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George Gaylord Simpson: Biography, Discoveries & Evolution Theory

Instructor: Rachel Tustin

Dr. Rachel Tustin has a PhD in Education focusing on Educational Technology, a Masters in English, and a BS in Marine Science. She has taught in K-12 for more than 15 years, and higher education for ten years.

George Gaylord Simpson was a scientist who made lasting contributions to numerous fields of study. However, it is the ideas resulting from his work as a geologist and paleontologist that drive the field of evolution to this day.

In the Beginning…

George Gaylord Simpson was a frail and small child growing up with his family in Denver, Colorado. He was plagued by persistent ailments during his childhood and throughout his life, so as a child he accepted the title of ''smart but eccentric'' from his peers. However, he enjoyed mountain hikes and camping with his father in the Rocky Mountains, which lead to his natural comfort with geology and the great outdoors as an adult. Those experiences would also help him become an expert field geologist and paleontologist.

An image from the thesis American Mesozoic Mammalia, by Simpson
fossils

From 1918-1922 Simpson studied at the University of Colorado, Boulder. One of his early professors was Arthur J. Tieje, who encouraged Simpson's passion for geology and paleontology. However, Simpson never graduated from the university. In 1923, after four years, he left Colorado to complete his senior year at Yale University. He remained at Yale, earning a Ph.D. in geology in 1926. At the time he graduated, he was married to Lydia Petroja, with whom he would eventually have four daughters.

Simpson and Evolution

In 1927, Simpson became an assistant curator at the American Museum of Natural History. While working there, he had the unique opportunity to serve as a professor at Columbia University. Unlike his fellow paleontologists at the time, Simpson recognized the role of genetics in evolutionary theory. In his work Tempo and Mode in Evolution he proved, to the satisfaction of many, that the data emerging from genetics, evolution, and paleontology were compatible and in many ways supported each other.

The American Museum of Natural History
Americanmuseum

The work Tempo and Mode in Evolution made several arguments about evolution, including an idea known as quantum evolution, which Simpson used to explain the rapid evolution of species under certain circumstances. He also argued that multiple tempos of evolution can be seen in the fossil record, from bradytelic (slow tempo) to horotelic (medium tempo), and even tachytelic (rapid tempo). Simpson argued that these rates of evolution were the result of genetic change in populations. He argued that there were various determinants of the rate of evolution, such as rate and effect of mutations, population size, generation length, and natural selection. These ideas have persisted through evolutionary theory to this day. They include, for example, the notion that mutations with small effects are more likely to occur than a mutation that would cause a dramatic effect on a given species population.

After World War II, Simpson would espouse another theory known as the Synthetic Theory of Evolution. This theory further merged the ideas of evolution and genetics, and it is this theory that continues to be improved upon to this day. Today we know it as Neo-Darwinism. Synthetic Theory merged Darwin's ideas with modern concepts and mechanisms in genetics through studies of population dynamics.

This theory, supported by Simpson, applied more detailed concepts in genetics to evolution. For example, it takes into account how the process of Meiosis creates genetic variations by regrouping genes. It also considers the role of isolation, which is important in evolution. In isolation, populations get segregated into smaller populations due to geographical isolation caused by processes such as mountain building or seafloor spreading. The small population causes gene pairs over time to become homozygous, and the disadvantageous gene pairs will naturally weed out certain individuals in the population, leaving on the advantageous gene pairs in the surviving population.

Evolutionary Ideas and Penguin Tales

In the 1930's, when money was tight, Simpson would organize what were called the Scarritt Expeditions, which were funded by Horace Scarritt to look for mammal fossils in the Patagonian region of Argentina. In that region, the Chubut River in Argentina meets the Atlantic and forms an estuary. That particular estuary holds a massive collection of fossils. On an expedition there in 1933, Simpson happened across hundreds of penguin fossils. Being a paleontologist, he couldn't just leave them behind. There was one fossil in particular, though, that would make Simpson famous. It was a nearly intact penguin fossil, complete with a skull, that was on the scale of the King Penguin and was between 20 and 25 million years old.

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