Old and New Concepts in EvoDevo
The concept of the modular organization of the organism is central to both classical experimental embryology and modern evolutionary developmental biology (EvoDevo). The latter discipline often ascribes homology, or the diversity of forms arising from the
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Old and New Concepts in EvoDevo Margherita Raineri
Abstract The concept of the modular organization of the organism is central to both classical experimental embryology and modern evolutionary developmental biology (EvoDevo). The latter discipline often ascribes homology, or the diversity of forms arising from the same module or combination of modules, to gene mutations or changes of gene regulation. This gene-centred atomistic view does not yield reliable criteria for homology, nor can it account convincingly for phenomena such as convergence and cooption. To understand the logic behind this plasticity, attention should be shifted from variation of existing characters to the preconditions for homology. This could be done by identifying the basic modules and their molecular regulation within the context of the most general, shared embryonic morphology. Mapping divergent embryonic trajectories onto different fates of these modules may allow us to throw light on the constrained sets of different, but related morphologies which can arise from different combinations of modules.
6.1 Introduction During the past two centuries the relationships between ontogeny and phylogeny have been the subject of extensive research and speculation. The most famous outcome of this intellectual enterprise is probably the fundamental biogenetic law (Haeckel 1866, 1874a), which claims that ontogeny recapitulates phylogeny and Animalia originated from an ancestor that was comparable to a gastrula formed by invagination of a hollow blastula. Its enduring popularity notwithstanding, the biogenetic law has always been controversial and at present seems to be definitely discredited (Richardson et al. 1997), yet, in recent times, the monophyly of Animalia has received consistent support from biomolecular studies showing unexpected M. Raineri Department of Biology, University of Genoa, Viale Benedetto XV 5, 16132 Genoa, Italy [email protected] P. Pontarotti (ed.), Evolutionary Biology from Concept to Application, c Springer-Verlag Berlin Heidelberg 2008
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conservation of the genetic networks from cnidarians to man (Conway Morris 2000, 2003; Erwin and Davidson 2002). The challenge of reconciling this molecular similarity with the amazing variation of biological forms has contributed to renewed interest in evolutionary developmental biology (EvoDevo). In spite of the benefits of unprecedented technical facilities, current attempts to elaborate an integrating theory linking developmental to evolutionary changes are thwarted by historically determined conceptual shortcomings. The present chapter analyses a few of these difficulties in order to suggest an alternative approach to the problem.
6.2 Two Different Approaches to Development and Evolution Being regained under the influence of the neoDarwinian synthesis, the new alliance between ontogeny and phylogeny considers evolutionary changes to be dependent on selection acting on genetic changes. The promotion of this concept in the majority of the current literature has relegated so
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