Darwinistas 'clamam' pela Síntese Evolutiva Ampliada para livrar Darwin de uma falência heurística

sexta-feira, junho 26, 2009

Extending the Evolutionary Synthesis

Gerd B. Müller

Department of Theoretical Biology, University of Vienna


Since the time of the last major conceptual integration in evolutionary biology, the Modern Synthesis of the 1930s and 1940s, the biosciences have made significant advances. The discovery of the DNA, the spread of molecular tools, the rise of high throughput technologies, the pervasive entry of computation, to name but a few, have led to fundamentally different kinds of data and models of biological processes. The theoretical framework of evolutionary biology, by contrast, has remained surprisingly constant over the same period of time. Or so it seems, because upon closer scrutiny it becomes evident that today's evolutionary biology operates with numerous concepts that were not part of the original Synthesis theory. Since their retrospective inclusion into the well defined classical framework is impossible, propositions for a new and expanded theoretical synthesis are on the rise (Carroll 2000; Love 2003; Kutschera and Niklas 2004; Müller 2007; Pigliucci 2007; Rose and Oakley 2007; Carroll 2008; Pigliucci and Müller 2009a). Whatever the specifics of its eventual structure, already now several characteristics by which an Extended Synthesis will reach beyond the confines of the traditional framework can be delineated.

For decades the classical approach has concentrated on population dynamics and speciation. The Modern Synthesis held that populations contain genetic variation caused by random mutation and recombination, and evolution occurs by changes in gene frequencies that are brought about by natural selection, genetic drift, and gene flow. Continued genetic variation results in small changes of quantitative traits, adaptive variants result in differential reproduction, reproductive isolation results in speciation. This theoretical framework has been highly successful in explaining gradual, adaptive, and selectional change in populations. On purpose it excluded modes and phenomena of evolution that did not square with these issues.

The new conceptual input comes from both traditional fields of evolutionary theory and from entirely new areas of evolutionary research. In the traditional fields the understanding of the modes of genetic variation, natural selection, inheritance, and adaptation has undergone considerable modification. Multilevel selection, gene network evolution, epigenetic inheritance, niche inheritance, replicator concepts, among others, provide a more differentiated picture of the variational dynamics of population change. This, in itself, constitutes a major, in parts even iconoclastic theoretical advancement. Even more substantial amendments arise from those fields that address issues not formerly covered by the Synthesis framework, in particular the evolution of organismal complexity. Here belong the factors responsible for the origins of non-adaptive traits, structural innovations, homoplasy, organismal bodyplans, and other phenomena of phenotypic evolution.

Among the new fields, evolutionary developmental biology (EvoDevo) probably has the most far-reaching consequences. EvoDevo has become a highly productive discipline that has diversified into several branches of empirical research. The spectacular discoveries regarding, for instance, gene regulatory evolution, including its deep similarities in organisms that exhibit radically different architectures, have revolutionized our understanding of how development evolves. Less attention has been given to the important ways in which EvoDevo has informed evolutionary theory. Developmental constraint, facilitated variation, epigenetic innovation, dynamical patterning modules, to name but a few of the conceptual innovations provided by EvoDevo, all address problems of phenotypic evolution that were not accessible by the traditional focus on population dynamics. Together with concepts emerging from other new areas of research, such as phenotypic plasticity or evolvability, EvoDevo will contribute key components to any extended evolutionary synthesis.

A characteristic feature of these developments in evolutionary theory is the shift from a population dynamic emphasis favored by the Modern Synthesis towards a causal-mechanistic explanation of phenotypic complexity. The understanding of the evolution of dynamic organizing relations between genes, cells, and tissues, as well as the interactions of these processes with environmental conditions, will permit predictiveness not only about what is adaptively varied but also about what is possible to arise in organismal evolution. The resulting picture of an Extended Synthesis, however preliminary in its present outline, and despite being more advanced in molecular detail, will be less gene centred and more pluralistic than its classical predecessor. An extended framework expands the explanatory reach of evolutionary theory to non-gradual and non-adaptive phenomena of phenotypic evolution and entails a revised understanding of the causal roles of natural selection. More detailed treatments of the conceptual elements shaping the Extended Synthesis can be found in a forthcoming volume (Pigliucci and Müller 2009b).

Key references

Carroll RL (2000) Towards a new evolutionary synthesis. Trends in Ecology & Evolution 15: 27-32.

Carroll SB (2008) EvoDevo and an Expanding Evolutionary Synthesis: a genetic theory of morphological evolution. Cell 134: 25-36.

Kutschera U, Niklas KJ (2004) The modern theory of biological evolution: an expanded synthesis. Naturwissenschaften 91:255-276.

Love AC (2003) Evolutionary morphology, innovation, and the synthesis of evolutionary and developmental biology. Biology and Philosophy 18: 309-345.

Müller GB (2007) EvoDevo: extending the evolutionary synthesis. Nature Reviews Genetics 8: 943-949.

Pigliucci M (2007) Do we need an extended evolutionary synthesis? Evolution 61(12): 2743-2749.

Pigliucci M and GB Müller (2009a, in press) Elements of an extended evolutionary synthesis. In: Evolution: The Extended Synthesis. Pigliucci M and GB Müller eds. Cambridge: MIT Press.

Pigliucci M and GB Müller eds. (2009b, in press) Evolution: The Extended Synthesis. Cambridge: MIT Press.

Rose MR, Oakley TH (2007) The new biology: Beyond the Modern Synthesis. Biol Direct 2:30.