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Sandbox test area for Evolutionary developmental biology

Evolutionary developmental biology (informally called evo-devo) is a modern extension of comparative embryology, which compares the developmental processes of different organisms to determine the ancestral relationship between them, and to discover how developmental processes evolved. Like comparative embryology, evo-devo studies address 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. . Evo-devo studies are thus continuing to study the relationship between ontogeny and phylogeny that began in the nineteenth century.

The contemporary field of evo-devo gained impetus from two complementary discoveries. The first discovery is that much of morphological diversity in animals occurs despite the functional conservation of developmental genes, which are referred to as. These genes tend to be animal-specific and correspond largely to signaling proteins, transcription factors, and structural genes underlying epithelia] and or morphogenetic movements such as [[epithelial-mesenchymal transitions and cell migration. The toolkit metaphor is in reference to the capacity of evolutionary selection to use the same tools to build different body plans.  Work on the embryonic development of several model organisms, including the fly, nematode, fish, frog, and mouse, has tested the general applicability of these systems. These model systems have also allowed this principle to be tested using genes cloned from more distantly related animals such as cnidarians. The second discovery is that the evolution of morphological diversity can be explained by genetic changes in the gene regulatory sequences controlling the highly conserved gene regulatory toolkit. Thus, this second discovery solves the potential paradox raised by a highly conserved toolkit. For this reason, modern evo-devo studies prioritize the evolution of gene regulatory studies. Thus, a third development corresponding to whole genome sequencing and genomic methods has also facilitated the modern emergence and power of evo-devo studies.

The morphological diversity of land plants have also been found to based on a plant-specific developmental gene tool kit, although much less work has been done on plant gene regulatory sequences compared to animal evo-devo studies. Nonetheless, plant multicellularity has provided an independent case study for comparison to the evolutionary diversification of animal multicellularity.

Evo-devo studies have shown that just as evolution tends to create new genes from parts of old genes (molecular economy), 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.