Evolutionary developmental biology
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Evolutionary developmental biology (evolution of development or informally, evo-devo) is a field of evolved. It addresses the origin and evolution of embryonic development; how modifications of development and developmental processes lead to the production of novel features, such as the evolution of feathers; the role of developmental plasticity in evolution; how ecology impacts development and evolutionary change; and the developmental basis of homoplasy and homology.
Although interest in the relationship between shape and form.
Nevertheless, it now appears that just as evolution tends to create new genes from parts of old genes (molecular economy), evo-devo demonstrates that evolution alters developmental processes to create new and novel structures from the old gene networks (such as bone structures of the jaw deviating to the ossicles of the middle ear) or will conserve (molecular economy) a similar program in a host of organisms such as eye development genes in molluscs, insects, and vertebrates.  Initially the major interest has been in the evidence of homology in the cellular and molecular mechanisms that regulate body plan and organ development. However subsequent approaches include developmental changes associated with speciation.
- Basic principles 1
- History 2
- The developmental-genetic toolkit 3
- Development and the origin of novelty 4
- See also 5
- Sources 6.1
- Further reading 7
- External links 8
developmental mechanisms began to form.
Currently, it is well understood how genetic mutation occurs. However, developmental mechanisms are not understood sufficiently to explain which kinds of phenotypic variation can arise in each generation from variation at the genetic level. Evolutionary developmental biology studies how the dynamics of development determine the phenotypic variation arising from genetic variation and how that affects phenotypic evolution (especially its direction). At the same time evolutionary developmental biology also studies how development itself evolves.
Thus the origins of evolutionary developmental biology come both from an improvement in molecular biology techniques as applied to development, and from the full appreciation of the limitations of classic neo-Darwinism as applied to phenotypic evolution. Some evo-devo researchers see themselves as extending and enhancing the modern synthesis by incorporating into it findings of molecular genetics and developmental biology.
Evolutionary developmental biology is not yet as of 2014 a unified discipline, but can be distinguished from earlier approaches to evolutionary theory by its focus on a few crucial ideas. One of these is modularity: as has been long recognized, plants and animal bodies are modular: they are organized into developmentally and anatomically distinct parts. Often these parts are repeated, such as fingers, ribs, and body segments. Evo-devo seeks the genetic and evolutionary basis for the division of the embryo into distinct modules, and for the partly independent development of such modules.
Another central idea recognizes that some embryogenesis (e.g., the genes of the "developmental-genetic toolkit", see below), just regulating them differently.
Similarly, promoter regions of genes, those DNA sequences at which the products of some genes bind to and control the activity of the same or other genes, not only protein-specifying sequences. This finding suggested that the crucial distinction between different species (even different orders or phyla) may be due less to differences in their content of gene products than to differences in spatial and temporal expression of conserved genes. The implication that large evolutionary changes in body morphology are associated with changes in gene regulation, rather than with the evolution of new genes, suggested that Hox and other "switch" genes may play a major role in evolution, something that contradicts the neo-Darwinian synthesis.
Another focus of evo-devo is phenotypes are not uniquely determined by their genotypes. If generation of phenotypes is conditional, and dependent on external or environmental inputs, evolution can proceed by a "phenotype-first" route, with genetic change following, rather than initiating, the formation of morphological and other phenotypic novelties. Mary Jane West-Eberhard argued the case for this in her 2003 book Developmental plasticity and evolution.
An early version of Edinburgh and London schools of higher anatomy around 1830, notably by Robert Edmond Grant, but was opposed by Karl Ernst von Baer's embryology of divergence in which embryonic parallels only applied to early stages where the embryo took a general form, after which more specialised forms diverged from this shared unity in a branching pattern. The anatomist Richard Owen used this to support his idealist concept of species as showing the unrolling of a divine plan from an archetype, and in the 1830s attacked the transmutation of species proposed by Lamarck, Geoffroy and Grant. In the 1850s Owen began to support an evolutionary view that the history of life was the gradual unfolding of a teleological divine plan, in a continuous "ordained becoming", with new species appearing by natural birth.In On the Origin of Species (1859), Charles Darwin proposed evolution through natural selection, a theory central to modern biology. Darwin recognised the importance of embryonic development in the understanding of evolution, and the way in which von Baer's branching pattern matched his own idea of descent with modification:
|“||We can see why characters derived from the embryo should be of equal importance with those derived from the adult, for a natural classification of course includes all ages.||”|
Ernst Haeckel (1866), in his endeavour to produce a synthesis of Darwin's theory with Lamarckism and Naturphilosophie, proposed that "ontogeny recapitulates phylogeny," that is, the development of the embryo of every species (ontogeny) fully repeats the evolutionary development of that species (phylogeny), in Geoffroy's linear model rather than Darwin's idea of branching evolution. Haeckel's concept explained, for example, why humans, and indeed all vertebrates, have gill slits and tails early in embryonic development. His theory has since been discredited. However, it served as a backdrop for a renewed interest in the evolution of development after the modern evolutionary synthesis was established (roughly 1936 to 1947).
Stephen Jay Gould called this approach to explaining evolution as terminal addition; as if every evolutionary advance was added as new stage by reducing the duration of the older stages. The idea was based on observations of neoteny. This was extended by the more general idea of heterochrony (changes in timing of development) as a mechanism for evolutionary change.
D'Arcy Thompson postulated that differential growth rates could produce variations in form in his 1917 book On Growth and Form. He showed the underlying similarities in body plans and how geometric transformations could be used to explain the variations.
Edward B. Lewis discovered homeotic genes, rooting the emerging discipline of evo-devo in molecular genetics. In 2000, a special section of the Proceedings of the National Academy of Sciences (PNAS) was devoted to "evo-devo", and an entire 2005 issue of the Journal of Experimental Zoology Part B: Molecular and Developmental Evolution was devoted to the key evo-devo topics of evolutionary innovation and morphological novelty.
John R. Horner began his project "How to Build a Dinosaur" in 2009 in conjunction with his published book of the same name. Using the principles and theories of evolutionary developmental biology, he took a chick embryo and attempted to change the development so it grew components similar to a dinosaur. He successfully grew buds of teeth, and is currently continuing work on growing a tail, and changing the wings to claws. Horner used evolutionary developmental biology on a chick embryo because he knew he couldn't make an exact replica of a dinosaur since there is no more DNA so instead he just took the framework still in the chick's DNA that allowed it to evolve from a dinosaur.
The developmental-genetic toolkit
The developmental-genetic toolkit consists of a small fraction of the genes in an organism's genome whose products control its development. These genes are highly conserved among Hox genes, transcription factors containing the more broadly distributed homeobox protein-binding DNA motif, function in patterning the body axis. Thus, by combinatorial specifying the identity of particular body regions, Hox genes determine where limbs and other body segments will grow in a developing embryo or larva. A paragon of a toolbox gene is Pax6/eyeless, which controls eye formation in all animals. It has been found to produce eyes in mice and Drosophila, even if mouse Pax6/eyeless was expressed in Drosophila.
This means that a big part of the morphological evolution undergone by organisms is a product of variation in the genetic toolkit, either by the genes changing their expression pattern or acquiring new functions. A good example of the first is the enlargement of the beak in Darwin's Large Ground-finch (Geospiza magnirostris), in which the gene BMP is responsible for the larger beak of this bird, relative to the other finches.
The loss of legs in snakes and other squamates is another good example of genes changing their expression pattern. In this case the gene Distal-less is very under-expressed, or not expressed at all, in the regions where limbs would form in other tetrapods. This same gene determines the spot pattern in butterfly wings, which shows that the toolbox genes can change their function.
Toolbox genes, as well as being highly conserved, also tend to evolve the same function convergently or in parallel. Classic examples of this are the already mentioned Distal-less gene, which is responsible for appendage formation in both tetrapods and insects, or, at a finer scale, the generation of wing patterns in the butterflies Heliconius erato and Heliconius melpomene. These butterflies are Müllerian mimics whose coloration pattern arose in different evolutionary events, but is controlled by the same genes. The previous supports Kirschner and Gerhart's theory of Facilitated Variation, which states that morphological evolutionary novelty is generated by regulatory changes in various members of a large set of conserved mechanisms of development and physiology.
Development and the origin of novelty
Among the more surprising and, perhaps, counterintuitive (from a phyla are not necessarily reflected in diversity at the level of the sequences of genes, including those of the developmental genetic toolkit and other genes involved in development. Indeed, as Gerhart and Kirschner have noted, there is an apparent paradox: "where we most expect to find variation, we find conservation, a lack of change".
Even within a species, the occurrence of novel forms within a population does not generally correlate with levels of genetic variation sufficient to account for all morphological diversity. For example, there is significant variation in limb morphologies amongst salamanders and in differences in segment number in centipedes, even when the respective genetic variation is low.
A major question then, for evo-devo studies, is: If the morphological novelty we observe at the level of different gene regulation are "second-order" effects of genes, resulting from the interaction and timing of activity of gene networks, as distinct from the functioning of the individual genes in the network.
The discovery of the homeotic Hox gene family in vertebrates in the 1980s allowed researchers in developmental biology to empirically assess the relative roles of gene duplication and gene regulation with respect to their importance in the evolution of morphological diversity. Several biologists, including Sean B. Carroll of the University of Wisconsin–Madison suggest that "changes in the cis-regulatory systems of genes" are more significant than "changes in gene number or protein function". These researchers argue that the combinatorial nature of transcriptional regulation allows a rich substrate for morphological diversity, since variations in the level, pattern, or timing of gene expression may provide more variation for natural selection to act upon than changes in the gene product alone.
- Animal evolution
- Baldwin effect
- Body plan
- Cell signaling
- Cell signaling networks
- Developmental biology
- Developmental systems theory
- Evolution & Development (journal)
- Evolution of multicellularity
- Gene regulatory network
- Genetic assimilation
- List of gene families
- Ontogeny recapitulates phylogeny
- Evolutionary history of plants
- Promoter (biology)
- Signal transduction
- Transcription factor
- Prum, R.O., Brush, A.H. (March 2003). "Which Came First, the Feather or the Bird?".
- Hall, Brian K. (2000). "Evo-devo or devo-evo—does it matter". Evolution & Development 2 (4): 177–178.
- Palmer, RA (2004). "Symmetry breaking and the evolution of development".
- Tomarev, Stanislav I.; Callaerts, Patrick; Kos, Lidia; Zinovieva, Rina; Halder, Georg; Gehring, Walter; Piatigorsky, Joram (1997). "Squid Pax-6 and eye development". Proceedings of the National Academy of Sciences 94 (6): 2421–2426.
- Pichaud, Franck; Desplan, Claude (August 2002). "Pax genes and eye organogenesis". Current Opinion in Genetics & Development 12 (4): 430–434.
- Pennisi, E (2002). "EVOLUTIONARY BIOLOGY:Evo-Devo Enthusiasts Get Down to Details". Science 298 (5595): 953–955.
- Monod, J; Changeux, JP; Jacob, F (1963). "Allosteric proteins and cellular control systems". Journal of Molecular Biology 6 (4): 306–329.
- West-Eberhard, M-J. (2003). Developmental plasticity and evolution. New York: Oxford University Press.
Desmond 1989, pp. 53–53, 86–88, 337–340
Secord 2003, pp. 252–253
Bowler 2003, pp. 120–128, 208
Secord 2003, pp. 424, 512
- Desmond & Moore 1991, pp. 490–491
- Bowler 2003, pp. 170, 190–191
- Ridley, Mark (2003). Evolution. Wiley-Blackwell.
- Goodman CS and Coughlin BS (Eds). (2000). "Special feature: The evolution of evo-devo biology".
- Jack Horner, James Gorman. (2009). "Jack Horner's Plan to Bring Back Dinosaurs"
- Thomas Hayden. (26 September 2011). "How to Hatch a Dinosaur". Wired
- Xu, P.X., Woo, I., Her, H., Beier, D.R., Maas, R.L. (1997). "Mouse Eya homologues of the Drosophila eyes absent gene require Pax6 for expression in lens and nasal placode". Development 124 (1): 219–231.
- Abzhanov, A.; Protas, M.; Grant, B.R.; Grant, P.R.; Tabin, C.J. (2004). "Bmp4 and Morphological Variation of Beaks in Darwin's Finches". Science 305 (5689): 1462–1465.
- Cohn, M.J.; Tickle, C. (1999). "Developmental basis of limblessness and axial patterning in snakes". Nature 399 (6735): 474–479.
- Beldade, P.; Brakefield, P.M.; Long, A.D. (2002). "Contribution of Distal-less to quantitative variation in butterfly eyespots". Nature 415 (6869): 315–318.
- Baxter, S.W.; Papa, R.; Chamberlain, N.; Humphray, S.J.; Joron, M.; Morrison, C.; ffrench-Constant, R.H.; McMillan, W.O.; Jiggins, C.D. (2008). "Convergent Evolution in the Genetic Basis of Mullerian Mimicry in Heliconius Butterflies". Genetics 180 (3): 1567–1577.
- Gerhart, John; Kirschner, Marc (2007). "The theory of facilitated variation". Proceedings of the National Academy of Sciences 104 (suppl1): 8582–8589.
- Gerhart, John; Kirschner, Marc (1997). Cells, Embryos and Evolution. Blackwell Science.
- Carroll, Sean B.; Grenier, Jennifer K.; Weatherbee, Scott D. (2005). From DNA to Diversity: Molecular Genetics and the Evolution of Animal Design — Second Edition. Blackwell Publishing.
- Carroll, Sean B. (Jul 2008). "Evo-devo and an expanding evolutionary synthesis: a genetic theory of morphological evolution.". Cell 134 (1): 25–36.
- Carroll, Sean B. (2000). "Endless forms: the evolution of gene regulation and morphological diversity".
- Jablonka, Eva; Lamb, Marion (1995). Epigenetic Inheritance and Evolution: The Lamarckian Dimension. Oxford, New York: Oxford University Press.
- Müller, Gerd B. and Newman, Stuart A., ed. (2003).
- Bowler, Peter J. (2003). Evolution: the history of an idea. Berkeley: University of California Press.
- Desmond, Adrian J.; Moore, James William (1991). Darwin. London: Michael Joseph.
- Secord, James A. (2003). Victorian sensation: the extraordinary publication, reception, and secret authorship of Vestiges of the natural history of creation. Chicago: University of Chicago Press.
- Carroll, Sean B. (2005). Endless Forms Most Beautiful: The New Science of Evo Devo and the Making of the Animal Kingdom. Norton.
- Kirschner, Marc; Gerhart, John (2005). The Plausibility of Life: Resolving Darwin's Dilemma. Yale University Press.
- Laubichler, Manfred D. and Maienschein, Jane, ed. (2007). From Embryology to Evo-Devo: A History of Developmental Evolution.
- Orr, H. Allen (2005-10-24). "Turned on: A revolution in the field of evolution?". Discussion of Carroll, Endless Forms Most Beautiful
- Sommer, Ralf J. (2009). "The future of evo–devo: model systems and evolutionary theory". Nature Reviews Genetics 10 (6): 416–422.
- Scott F. Gilbert, The morphogenesis of evolutionary developmental biology
- Tardigrades (water bears) as evo-devo models, a short video from NPR's Science Friday