin, whose views were more akin to a Darwinian evolutionist than either mechanist or recapitulationist. Lineage work eventually declined and by 1907 published accounts of new lineages had basically stopped. I argue that established workers and younger researchers stopped wanting to take on cell lineage projects because the general patterns were the same for all the spiralians while the specifics showed too much variation. It was hard to theoretically encompass or analyze the minutiae of variation in a recapitulationist or mechanist framework. The only established worker who continued to do comparative lineage studies was E. G. Conklin, perhaps because the variation could best be accommodated by Darwinian evolution. (shrink)
The Common Anatomy Reference Ontology (CARO) is being developed to facilitate interoperability between existing anatomy ontologies for different species, and will provide a template for building new anatomy ontologies. CARO has a structural axis of classification based on the top-level nodes of the Foundational Model of Anatomy. CARO will complement the developmental process sub-ontology of the GO Biological Process ontology, using it to ensure the coherent treatment of developmental stages, and to provide a common framework for the model organism communities (...) to classify developmental structures. Definitions for the types and relationships are being generated by a consortium of investigators from diverse backgrounds to ensure applicability to all organisms. CARO will support the coordination of cross-species ontologies at all levels of anatomical granularity by cross-referencing types within the cell type ontology (CL) and the Gene Ontology (GO) Cellular Component ontology. A complete cross-species CARO could be utilized in other ontologies for cross-product generation. (shrink)
Stephen Rose's formulation of evolutionary theory is too scattered and impressionistic to serve as a genuine alternative to ultra- Darwinism. In addition, he has muddied a distinction that is crucial to our understanding of evolutionary phenomenona – the distinction between homologies and homoplasies.
Homology concepts are fundamental to the study of biological similarity. Monistic attempts to articulate an overarching homology concept, applicable to all areas of biology, have yet to succeed. Biology is fundamentally pluralistic, and multiple homology concepts, applicable at different levels of the biological hierarchy, allow a more thorough investigation of the nature of biological similarity. Articulating the definition and causes associated with any homology concept ensures that the pluralistic approach advocated here is neither relativistic nor defeatist, but generative of fruitful (...) biological research. (shrink)
The study of similarity is fundamental to biological inquiry. Many homology concepts have been formulated that function successfully to explain similarity in their native domains, but fail to provide an overarching account applicable to variably interconnected and independent areas of biological research despite the monistic standpoint from which they originate. The use of multiple, explicitly articulated homology concepts, applicable at different levels of the biological hierarchy, allows a more thorough investigation of the nature of biological similarity. Responsible epistemological pluralism as (...) advocated herein is generative of fruitful and innovative biological research, and is appropriate given the metaphysical pluralism that underpins all of biology. (shrink)
Homology has been one of, if not the most, fecund concepts which has been used towards the understanding of the genomes of the model organisms. The evidence for this claim can be supported best with an examination of current research in comparative genomics. In comparative genomics, the information of genes or segments of the genome, and their location and sequence, are used to search for genes similar to them, known as 'homologues'. Homologues can be either within that same organism (paralogues), (...) or among different species (orthologues). The importance in finding homologous genes within organisms or across species is that these similarities indicate the possibility of ascribing functions, mechanisms or structures which are required by a variety of species which present the same homology. The interest in structures and functions of genes and proteins common to multiple species is one of the main foci of comparative genomics. Because of this, research into the conservation of genes has been the basis of comparison with regards to homologous genes among diverse organisms. Different causal processes are involved in genetic pathways and mechanisms. Explanations of these depend upon which pathway, structure or mechanism is picked out. Each process has a different causal network to which different explanations refer. What comparative genomics explains are the different causal mechanisms which occur in processes such as differentiation, protein synthesis, and gene regulation. How these processes interact within the organism can only be understood when compared with organisms which possess homologous genes, gene sequences, similar developmental mechanisms, or those whose mechanisms for gene regulation are similar. Explanations which result from comparative genomics contribute to a more comprehensive understanding of both the complex structures and the diverse functions within the genomes of different organisms. There are two related problems which have plagued attempts to define the concept of homology. The first problem arises in clarifying what kind of similarity is involved in a homological comparison. A second problem occurs if more than one concept of homology is needed to pick out the kinds of similarity in different contexts of homological comparison. Homology is usually understood as picking out what counts as 'the same' between two or more organisms. Many of the attempts which have been made to define the concept of homology focus on which criteria are used to restrict the kinds of similarity which exist between two or more organisms or parts being compared. These are criteria which can be used reliably to infer shared ancestry. However, there have been many different attempts to define similarity which have produced a profusion of homology concepts. This profusion has led both to the conflation of what counts as 'the same' in different contexts and has also muddled the relations of comparison which various concepts use to identify homologues. (shrink)
Homology is among the most important comparative concepts in biology. Today, the evolutionary reinterpretation of homology is usually conceived of as the most important event in the development of the concept. This paradigmatic turning point, however important for the historical explanation of life, is not of crucial importance for the development of the concept of homology itself. In the broadest sense, homology can be understood as sameness in reference to the universal guarantor so that in this sense the different concepts (...) of homology show a certain kind of “metahomology”. This holds in the old morphological conception, as well as in the evolutionary usage of homology. Depending on what is (or was) taken as a guarantor, different types of homology may be distinguished (as idealistic, historical, developmental etc.). This study represents a historical overview of the development of the homology concept followed by some clues on how to navigate the pluralistic terminology of modern approaches to homology. (shrink)
The ‘byproduct account’ of female orgasm, a subject of renewed debate since Lloyd (The case of the female orgasm, Harvard University Press, Cambridge, 2005), is universally attributed to Symons (The evolution of human sexuality, Oxford University Press, Oxford, 1979). While this is correct to the extent that he linked it to the adaptive value of male orgasm, I argue that the attribution of the theory as we understand it to Symons is based on a serious and hitherto unrecognised misinterpretation. Symons (...) had a different explanation of why women can orgasm, and beneath this explanation lies an obscure line of argument, including a particularly obscure use of the word ‘homologous’. (shrink)
“Functional homology” appears regularly in different areas of biological research and yet it is apparently a contradiction in terms—homology concerns identity of structure regardless of form and function. I argue that despite this conceptual tension there is a legitimate conception of ‘homology of function’, which can be recovered by utilizing a distinction from pre-Darwinian physiology (use versus activity) to identify an appropriate meaning of ‘function’. This account is directly applicable to molecular developmental biology and shares a connection to the theme (...) of hierarchy in homology. I situate ‘homology of function’ within existing definitions and criteria for structural assessments of homology, and introduce a criterion of ‘organization’ for judging function homologues, which focuses on hierarchically interconnected interdependencies (similar to relative position and connection for skeletal elements in structural homology). This analysis of biological concepts has at least three broad philosophical consequences: (1) it provides the grounds for the study of behavior and psychological categories as homologues; (2) it demonstrates that philosophers who take selected effect function as primary effectively ignore large portions of comparative, structural, and experimental research, thereby misconstruing biological reasoning and knowledge; and, (3) it underwrites causal generalizations, which illuminates inferences made from model organisms in experimental biology. (shrink)
The aim of this article is to detail some reservations against the beliefs, claims, or presuppositions that current essentialist natural kind concepts (including homeostatic property cluster kinds) model grouping practices in the life sciences accurately and generally. Such concepts fit reasoning into particular preconceived epistemic and semantic patterns. The ability of these patterns to fit scientific practice is often argued in support of homeostatic property cluster accounts, yet there are reasons to think that in the life sciences kind concepts exhibit (...) a diversity of grouping practices that are flattened out by conceptualizing them as natural kinds. Instead this article argues that the process of understanding grouping practices needs to start from a more neutral position independent of any ontological account. Following Love (Acta Biotheor 57:51–75, 2009) this paper suggests that typical natural kind concepts should be broached in the first place as grouping strategies that use a variety of semantic and epistemic tactics to apply group-bound information to tasks of explanation and understanding. (shrink)
Many of the current comparisons of taxic phylogenetic and biological homology in the context of morphology focus on what are seen as categorical distinctions between the two concepts. The first, it is claimed, identifies historical patterns of conservation and variation relating taxa; the second provides a causal framework for the explanation of this conservation and variation. This leads to the conclusion that the two need not be placed in conflict and are in fact compatible, having non-competing epistemic purposes or mapping (...) the same extensions in the form of monophyletic groupings (see Roth, The biological basis of homology 1–26, 1988; Sluys, J Zool Syst Evol Res 34:145–152, 1996; Abouheif, Trends Ecol Evol 12:405–408, 1997; Brigandt, J Exp Zool 299:9–17, 2003, Biol Philos 22:709–725, 2007; Assis and Brigandt, Evol Biol 36:248–255, 2009). This article argues that moves in this direction miss the essential disagreement between these concepts as they have been developed in the context of the debate concerning the best concept for evolutionary investigation. We should rather see these concepts employing a common fundamental methodological approach to homology, but disagreeing about how to apply the methodology effectively. Both concepts employ class reasoning, which pursues homologies as units of generalization—more precisely, as sources of reliable and relevant group-bound information in the form of shared underlying causes. The dispute can be better understood by two poles that structure such reasoning: the need for a reliable basis for projections about the causal history of shared structures, and the desire to identify homologous characters with more informative and specific causal information relevant to generalizing about evolutionary processes. Judgments in favor of one or the other in turn have affected the scope or extension of these competing homology concepts. (shrink)
The specialization of visual function within biological function is reason for introducing “homology thinking” into explanations of the visual system. It is argued that such specialization arises when organisms evolve by differentiation from their predecessors. Thus, it is essentially historical, and visual function should be regarded as a lineage property. The colour vision of birds and mammals do not function the same way as one another, on this account, because each is an adaptation to special needs of the visual functions (...) of predecessors—very different kinds of predecessors in each case. Thus, history underlies function. We also see how homology thinking figures in the hierarchical classification of visual systems, and how it supports the explanation of visual function by functional role analysis. (shrink)