George Gaylord Simpson (1902-1984) was an American palaeontologist. He published extensively on the taxonomy of extinct and extant animal species, the intercontinental migration of animals, and helped to reconcile the fields of palaeontology and genetics.
One of Simpson’s greatest contributions to evolutionary studies was as one of the founding fathers of the ‘modern synthesis’. In the early twentieth century the study of evolution experienced a renaissance with the work of Gregor Mendel. Even so, some considered that Mendel’s law of genetic inheritance was irreconcilable with the Darwinian theory of evolution. That is, evolution by natural selection asserted that new traits can appear in a species that were not previously present. This conflicted with Mendelian genetics which stated that genes – although passed on to offspring in different combinations – remained unchanged through the generations.
However, in the early 20th century, an increasing amount of research was carried out on how genes ‘mutate’. Mutation creates permanent changes to genes and can lead to new traits in a given species which have never previously been seen; totally harmonious with evolution by natural selection. The modern synthesis argued that Darwin’s theory and Mendel’s Law were complimentary pieces of the same jigsaw puzzle. It stressed that whilst Darwinian evolution identified the importance of natural selection in evolution, changes in the gene pool are also caused by genetic drift, mutation and gene flow.
Simpson was especially keen to integrate the fields of palaeontology and genetics, and this was elegantly demonstrated in his 1944 publication Tempo and Mode in Evolution. He used palaeontology to show that evolution was not ‘goal-oriented’ (as was being argued at the time by those who thought Darwinian theory could not be reconciled with Mendelian inheritance). In particular, he used the evolutionary history of the horse to show that evolution is not a straightforward, linear process, but one that is littered with extinctions. Broadly speaking, the modern synthesis shows how different academic disciplines – in this case, initially palaeontology and genetics – come together to answer scientific questions common to them both. As the decades have passed, academia in general and evolutionary studies in particular, have become increasingly multi-disciplinary; it takes information from a broad range of disciplines to build a thorough understanding of the evolutionary process.
Simpson can also be noted for his forceful opposition to Alfred Wegener’s theory of Continental Drift. Continental drift – which, in the form of plate tectonics, is now an accepted fact –is the idea that the Earth’s continents have moved over millions of years. This in turn explains why we find very similar fossils on continents that are today separated by vast oceans. Simpson however, argued that the continents were fixed, arguing that the distribution of extinct creatures could be explained by processes other than moving landmasses. Such was the respect for Simpson, together with the influence of his publications that this led to the theory of Continental Drift losing credibility in the scientific world.
However, by the 1960’s geophysical evidence began to support – and ultimately validated – Wegener’s theory of Continental Drift, and this in turn prompted Simpson to revise his stance. In doing so, Simpson demonstrated what the scientific method is all about; testing a hypothesis, holding it up to scrutiny and, if need be, revising one’s own theory in the face of overwhelming facts. As a point of interest, it should be noted that Simpson’s idea of continental immobility, although wrong in the broad sense, had several fruitful aspects, such as the idea of “island hopping”, “rafting” and that Antarctica once served as a land corridor from South America to Australia. So too our understanding of the evolution of South America’s biotas very largely hinges on first its isolation, with occasional episodes of rafting from Africa, before connectivity was made via the Isthmus of Panama, first as island hopping and then a corridor. Animals moved in either direction and that explains why we see opposums in Toronto and llamas in Chile.
Text copyright © 2015 Victoria Ling. All rights reserved.
Eldredge, N. (1985) Unfinished Synthesis: Biological Hierarchies and Modern Evolutionary Thought. Oxford University Press.
Frankel, H. (1987) The continental drift debate. In Scientific Controversies: Case Studies in the Resolution and Closure of Disputes in Science and Technology (H.T. Engelhardt Jr and A.L. Caplan, eds), pp. 203-248. Cambridge University Press.
Laporte, L.O.F. (1994) Simpson on species. Journal of the History of Biology 27, 141–159.
Olson, E.C. (1991) George Gaylord Simpson. 1902-1984. A biographical memoir by Everett Olson. Biographical Memoirs of the National Academy of Sciences 60, 331–353.
Simpson, G.G. (1943) Mammals and the nature of continents. American Journal of Science 241, 1-31.
Simpson, G.G. (1944) Tempo and Mode in Evolution. Columbia University Press.