Teaching Evolution: George Gaylord Simpson: The major features of evolution

by Greg Mayer

Our third installment of Teaching Evolution is a paper by George Gaylord Simpson, the most influential paleontological contributor to the Modern Synthesis, and one of its key figures. In this paper, Simpson discusses a wide variety of phenomena revealed in the fossil record– parallelism, mosaic evolution, convergence, adaptation, conservatism, variation of evolutionary rates over time, variation of evolutionary rates among taxa, and variation of evolutionary rates among characters, to name a few– as exemplified by a group of South American hoofed mammals, the Notoungulata. The paper analyses these subjects in the context of an earlier discussion of variation and evolution in wasps by Alfred C. Kinsey, in which Simpson finds much to admire:

Kinsey’s review of this subject is the most recent and in many respects the most complete, and it is based on a remarkably thorough and profound study, of an exceptionally large mass of data.

Kinsey was later a famed sex researcher, and few are aware that he originally made his name as an entomologist studying wasps. Besides Simpson, Theodosius Dobzhansky, Ernst Mayr, and Julian Huxley– all influential contributors to the Synthesis– cited Kinsey’s work approvingly. (And Mayr, as he told me himself years later in a conversation in which he related Kinsey’s interviewing methods, was one of Kinsey’s subjects for his first studies of human sexual behavior!)

George Gaylord Simpson (1902-1984) was an American paleomammalogist and one of the crowning figures of the Modern Synthesis. In Tempo and Mode in Evolution (1944), Simpson showed that the patterns and rates of evolution and variation revealed in the fossil record are consistent with the mechanisms of inheritance and evolution that had been elucidated by geneticists and systematists in studies of extant taxa. In particular, Simpson argued that the distinction between microevolution and macroevolution was purely one of scale, and not one of evolutionary process. Educated at the University of Colorado and Yale, he spent his career at the American Museum of Natural History, the Museum of Comparative Zoology, and the University of Arizona. His books include The Meaning of Evolution (1949, revised 1967), The Major Features of Evolution (1953, a major reworking and updating of the themes of Tempo and Mode), Principles of Animal Taxonomy (1961), This View of Life (1964, a collection of popular articles) and The Geography of Evolution: Collected Essays (1965). His life and work are treated in his autobiography Concession to the Improbable (1978) and Leo Laporte’s George Gaylord Simpson: Paleontologist and Evolutionist (2000).

Simpson, G. G. 1937. Supra-specific variation in nature and in classification from the view-point of paleontology. American Naturalist 71 (734):236-267. (This link will allow you to read it online with a JSTOR account (which is free to anyone).)

Study Questions:
1. Simpson argues that evolutionary rates vary within the Notoungulata. What evidence does he use?

2. To what other group of mammals do the notohippids show parallel evolution? Why does Simpson think the characters undergoing parallel evolution are adaptive?

3.What does the variability of Henricosbornia reveal about the relationship between infraspecific and supraspecific variation?

4. What do the terms “habitus” and “heritage” mean? What does Simpson do with these concepts?

[The other installments of Teaching Evolution can be found by clicking ‘MOOC’ under “filed under” or “tags” just below.]


  1. ThyroidPlanet
    Posted April 12, 2018 at 11:22 am | Permalink


  2. busterggi
    Posted April 12, 2018 at 11:48 am | Permalink

    If evolution is real and grad students exist then why are there still kindergarteners?

  3. Steve Gerrard
    Posted April 12, 2018 at 11:55 am | Permalink

    I have and read a copy of The Meaning of Evolution, 1949 edition, from my father. What is amazing is how much of evolution was worked out, and how many big questions were answered, before DNA entered the picture.

  4. Posted April 12, 2018 at 12:02 pm | Permalink

    I know I should not be amazed at the care and detail of research done by older researchers, but I am still amazed anyway.

  5. Posted April 12, 2018 at 1:01 pm | Permalink

    I am really enjoying this Teaching Evolution series.
    Thank you for the link to the 1937 GGS paper. Embarrassed to say I cannot remember having read it. Seems like it should have been in the reading list for some of the grad seminar courses I took decades ago. (I did read The Meaning of Evolution and The Major Features of Evolution.)

  6. Posted April 12, 2018 at 2:11 pm | Permalink

    Someone gave me a copy of Simpson’s autobiography. It was disappointing. He told a lot of field stories of the conditions-were-exceptionally-difficult sort, but said little about his work on the evolutionary synthesis. Perhaps he feared that readers would be bored and consider it uninteresting.

    He really was one of the best thinkers among those (Dobzhansky, Mayr, him, Huxley, and Stebbins) who applied the Modern Synthesis and explained it to biologists.

  7. grasshopper
    Posted April 12, 2018 at 5:42 pm | Permalink

    Further reading material by G.G. Simpson can be found online at the Internet Archive. Of particular interest to me is the paper “Miocene penguins from Victoria, Australia, and Chubut, Argentina”, and his posthumously published sci-fi novel “The Dechronization Of Sam Magruder”.

  8. Angel
    Posted April 12, 2018 at 6:41 pm | Permalink

    Great! I wish more artículos are posted on Sciencw, as I am eLearning a lo4, and less on politically divisive topics

  9. colnago80
    Posted April 13, 2018 at 8:41 am | Permalink

    It should be pointed out that Simpson rejected the theory of Continental Drift and also characterized studies of exobiology as a science without a subject.

    • Posted April 13, 2018 at 9:44 am | Permalink

      Simpson rejected continental drift until the 1970s, but then accepted it as the geophysical data came in supporting it: see, for example, his Fossils and the History of Life (1983). One of the main reasons he rejected drift is that its early 20th century proponents thought that drift was a key feature of Cenozoic history (including very recently), and thus would have great implications for mammalian distribution (mammals having diversified primarily in the Cenozoic). But, it turns out that early drift proponents were largely wrong on this point, and drift has had mostly incremental effects on the positioning of continents and dispersal pathways during most of the Cenozoic. For example, we now understand the Panama land bridge as the result of plate tectonic forces, but the emergence of land bridges such as the Panamanian was also a feature of pre-drift geology, and thus nothing new to Simpson. While getting the geology right has been crucially important for understanding Earth history, relatively little has had to change about our understanding of mammalian distribution due to the acceptance of drift.

      It is true that, since there is no known extraterrestrial life, exobiology lacks a subject matter, and is pursued entirely by the invocation of analogies.


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