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Tracing homologies in an ever-changing world

Trovare le omologie in un mondo in continua evoluzione
Alessandro Minelli
p. 40-55


A un secolo e mezzo dalla pubblicazione dell'Origine delle specie, la nozione di omologia di Owen, che implica che due organi o due funzioni a confronto possono essere riconosciuti come “la stessa cosa” continua a dominare gli attuali approcci al problema dell’omologia. L'idea che i caratteri possano “rimanere se stessi” attraverso un numero indefinito (anche se finito) di stati alternativi che si susseguono nel corso dell'evoluzione è probabilmente basato su un'interpretazione idealistica di come gli organismi si evolvono. Se si dà per scontata l'esistenza di caratteristiche del corpo che conservano la loro identità nel cambiamento, l'esistenza di omologhi può essere spiegata (i) in termini di leggi universali della forma, magari nella forma moderna dello strutturalismo di processo, o (ii) come il prodotto di discendenza comune, o (iii) in termini di cause prossime responsabili della comparsa di moduli di sviluppo conservati. Tuttavia, leggendo la storia della vita attraverso la lente dell’evoluzione, appare molto problematico descrivere un organismo come una somma di caratteri che, una volta apparsi come novità evolutive, rimangono poi come unità costruttive essenzialmente immutabili tra le quali possiamo predicare (o negare) omologia. Tutti i tratti sono meglio interpretati come incroci complessi e mutevoli di un numero indeterminato di elementi e dei processi che li modellano nel corso dell’ontogenesi e della filogenesi. Di conseguenza, appare raccomandabile un approccio fattoriale, o combinatorio, all’omologia.

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Testo integrale

1. The homologue as a given

1A name – Empedocles – occurs quite frequently in the recurrent search for evidence of evolutionary thought among the philosophers and naturalists of past centuries. Empedocles imagined a world full of body parts such as heads and limbs, constantly subject to the opposite forces of Love and Strife. Love tends to combine these parts together, but only some of the resulting associations are robust enough to survive the disrupting attacks of Strife. To some extent this world can be compared to a Darwinian system in which natural selection operates, a world of winners and losers in the daily confrontation with the environment.

2There are, however, two important differences between the mythical world of Empedocles and the Darwinian world dominated by natural selection. The first difference is the lack, in the old philosopher’s worldview, of a principle of inheritance. To be sure, we should not expect Empedocles to have articulated a plausible model to explain the transmission of traits across generations (Darwin did, eventually along a wrong line of thought), but the fact remains that in Empedocles’ world all combinations of body parts, stable and unstable alike, are unceasingly formed anew by combination of elementary units.

3But it is right in the way these units are conceived – this is the second issue – that we measure the distance between Empedocles’ vision and a really evolutionary thought. Heads, limbs and other primordial parts are given, unchanging, atemporal, eternal perhaps. To the contrary, nothing in nature – in the living nature especially – escapes change, nothing can be taken as given. It is not simply that sometimes around 260 million years ago, in the lineage eventually leading to flies and mosquitoes the hindwings, membranous until then, where changed into pin-like devices, the halters, used to stabilize flight. Insect hindwings, and wings generally, are also something that, in turn, has came into being during the evolution of a particular (and eventually very successful) lineage of arthropods. On the other hand, in the course of the evolution of the dipterans, the halters have taken a diversity of shapes. Same with every feature in all lineages of living beings.

  • 1 Owen 1843: 379.
  • 2 Wagner 2014: 40.
  • 3 Ivi: 42-3.

4And thus, most of the current approaches to homology seem to be closer to Empedocles’ views than to a consequent evolutionary description of the living world. One century and half after the publication of Darwin’s Origin, it seems difficult indeed that we can still be satisfied with Owen’s notion, according to which homologue is the same organ in different animals under every variety of form and function1. Despite the indeterminacy and subjectivity of the criterion of «sameness» to which Owen appealed to decide about the homology of two organs (or features) under comparison, the notion that these can be recognized as «the same» is still firmly with us and apparently continues to dominate the current approaches to the problem of homology. In most instances, this assumption of “sameness” is only implicit, although arguably obligate, so long as homology is conceived as an all-or-nothing relationship, but sometimes it is explicitly spelled out in full. Here is an example: «There are numerous examples of corresponding characters between species for which it is hard to escape the conclusion that organisms from different species are clearly composed of the same building blocks, such as heads, limbs and brains»2. These are the body parts we can trace as homologous in comparing one species to another: «Any character that can be homologized is assumed to have continuity in terms of its existence in a lineage of descent, as well as persistence of differences from other parts of the body (individuality)»3. The only possible restriction, albeit an indirect and indeterminate one, to the otherwise unlimited temporal extension of these “unchanging” body parts is the reference to a specific “lineage of descent” – but this opens an additional question. Homologues are not eternal but, according to a very popular view, they emerge as «evolutionary novelties» without an homologue in the ancestral lineage from which they emerge.

  • 4 Cf. e.g., Müller and Wagner 1991, 2003; Newman and Müller 2005; Shubin et al. 2009.
  • 5 West-Eberhard 2008: 198.
  • 6 For a similar view see Minelli and Fusco 2005.
  • 7 von Baer 1828, I: 156.

5Evolutionary novelties, and the process of innovation of which these are assumed to be the outcome, are popular concepts in evo-devo4. The question is, how novelty can be defined. According to West-Eberhard, a novelty is a phenotypic trait that is new in composition or context of expression relative to established ancestral traits5. This definition has some obvious merit. First, it acknowledges that even the best characterized feature is a composite results of a multiplicity of traits, some of which can be traced to homologous traits of remote ancestors, others are more recent, while “novelty” cannot be predicated of any feature as a whole6: nirgends ist Neubildung, sondern nur Umbildung7.

  • 8 Müller 1990: 101.
  • 9 As noted e.g. by Moczek 2008.
  • 10 Hall 2005: 549.
  • 11 See Brigandt and Love 2010.
  • 12 Donoghue 1992; Wake 2003; Moczek 2008.
  • 13 Minelli 2003; West-Eberhard 2003.

6More popular are other definitions of novelty, such as a qualitatively new structure with a discontinuous origin8. However, the line separating quantitative from qualitative differences is hardly an absolute one9. The obvious link between the notion of novelty and the conventional (all-or-nothing) notion of homology was made clear by Hall, who defined a novelty as a new feature in a group of organisms that is not homologous to a feature in an ancestral taxon10. However11, this strategy is probably illusory because the meaning of homology is also controversial12. If homology is a matter of degree13, as I will suggest below, we must also accept that there is a continuum between non-novelty and novelty.

  • 14 Wagner 2014: 43.
  • 15 Abzhanov et al. 2004, 2006.

7To be sure, even the staunchest defenders of an all-or-nothing concept of homology are well aware of the variety of form and function under which their homologues occur. Wagner is quite explicit on this subject: we have two distinct phenomena to explain. We distinguish between the origin of homologs (i.e., “novelties’” and their modification by natural selection (i.e., adaptation). The former is studied in developmental evolution, whereas the latter is studied in functional morphology, ecological genetics, life history theory, and other branches of evolutionary theory14. Is this distinction justified? I do not think so. There are very good examples of research in “developmental evolution” that explain the mechanism underlying the evolution of morphological differences among closely related species in an obvious homologue, the bill of birds: variation in bill size among the geospizines (Darwin’s finches) of the Galápagos Islands is a textbook example of recent divergence, the core feature of an adaptive radiation, but it is also a test case of the importance of evolutionary developmental biology in showing how, and to which extent, a given feature can evolve, by showing how and under which constraints are produced the alternative phenotypes upon which natural selection will eventually operate15.

2. Homology – given, only to be explained

  • 16 Minelli et al. 2006; Minelli and Fusco 2013.

8Eventually, the idea that characters can “remain themselves” throughout an indefinite number of possible alternative states that follow one another in the course of evolution is probably based on an idealistic interpretation of how organisms evolve16.

9This explains the range of strategies used by the majority of authors in addressing the problem of homology. If the existence of body features that are “the same” is takes as “given”, then the existence of homologues can be explained according to one of the following lines: (i) in terms of “universal laws” of form, (ii) as the product of common ancestry, or (iii) in terms of proximal causes responsible for the emergence of conserved developmental modules.

  • 17 Cf. Goodwin 1977.
  • 18 Resnik 1994. The most articulated, book-size expression of this approach is Webster and Goodwin 199 (...)

10The search for unknown but putatively existent universal laws of form was cognate to Wilhelm Roux’s effort to articulate a developmental mechanics (Entwicklungsmechanik) of the living organisms17, but has surfaced again in the late xx century, under the name of process structuralism18.

  • 19 Newman and Comper 1990, Forgacs and Newman 2005, Newman et al. 2006.
  • 20 Striedter 1998: 219.

11More recently, Stuart Newman19 has vigorously defended the idea that in early stages of the evolution of metazoans the emerging shapes of multicellular systems were dominated by the physical (mechano-elastic) properties of the living matter, arguably sufficient to determine the production of a set of generic forms such as hollow spheres and segmented beads. A conceptually fascinating bridge between this physicalist or structuralist approach and the issue of homology has emerged meanwhile, in so far as we can describe development [a]s the trajectory of a complex physical system with multiple stable states [while] homologous characters are features that appear reliably within that system as it perpetuates itself across generations. By analogy with stable emergent features in other complex dynamical systems, these recurring developmental features may be called recurring “attractors”. Because attractors do not pre-exist within a system before they emerge, the conceptualization of homologues as recurring attractors is here identified as the epigenetic concept of homology20.

12The main problem with these physicalist and structuralist approaches is the very limited range of biological forms to which they apply – forms comparable to the simple geometric structure of early embryos, whereas the whole range of organ and body shapes that are the actual concern of the comparative morphology remain far beyond the reach.

  • 21 Mayr 1969: 85. This was reformulated by Bock (1974) in the following terms: «Features (or condition (...)

13This explains the limited interest towards these approaches shown by the majority of biologists working on complex animal or plant structures, including anatomists, embryologists and especially systematists. In their fields, the mainstream attitude towards the issue of homology rotates around the historical concept of homology as exemplified by Mayr’s definition: homologous features (or states of features) in two or more organisms are those that can be traced back to the same feature (or state) in the common ancestor of those organisms21.

  • 22 Hennig 1966; see also Id. 1965.
  • 23 Roth 1984, 1988; Minelli and Peruffo 1991; Minelli 1996.
  • 24 This umbrella term was introduced by Minelli and Fusco 2013.
  • 25 Wagner 1989: 62.
  • 26 Wagner and Misof 1993; Wagner 1994.
  • 27 Wagner 1996. In a further revisitation of the problem, however, Müller and Wagner (1996: 4) adopted (...)

14Some thirty years since the modern phylogenetic revisitation of the historical concept of homology has became to spread, starting with the publication of Hennig’s best known monograph22, several biologists, while still convinced of the usefulness of a concept of homology but dissatisfied with the prevailing historical approach, started looking for an alternative foundation. This effort23 lead to the proposal of a number of proximal-cause concepts of homology24. In Wagner’s (1989) original formulation, [s]tructures from two individuals or from the same individual are homologous if they share a set of developmental constraints, caused by locally acting self-regulatory mechanisms of organ differentiation. These structures are thus developmentally individualized parts of the phenotype25. In subsequent papers26, Wagner refined this concept of developmental individualization, rephrasing it in terms of independent units of developmental control, due to either morphogenetic or morphostatic constraints, finally adding that homologues can be understood as modular units of evolutionary transformation27.

3. Of eggs and fossils

15In historical sciences – and biology makes no exception – persistent problems stem from a biased perspective unduly focussing on a state of the system which is considered as the “final”, unavoidable target of the process we are about to reconstruct.

  • 28 Discussed at length in Minelli 2003, 2011, 2013, 2014.

16In biology, especially but not exclusively in developmental biology, this state is very often the adult. All other states are seen as preparatory to it. Most of the popular definitions of development take this state as the natural end-point of a process starting with a not less arbitrary beginning, i.e. the egg. This adultocentric perspective on development28 causes the persistence of an unwarranted amount of finalism and, not less serious, ignores a number of basic aspects of cellular, evolutionary and developmental biology. I will mention here only a couple of them.

17To be sure, fertilization is often a suitable point from which to start the study of a developmental sequence. In most animals, indeed, penetration of the male nucleus into the ripe but unfertilized egg releases a predictable chain of events such as cleavage, gastrulation etc., eventually leading to the adult. We should refrain, however, from taking for granted that the egg stage is the ‘real’ beginning of development, and also from considering the eventual achievement of the adult form as the obligate product of development.

  • 29 Boyden and Shelswell 1959.

18The egg is not a primitive cell, but one of the most specialized of all cell types29, witnesses its often enormous size due to the stored yolk and its frequent specialized envelopes. In evolutionary terms, the hen’s egg is not necessarily older than the hen.

  • 30 Raup 1979.
  • 31 Behrensmeyer 1988.

19Another field where serious problems are due to the well-entrenched habit of moving from the most easily observable facts back into increasingly older states of the system is palaeontology, which is frequently biased by the so-called pull of the recent: our knowledge of modern organisms is much more complete and detailed than our knowledge of their predecessors of any time in the past30. As a consequence, much of what we know about the taxonomic and ecological diversity of living species, about their metabolism, development, reproduction and evolution ends up shaping the way we interpret the extinct ones. This bias, progressively more threatening the more we move back into the past, may cause serious distortions to our reconstruction of the history of life, of the long trends in the deployment of biodiversity, of the composition and dynamics of the biocenoses of remote times31.

  • 32 E.g., Gould 1989.
  • 33 E.g., Conway Morris 2003.
  • 34 Darwin 1859: 472.

20Eventually, two opposite worldviews have been confronted in the reconstruction of the past. On the one side, a view of the history of life dominated by contingency, and thus completely unpredictable32; on the other side, a view of the history of life running along somehow predictable paths, an argument apparently supported by the frequent recurrence of convergence and by the broad similarity of biocenoses (in terms of «filled niches», if not in terms of lineages actually filling them) before and after a mass extinction33. Evidence in these matters notwithstanding, it is not easy to accept as free from the pull of the Recent any argument expressed in terms of empty niches, of unoccupied or ill-occupied place[s] in nature34.

4. Did Romulus found Rome?

21According to the old story, Rome was founded by Romulus. A product of history called for the existence of someone who must have put the process in motion. The truth, of course, is just the opposite: it was Rome (that is, Romans) that created (the myth of) Romulus. This way, we would never know how a town comes eventually into being. We will never understand the complex and only partially predictable dynamics ruling a local community of humans, among the ecological effects of which is a modification of the landscape into something we will eventually call a town. To penetrate into these aspects of the history of human civilization, we shall move from the past rather than from the present; from simple systems rather than from “mature” ones; from arbitrarily but consciously and rationally selected beginnings, thus taking distance from mythical «origins» that purport to identify precise beginnings, or a temporal singularity: an unambiguous time zero, at which ex abrupto, if not ex nihilo, the system came into existence.

22The beginnings we actually need to fix, to allow us moving across time, are similar to those of a traditional fairy tale: Once upon the time there was a beautiful princess. She lived in a castle together with her father the king… To be sure, nobody assumes that the king was the first of humans there, neither that the castle was not built by someone by putting stone over stone… But the narrator is not interested in those older people and events, neither is its audience expected to be. The narrative moves from an arbitrary but conveniently selected instant in the past and runs according to the arrow of time. Facts are expected to depend, to some extent at least, from conditions in the past, including the possible presence of figures such as fairies and witches. Were it not for the unpredictable behaviour of the latter, the structure of this narrative is not that different from the description of natural events in a classic Newtonian framework. The observer circumscribes the system to be studied by arbitrarily but conveniently fixing temporal and spatial initial conditions. This is when and where the story will begin. The observer will measure the changes of a number of variables through time and the system’s condition at time Tj will be eventually explained as dependent on those at a previous time Ti, under the operation of one or more functions linking the measured variables together through time.

  • 35 Gayon 1992.

23By disposing of the traditional framing of questions in terms of origins and progress and finally emerging as a real “science of change”, evolutionary biology has been forced to identify the “zero condition” of its subject phenomena. In terms of population genetics, a population in Hardy-Weinberg equilibrium represents the “inertial system”35, the zero condition from which we can move. Our actual interest in that population will begin at the time it will move away from the equilibrium.

24Of course, knowledge of a causal law may invite using it retrodictively, to infer previous states from later ones, but this is a dangerous path, if the system in which we are interested is more complex than an elementary mechanical system. Retrodictions about an ecosystem or a living organism do not have many chances of being reliable except for broad traits.

  • 36 On the persistence of adaptationism in current biological literature, see Caruso et al. 2012.

25Of the many pitfalls awaiting the biologist who follows the arrow of time backwards, the most insidious are probably the insistence on evolutionary innovations, briefly discussed above, and a wrong perspective on adaptation36.

  • 37 In the sense of the process of change promoted by natural selection, not in the sense of the result (...)
  • 38 Coddington 1988.
  • 39 Gould and Vrba 1982.
  • 40 As noted by Gould 2002.
  • 41 Nietzsche 1887: 55.

26There are two reasons for mentioning adaptation in this context. First, its conditional, comparative nature: with the unavoidable arbitrariness with which we section phenotypes into unit characters, and processes into units phases, we can describe adaptation37as occurring in steps – each of them from a plesiomorphic functional state to an apomorphic one, exactly in the way morphological change is interpreted through the cladistic revisitation of homology38. Second, the study of adaptation is threatened by the same naïf perspective because of which excessive focus on the present forbids a correct interpretation of the past. Indeed, we have no reason for taking current function as the best, or only cue to the selective regime under which a trait has evolved. Current function may well be a product of exaptation39, a concept that was anticipated40 by Nietzsche’s admirable remark, that the origin or the emergence of a thing and its ultimate usefulness, its practical application and incorporation into a system of ends, are toto coelo separate; that anything in existence, having somehow come about, is continually interpreted anew, requisitioned anew, transformed and directed to a new purpose41.

5. Back to Rome

27Let’s move back once more to Rome. When the old citizens of Rome, and their historians, were thinking of Romulus, what did they think he had actually founded? Rome as a cluster of huts, to be eventually replaced with robust and handsome houses and villas? Or perhaps Rome as a community sharing local resources, material and cultural alike? If not, did they refer instead to Rome as a state with its laws and its rules – eventually changed when the last of the old seven kings left space for a republic, and again with the advent of the empire with Augustus and his successors?

  • 42 Minelli and Fusco 1995.
  • 43 Cf. Minelli 2009: especially 202-204.

28The same kind of questions must be addressed to comparative biologists, who all describe the living beings in terms of individual parts, but are seldom aware of the very limited extent to which, for example, the units of descriptive morphology correspond to those of functional anatomy, or those of morphogenetics42. Failing to address this problem explicitly, it is all too easy to take for granted that there must be developmental (i.e., morphogenetic) modules coextensive with obvious morphofunctional units such as a leg (or, better, a pair of legs) or a brain. This expectation, however, is totally unwarranted. Unfortunately, in many textbooks development is described as a temporal and causal sequence of steps one of which is called organogenesis. This chapter of developmental biology should show how a brain is built, or a heart, or a limb. Actually, numerous distinct processes are involved in making a brain, a heart or a limb. None of them individuates a developmental module spatially coextensive with the emerging organ, and most of them are common to a number of different body regions43.

29The modularity of developmental events can still be advocated as a property we can use to recognize homologues, but only if we are ready to dispose of the old all-or-nothing notion of development.

6. Out of the hierarchies

  • 44 Arthur 2000, 2002, 2011, 2015; Minelli 2015.

30As a rule, developmental modules are not arranged hierarchically, at least at the scale of inclusivity at which we are more interested in tracing homologies. If organs are each the product of a number of developmental dynamics, none of which is spatially restricted to a single organ (or its Anlage), it is quite improbable that the peculiar intersection (both spatial and temporal) of developmental modules out of which an organ emerges will be long conserved in evolution. To the contrary, right the opposite is what we observe, and often register under the term of heterochrony, or the conceptually associated umbrellas of heterotopy and heterometry44.

  • 45 See, e.g., Arnold et al., 1989; Minelli and Peruffo, 1991; Mabee, 1993; Arthur, 1997. The emerging (...)
  • 46 Van Valen 1982; Roth 1984; Gans 1985; Sattler 1994; Shubin and Wake 1996.
  • 47 Minelli 1998.
  • 48 Roth 1984; Haszprunar 1992; Shubin and Wake 1996; Meyer 1998; Minelli 1998, 2003; Abouheif 1999; Wa (...)

31A reaction against the traditional hierarchical view of development is increasingly voiced45. Taking distance from the traditional, all-or-nothing approach according to which two structures are either homologous or nonhomologous, since the ’80s of the past century several authors have been defending the view that all assessments of homology are by necessity partial46. Eventually, I suggested a factorial (or combinatorial) concept of homology47 and an increasing number of comparative morphologists and evolutionary biologists now accept that, because evolutionary change is a continuous process, based on the remolding of pre-existing features as well as the genetic networks that regulate and control their development, homology should be treated as relative, or partial48.

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1 Owen 1843: 379.

2 Wagner 2014: 40.

3 Ivi: 42-3.

4 Cf. e.g., Müller and Wagner 1991, 2003; Newman and Müller 2005; Shubin et al. 2009.

5 West-Eberhard 2008: 198.

6 For a similar view see Minelli and Fusco 2005.

7 von Baer 1828, I: 156.

8 Müller 1990: 101.

9 As noted e.g. by Moczek 2008.

10 Hall 2005: 549.

11 See Brigandt and Love 2010.

12 Donoghue 1992; Wake 2003; Moczek 2008.

13 Minelli 2003; West-Eberhard 2003.

14 Wagner 2014: 43.

15 Abzhanov et al. 2004, 2006.

16 Minelli et al. 2006; Minelli and Fusco 2013.

17 Cf. Goodwin 1977.

18 Resnik 1994. The most articulated, book-size expression of this approach is Webster and Goodwin 1996.

19 Newman and Comper 1990, Forgacs and Newman 2005, Newman et al. 2006.

20 Striedter 1998: 219.

21 Mayr 1969: 85. This was reformulated by Bock (1974) in the following terms: «Features (or conditions of a feature) in two or more organisms are homologous if they stem phylogenetically from the same feature (or the same condition of the feature) in the immediate common ancestor of these organisms».

22 Hennig 1966; see also Id. 1965.

23 Roth 1984, 1988; Minelli and Peruffo 1991; Minelli 1996.

24 This umbrella term was introduced by Minelli and Fusco 2013.

25 Wagner 1989: 62.

26 Wagner and Misof 1993; Wagner 1994.

27 Wagner 1996. In a further revisitation of the problem, however, Müller and Wagner (1996: 4) adopted a less deterministic approach, suggesting some degree of independence of structural homology from its genetic and developmental makeup. Since the beginning of this century, there has been a flowering of the literature about developmental module (e.g., Schlosser 2002; Schlosser and Wagner 2004; Callebaut and Rasskin-Gutman 2005). Unfortunately, reading through these works is often problematic, due to the multiple and often not defined usages of the term module (see comments by Omont and Képès 2005; Van Speybroeck 2005; Mitchell 2006). A possible definition of developmental module is a local focus where development goes on differently from what happens nearby.

28 Discussed at length in Minelli 2003, 2011, 2013, 2014.

29 Boyden and Shelswell 1959.

30 Raup 1979.

31 Behrensmeyer 1988.

32 E.g., Gould 1989.

33 E.g., Conway Morris 2003.

34 Darwin 1859: 472.

35 Gayon 1992.

36 On the persistence of adaptationism in current biological literature, see Caruso et al. 2012.

37 In the sense of the process of change promoted by natural selection, not in the sense of the resulting condition, better termed adaptedness.

38 Coddington 1988.

39 Gould and Vrba 1982.

40 As noted by Gould 2002.

41 Nietzsche 1887: 55.

42 Minelli and Fusco 1995.

43 Cf. Minelli 2009: especially 202-204.

44 Arthur 2000, 2002, 2011, 2015; Minelli 2015.

45 See, e.g., Arnold et al., 1989; Minelli and Peruffo, 1991; Mabee, 1993; Arthur, 1997. The emerging view is that there is no simple, linear hierarchical relationship between genotype, development, and the resulting phenotype. On the complexity of the genotype phenotype → map see, e.g., Alberch 1991, Pigliucci 2010, Wagner and Zhang 2011; in the context of homology, also Roth 1988, 1991; Hall 1995.

46 Van Valen 1982; Roth 1984; Gans 1985; Sattler 1994; Shubin and Wake 1996.

47 Minelli 1998.

48 Roth 1984; Haszprunar 1992; Shubin and Wake 1996; Meyer 1998; Minelli 1998, 2003; Abouheif 1999; Wake 1999; Pigliucci 2001; Minelli and Fusco 2013.

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Notizia bibliografica

Alessandro Minelli, «Tracing homologies in an ever-changing world»Rivista di estetica, 62 | 2016, 40-55.

Notizia bibliografica digitale

Alessandro Minelli, «Tracing homologies in an ever-changing world»Rivista di estetica [Online], 62 | 2016, online dal 01 septembre 2016, consultato il 30 juin 2022. URL:; DOI:

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Alessandro Minelli

Department of Biology - University of Padova

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