Embryology Today

The current field of evolutionary developmental biology (or "evo-devo") seeks to understand the evolution of embryonic development and how modifications in development can lead to the production of novel features.

Through advances in systematics, there is a better understanding of the evolutionary relationships between organisms. Within such a framework, evolutionary developmental biologists can now address questions about what developmental changes might be important to evolution and how those changes came about. This once seemed like a daunting task to the mid-twentieth-century embryologist, but recent advances in developmental biology have created exciting new avenues of research for those interested in understanding the developmental basis for life's diversity.

The modern-day unification of embryology and evolution can be traced back to the mid-1980s with the discovery of a group of developmental regulatory genes called Hox genes. Initially discovered in insects, Hox genes were subsequently discovered in every major animal group. These genes were found to be highly conserved in their DNA sequence, chromosomal structure, and function. For instance, when the DNA sequences of these genes were compared, they were found to be remarkably similar in distantly related animals. In insects and mammals, these genes were found to be linked in groups along chromosomes, and expressed sequentially along the developing embryo. In addition, in insects and mammals, the Hox genes were found to play similar roles in providing cues for the proper placement of organs in a developing embryo. The remarkable conservation in structure and function of the Hox genes makes them particularly interesting for comparing developmental programs across distantly related animal groups.

In addition to the Hox genes, other developmental regulatory genes and gene pathways have been found to be highly conserved. For example, genes that control the development of limbs in insects also regulate limb development in mammals. Insects and mammals also share the same genetic controls for the devel opment of eyes (see Homology and Embryology, above). From these discoveries, it appears that all of animal life shares a common developmental blueprint. Parallel discoveries have also been made in plant development. Genes that control how flowers develop are conserved across all of the flowering plants. These new insights into evolutionary developmental biology have revealed that the diversity of life evolved not so much from the evolution of new genes as from the application during development of ancestral genes in new ways.

—Paulyn Cartwight

See also: Evolution; Evolutionary Biodiversity; Evolutionary Genetics; Molecular Biology and Biodiversity; Zoology

Bibliography

Buss, Leo W. 1987. The Evolution of Individuality. Princeton: Princeton University Press; Gilbert, Scott F. 2000. Developmental Biology, 6th ed. Sunderland, MA: Sinauer; Gilbert, Scott F., and Anne M. Rau-nio, eds. 1997. Embryology: Constructing an Organism. Sunderland, MA: Sinauer; Gould, Stephen J. 1977. Ontogeny and Phylogeny. Cambridge: Harvard University Press; Hall, Brian K. 1992. Evolutionary Developmental Biology. London: Chapman and Hall; Raff, Rudolf A., and Thomas C. Kaufman. 1983. Embryos, Genes, and Evolution. New York: Macmillan

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