Final Report Summary - NEWSYN (Internalist vs externalist evolutionary biology: do we need a New Synthesis?)
(a) Objectives
Embryology was excluded from the theory of evolution at the beginning of the 20th century, during the formulation of the Modern Synthesis (Hamburger, 1980). Claims for the integration of development into the theory of evolution have characterized significant theoretical work of the last decades. The main objectives of the project were: 1) to address the possible need for a new evolutionary synthesis, 2) if so, to explain its impact at the empirical level.
(b) Main Results
Regarding the first objective, I have outlined the existence of a deep dichotomy in the study of organic form. This dichotomy represents two different views for the integration of development and evolution. I have outlined this dichotomy, relating it to the well known preformationism/epigenesis controversy from the XVIII century, at the outset of biology. I pointed out that their views of the nature of matter, on which the logical structure of these two evolutionary perspectives has been constructed, are their crucial difference. This insight enabled me to outline fundamental philosophical differences between these views and some of their most important historical manifestations (Linde-Medina, 2010a; Linde-Medina, 2010b; Newman and Linde-Medina, 2012; Linde-Medina, 2012).
Regarding the second objective, I have contrasted these two viewpoints at the empirical level, both on the limb and in the bird beak. My study on the limb was based on the published literature, where the pioneering works on limb development in the physicalist tradition published by Prof Newman (my external supervisor) and his coworkers helped me to better understand the subject (Linde-Medina, 2011). In this work I also analyzed the various uses of the term “adaptation” and proposed a new definition that could resolve some of the main conceptual controversies surrounding it.
I also contrasted these viewpoints based on my own empirical work on beak development. Abrupt, qualitative shape variation, like curved and cross beaks resembling those observed in nature (e.g. parrots, hawks or crossbills) can be induced in the chicken embryo by exposure to certain teratogens. These morphological novelties cannot be explained by available developmental models, which assume that abrupt forms would only appear by accumulation, through many cycles of natural selection, of small and arbitrary morphological variation (Abzhanov et al., 2004; Abzhanov et al., 2006; Wu et al., 2006; Mallarino et al., 2011). We have studied the developmental cause of a parrot-like beak in the chicken embryo by analyzing the transformations of the face in control and valproic acid-treated embryos. By using 2D landmark-based geometric morphometrics methods we have shown that the formation of a curved beak at late stages (E10 to E12) is preceded by a reduction in the extension of the facial buds from stages E5 to E7, and a less protruded beak at intermediate stages (E8-E9). We have suggested a new mechanism by which a reduction in bud expansion can generate a curved beak. Actually, we are devising a new 2D in silico model incorporating this information, along with experimentally identified cellular properties functions and known viscoelastic behaviors of tissues for testing out hypothesis. This would represent the first mathematical model for the bird beak.
I have also studied the evolution of the skull shape in the order Galliformes (from which the chicken, Gallus gallus, belongs). Using 3D landmark-based geometric morphometrics methods in a recently developed comparative framework (Klingenberg and Marugán-Lobón, 2013), I have shown that the skull of Galliformes displays some of the main evolutionary patterns described in bird so far (Marugán-Lobón and Buscalioni, 2006; Kulemeyer et al., 2009; Marugán-Lobón and Buscalioni, 2009; Klingenberg and Marugán-Lobón, 2013). The fact that these evolutionary patterns have been observed in distant related species with dissimilar lifestyles (Klingenberg & Marugán-Lobón 2013) suggests that the cause of their origination would not be directly related to the current functional demands (as it is usually assumed, Kulemeyer et al., 2009), but due to the internal organization of the skull (how the skull is generated during development). I have suggested some possible mechanisms interpreting the results in the context of craniofacial development.
(c) Conclusions
Evolutionary developmental biology, or evo-devo, is a new and fast growing discipline (Gilbert et al., 1996; Arthur, 2002) which still lacks of a well developed conceptual framework (Hall 2000; Gilbert 2003). I distinguish two “evo-devos” (Linde-Medina, 2010b) and suggest that these two versions reflect the externalist-internalist dichotomy (Linde-Medina, 2010a). As Hall (Hall, 2000) has proposed, the need to distinguish them could be of great importance to evolutionary theory. While one version can be considered a subdiscipline of an Extended Evolutionary Synthesis (EES) (Pigliucci and Müller, 2010), the second one is a different interpretation of evolution (Newman, 2012).
I have shown that an induced curved beak in the chicken embryo, resembling that of other bird genera (e.g. parrots), is the result of the physical forces between facial buds and cannot be explained solely in terms of the molecular patterning and differentiation of the skeletal elements in an individual bud (Abzhanov et al., 2004; Abzhanov et al., 2006; Mallarino et al., 2011). This result illustrates the principal idea of physicalist evo-devo, i.e. genes are not the sufficient cause of form, they ‘act’ indirectly by the physical processes they mobilize (Newman, 2012; Newman and Linde-Medina, 2012; Linde-Medina and Newman, 2013).
In the study of the skull of Galliformes, I have also outlined how to integrate development into evolutionary studies.
(d) Impact
Regarding the empirical findings, I believe our results on the chicken embryo would open a new perspective for approaching the study of development and evolution of the bird beak, a paradigmatic example in evolutionary biology.
Regarding the theoretical findings, the Darwinian framework has been extensively applied to different fields, its purported power of explanation being compared to a “universal acid” (Dennett, 1995). For this reason, a change in the foundations of evolutionary biology would have a significant impact on both the sciences and the humanities (Fodor and Piattelli-Palmarini, 2010). Some of my work have already been discussed by researchers working in biolinguistics and biosemiotics (Boeckx and Longa, 2011; Barbieri, 2012).
Reference List
Abzhanov A, Kuo WP, Hartman C, Grant R, Grant P, Tabin CJ (2006) The calmodulin pathway and evolution of elongated beak morphology in Darwin's finches. Nature 442:563-567
Abzhanov A, Protas M, Grant R, Grant P, Tabin CJ (2004) Bmp4 and morphological variation of beaks in Darwin's finches. Science 305:1462-1465
Arthur W (2002) The emerging conceptual framework of evolutionary developmental biology. Nature 415:757-764
Barbieri M (2012) Code Biology: A New Science of Life. Biosemiotics 5:411-437
Boeckx C, Longa VM (2011) Lenneberg's views on language development and evolution and their relevance for modern biolinguistics. Biolinguistics 5:254-273
Dennett DC (1995) Darwin's dangerous idea: evolution and the meanings of life. Simon & Schuster, New York
Fodor JA, Piattelli-Palmarini M (2010) What Darwin got wrong. Farrar, Straus and Giroux, New York
Gilbert S, Opizt JM, Raff RA (1996) Resynthesizing evolutionary and developmental biology. Dev Biol 173:357-372
Hall BK (2000) Evo.Devo or devo-evo - does it matter? Evol Dev 2:177-178
Hamburger V (1980) Embriology and the Modern Synthesis in evolutionary theory. In: Mayr E, Provine W (eds) The Evolutionary Synthesis. Harvard University Press, Cambridge, MA, pp. 97-112
Klingenberg CP, Marugán-Lobón J (2013) Evolutionary Covariation in Geometric Morphometric Data: Analyzing Integration, Modularity and Allometry in a Phylogenetic Context. Syst Biol in press:
Kulemeyer C, Asbahr K, Gunz P, Frahnert S, Bairlein F (2009) Functional morphology and integration of corvid skulls - a 3D geometric morphometric approach. Frontiers in Zoology 6:2
Linde-Medina M (2010a) Natural selection and self-organization: a deep dichotomy in the study of organic form. Ludus Vitalis XVIII:25-56
Linde-Medina M (2010b) Two "EvoDevos". Biol Theor 5:7-11
Linde-Medina M (2011) Adaptation or exaptation? The case of the human hand. J Bioesciences 36:575-585
Linde-Medina M (2012) Reply to the comments on "Natural selection and self-organization: a deep dichotomy in the study of organic form. Ludus Vitalis XIX:387-397
Linde-Medina M, Newman SA (2013) Limb, tooth, beak: three modes of development and evolutioanry innovation of form. J Bioesciences in press:
Mallarino R, Grant PR, Grant BR, Herrel A, Kuo WP, Abzhanov A (2011) Two developmental modules establish 3D beak-shape variation in Darwin's finches. PNAS 108:4057-4062
Marugán-Lobón J, Buscalioni ÁD (2006) Avian skull morphological evolution: exploring exo- and endocranial covariation with two-block partial least squares. Zoology 109:217-230
Marugán-Lobón J, Buscalioni ÁD (2009) New Insight on the Anatomy and Architecture of the Avian Neurocranium. The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology 292:364-370
Newman SA (2012) The developmental specifity of physical mechanisms. Ludus Vitalis XIX:343-351
Newman SA, Linde-Medina M (2012) Physical determinants in the emergence and inheritance of multicellular form. Biol Theor (in press)
Pigliucci M, Müller GB (2010) Evolution - The extended synthesis. MIT Press,
Wu P, Jiang TX, Shen JY, Widelitz RB, Chuong CM (2006) Morphoregulation of avian beaks: comparative mapping of growth zone activities and morphological evolution. Dev Dyn 235:1400-1412
Embryology was excluded from the theory of evolution at the beginning of the 20th century, during the formulation of the Modern Synthesis (Hamburger, 1980). Claims for the integration of development into the theory of evolution have characterized significant theoretical work of the last decades. The main objectives of the project were: 1) to address the possible need for a new evolutionary synthesis, 2) if so, to explain its impact at the empirical level.
(b) Main Results
Regarding the first objective, I have outlined the existence of a deep dichotomy in the study of organic form. This dichotomy represents two different views for the integration of development and evolution. I have outlined this dichotomy, relating it to the well known preformationism/epigenesis controversy from the XVIII century, at the outset of biology. I pointed out that their views of the nature of matter, on which the logical structure of these two evolutionary perspectives has been constructed, are their crucial difference. This insight enabled me to outline fundamental philosophical differences between these views and some of their most important historical manifestations (Linde-Medina, 2010a; Linde-Medina, 2010b; Newman and Linde-Medina, 2012; Linde-Medina, 2012).
Regarding the second objective, I have contrasted these two viewpoints at the empirical level, both on the limb and in the bird beak. My study on the limb was based on the published literature, where the pioneering works on limb development in the physicalist tradition published by Prof Newman (my external supervisor) and his coworkers helped me to better understand the subject (Linde-Medina, 2011). In this work I also analyzed the various uses of the term “adaptation” and proposed a new definition that could resolve some of the main conceptual controversies surrounding it.
I also contrasted these viewpoints based on my own empirical work on beak development. Abrupt, qualitative shape variation, like curved and cross beaks resembling those observed in nature (e.g. parrots, hawks or crossbills) can be induced in the chicken embryo by exposure to certain teratogens. These morphological novelties cannot be explained by available developmental models, which assume that abrupt forms would only appear by accumulation, through many cycles of natural selection, of small and arbitrary morphological variation (Abzhanov et al., 2004; Abzhanov et al., 2006; Wu et al., 2006; Mallarino et al., 2011). We have studied the developmental cause of a parrot-like beak in the chicken embryo by analyzing the transformations of the face in control and valproic acid-treated embryos. By using 2D landmark-based geometric morphometrics methods we have shown that the formation of a curved beak at late stages (E10 to E12) is preceded by a reduction in the extension of the facial buds from stages E5 to E7, and a less protruded beak at intermediate stages (E8-E9). We have suggested a new mechanism by which a reduction in bud expansion can generate a curved beak. Actually, we are devising a new 2D in silico model incorporating this information, along with experimentally identified cellular properties functions and known viscoelastic behaviors of tissues for testing out hypothesis. This would represent the first mathematical model for the bird beak.
I have also studied the evolution of the skull shape in the order Galliformes (from which the chicken, Gallus gallus, belongs). Using 3D landmark-based geometric morphometrics methods in a recently developed comparative framework (Klingenberg and Marugán-Lobón, 2013), I have shown that the skull of Galliformes displays some of the main evolutionary patterns described in bird so far (Marugán-Lobón and Buscalioni, 2006; Kulemeyer et al., 2009; Marugán-Lobón and Buscalioni, 2009; Klingenberg and Marugán-Lobón, 2013). The fact that these evolutionary patterns have been observed in distant related species with dissimilar lifestyles (Klingenberg & Marugán-Lobón 2013) suggests that the cause of their origination would not be directly related to the current functional demands (as it is usually assumed, Kulemeyer et al., 2009), but due to the internal organization of the skull (how the skull is generated during development). I have suggested some possible mechanisms interpreting the results in the context of craniofacial development.
(c) Conclusions
Evolutionary developmental biology, or evo-devo, is a new and fast growing discipline (Gilbert et al., 1996; Arthur, 2002) which still lacks of a well developed conceptual framework (Hall 2000; Gilbert 2003). I distinguish two “evo-devos” (Linde-Medina, 2010b) and suggest that these two versions reflect the externalist-internalist dichotomy (Linde-Medina, 2010a). As Hall (Hall, 2000) has proposed, the need to distinguish them could be of great importance to evolutionary theory. While one version can be considered a subdiscipline of an Extended Evolutionary Synthesis (EES) (Pigliucci and Müller, 2010), the second one is a different interpretation of evolution (Newman, 2012).
I have shown that an induced curved beak in the chicken embryo, resembling that of other bird genera (e.g. parrots), is the result of the physical forces between facial buds and cannot be explained solely in terms of the molecular patterning and differentiation of the skeletal elements in an individual bud (Abzhanov et al., 2004; Abzhanov et al., 2006; Mallarino et al., 2011). This result illustrates the principal idea of physicalist evo-devo, i.e. genes are not the sufficient cause of form, they ‘act’ indirectly by the physical processes they mobilize (Newman, 2012; Newman and Linde-Medina, 2012; Linde-Medina and Newman, 2013).
In the study of the skull of Galliformes, I have also outlined how to integrate development into evolutionary studies.
(d) Impact
Regarding the empirical findings, I believe our results on the chicken embryo would open a new perspective for approaching the study of development and evolution of the bird beak, a paradigmatic example in evolutionary biology.
Regarding the theoretical findings, the Darwinian framework has been extensively applied to different fields, its purported power of explanation being compared to a “universal acid” (Dennett, 1995). For this reason, a change in the foundations of evolutionary biology would have a significant impact on both the sciences and the humanities (Fodor and Piattelli-Palmarini, 2010). Some of my work have already been discussed by researchers working in biolinguistics and biosemiotics (Boeckx and Longa, 2011; Barbieri, 2012).
Reference List
Abzhanov A, Kuo WP, Hartman C, Grant R, Grant P, Tabin CJ (2006) The calmodulin pathway and evolution of elongated beak morphology in Darwin's finches. Nature 442:563-567
Abzhanov A, Protas M, Grant R, Grant P, Tabin CJ (2004) Bmp4 and morphological variation of beaks in Darwin's finches. Science 305:1462-1465
Arthur W (2002) The emerging conceptual framework of evolutionary developmental biology. Nature 415:757-764
Barbieri M (2012) Code Biology: A New Science of Life. Biosemiotics 5:411-437
Boeckx C, Longa VM (2011) Lenneberg's views on language development and evolution and their relevance for modern biolinguistics. Biolinguistics 5:254-273
Dennett DC (1995) Darwin's dangerous idea: evolution and the meanings of life. Simon & Schuster, New York
Fodor JA, Piattelli-Palmarini M (2010) What Darwin got wrong. Farrar, Straus and Giroux, New York
Gilbert S, Opizt JM, Raff RA (1996) Resynthesizing evolutionary and developmental biology. Dev Biol 173:357-372
Hall BK (2000) Evo.Devo or devo-evo - does it matter? Evol Dev 2:177-178
Hamburger V (1980) Embriology and the Modern Synthesis in evolutionary theory. In: Mayr E, Provine W (eds) The Evolutionary Synthesis. Harvard University Press, Cambridge, MA, pp. 97-112
Klingenberg CP, Marugán-Lobón J (2013) Evolutionary Covariation in Geometric Morphometric Data: Analyzing Integration, Modularity and Allometry in a Phylogenetic Context. Syst Biol in press:
Kulemeyer C, Asbahr K, Gunz P, Frahnert S, Bairlein F (2009) Functional morphology and integration of corvid skulls - a 3D geometric morphometric approach. Frontiers in Zoology 6:2
Linde-Medina M (2010a) Natural selection and self-organization: a deep dichotomy in the study of organic form. Ludus Vitalis XVIII:25-56
Linde-Medina M (2010b) Two "EvoDevos". Biol Theor 5:7-11
Linde-Medina M (2011) Adaptation or exaptation? The case of the human hand. J Bioesciences 36:575-585
Linde-Medina M (2012) Reply to the comments on "Natural selection and self-organization: a deep dichotomy in the study of organic form. Ludus Vitalis XIX:387-397
Linde-Medina M, Newman SA (2013) Limb, tooth, beak: three modes of development and evolutioanry innovation of form. J Bioesciences in press:
Mallarino R, Grant PR, Grant BR, Herrel A, Kuo WP, Abzhanov A (2011) Two developmental modules establish 3D beak-shape variation in Darwin's finches. PNAS 108:4057-4062
Marugán-Lobón J, Buscalioni ÁD (2006) Avian skull morphological evolution: exploring exo- and endocranial covariation with two-block partial least squares. Zoology 109:217-230
Marugán-Lobón J, Buscalioni ÁD (2009) New Insight on the Anatomy and Architecture of the Avian Neurocranium. The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology 292:364-370
Newman SA (2012) The developmental specifity of physical mechanisms. Ludus Vitalis XIX:343-351
Newman SA, Linde-Medina M (2012) Physical determinants in the emergence and inheritance of multicellular form. Biol Theor (in press)
Pigliucci M, Müller GB (2010) Evolution - The extended synthesis. MIT Press,
Wu P, Jiang TX, Shen JY, Widelitz RB, Chuong CM (2006) Morphoregulation of avian beaks: comparative mapping of growth zone activities and morphological evolution. Dev Dyn 235:1400-1412