Embryo Project Encyclopedia

Stephen Jay Gould studied snail fossils and worked at Harvard University in Cambridge, Massachusetts during the latter half of the twentieth century. He contributed to philosophical, historical, and scientific ideas in paleontology, evolutionary theory, and developmental biology. Gould, with Niles Eldredge, proposed the theory of punctuated equilibrium, a view of evolution by which species undergo long periods of stasis followed by rapid changes over relatively short periods instead of continually accumulating slow changes over millions of years. In his 1977 book, Ontogeny and Phylogeny, Gould reconstructed a history of developmental biology and stressed the importance of development to evolutionary biology. In a 1979 paper coauthored with Richard Lewontin, Gould and Lewonitn criticized many evolutionary bioligists for relying solely on adaptive evolution as an explanation for morphological change, and for failing to consider other explanations, such as developmental constraints.

David Starr Jordan studied fish and promoted eugenics in the US during the late nineteenth and early twentieth centuries. In his work, he embraced Charles Darwin s theory of evolution and described the importance of embryology in tracing phylogenic relationships. In 1891, he became the president of Stanford University in Stanford, California. Jordan condemned war and promoted conservationist causes for the California wilderness, and he advocated for the eugenic sterilization of thousands of Americans. Like many American eugenicists of the early twentieth century, Jordan combined ideas of Mendelian genetics and of Darwinian natural selection to form a basis for limiting or encouraging reproduction in certain individuals and groups based on their perceived hereditary fitness. Like other eugenicists, Jordan s attempt to control the reproductive fate of entire populations marked an episode in the history of reproduction and biology in which its concepts increasingly influenced the social and cultural contexts.

Georges Cuvier, baptized Georges Jean-Leopold Nicolas-Frederic Cuvier, was a professor of anatomy at the National Museum of Natural History in Paris, France, through the late eighteenth and early nineteenth centuries. Scholars recognize Cuvier as a founder of modern comparative anatomy, and as an important contributor to vertebrate paleontology and geology. Cuvier studied the form and function of animal anatomy, writing four volumes on quadruped fossils and co-writing eleven volumes on the natural history of fish with Achille Valenciennes. Moreover, Cuvier constructed a system of classification based on specific and well-articulated principles to help anatomists classify animal taxa. Cuvier had public debate in 1830 with Etienne Geoffroy Saint-Hilaire, a dispute centered on whether form or function matters most for the study of anatomy and whether the transmutation of organic forms can occur over time. Cuvier's opinions influenced the development of biology in France, and his arguments against transmutation of types influenced the reception of Charles Darwin's theory of evolution by natural selection among many French naturalists.

Etienne Geoffroy Saint-Hilaire, commonly known as Geoffroy, studied animals, their anatomy and their embryos, and teratogens at the National Museum of Natural History in Paris, France in the eighteenth and nineteenth centuries. Geoffroy also helped develop several specialized fields in the life sciences, including experimental embryology. In his efforts to experimentally demonstrate the theory of recapitulation, Geoffroy developed techniques to intervene in the growth of embryos to see whether they would develop into different kinds of organisms. Moreover, Geoffroy emphasized the concept of l'unite de composition (the unity of plan). Geoffroy disputed in 1830 with Georges Cuvier over whether form or function matters most for the study of anatomy and whether the transformation of organic forms can occur over time. Geoffroy's conceptual contributions, as well as his experimental research, influenced embryological research on animal morphology and teratogens, and later the field of evolutionary paleontology.

In his essay Evolution and Tinkering, published in
Science in 1977, Francois Jacob argued that a common analogy
between the process of evolution by natural selection and the
methods of engineering is problematic. Instead, he proposed to
describe the process of evolution with the concept of
bricolage (tinkering). In this essay, Jacob did not deny the
importance of the mechanism of natural selection in shaping complex
adaptations. Instead, he maintained that the cumulative effects of
history on the evolution of life, made evident by molecular data,
provides an alternative account of the patterns depicting the
history of life on earth. Jacob's essay contributed to
genetic research in the late twentieth century that emphasized
certain types of topics in evolutionary and developmental biology,
such as genetic regulation, gene duplication events, and the genetic
program of embryonic development. It also proposed why, in future
research, biologists should expect to discover an underlying
similarity in the molecular structure of genomes, and that they
should expect to find many imperfections in evolutionary history
despite the influence of natural selection.

In 2008 researchers Daniel Warner and Richard Shine tested the Charnov-Bull model by conducting experiments on the Jacky dragon (Amphibolurus muricatus), in Australia. Their results showed that temperature-dependent sex determination(TSD) evolved in this species as an adaptation to fluctuating environmental temperatures. The Charnov-Bull model, proposed by Eric Charnov and James Bull in 1977, described the evolution of TSD, although the model was, for many years, untested. Many reptiles and some fish exhibit non-genetic sex determination, in which an embryos' environment can influence the sex of the adult organism. Environmental conditions such as humidity or population density can alter sex in some organisms, and a widespread form of non-genetic sex determination is temperature-dependent sex determination. TSD reveals how embryonic development can contribute to the evolution of physiological processes. Researchers have documented TSD in a wide range of species, and they continue to investigate how such a sex determining system has evolved.