Teaching Evolution: Sewall Wright: Evolution in space

March 9, 2019 • 10:30 am

by Greg Mayer

Our next installment of Teaching Evolution for this spring concerns Sewall Wright. His contributions were wide-ranging, but he is most noted for his integration of population structure (population size, migration) and selection into what he called the “shifting balance” theory. In this theory, genetic drift, migration, and selection interact to produce what he saw as the most favorable conditions for evolutionary advance. The reading is a brief precis of his much longer 1931 paper in Genetics, but in many ways was more influential, as it exposed a wider audience to his ideas. Modern appreciations of the shifting balance theory are given by Nick Barton (2016) and Norm Johnson (2008).

Sewall Wright, with guinea pig.

Sewall Wright (1889-1988) was, along with R.A. Fisher and J.B.S. Haldane, one of the founders of theoretical population genetics, which synthesized Mendelian inheritance with Darwinian natural selection, thus laying the foundations of modern evolutionary biology. His classic paper “Evolution in Mendelian Populations” (Genetics, 1931) laid out his synthesis, and led to his election to the National Academy of Sciences while still a young man. Like Darwin, Wright studied carefully the work of animal breeders, and this strongly influenced his ideas on evolution, which he called the “shifting balance” theory. Although sometimes caricatured as a theory emphasizing random genetic drift, Wright stressed the importance of the interaction of drift, selection, and migration in adaptive evolution. Wright strongly influenced Dobzhansky, and he coauthored five papers in the latter’s “Genetics of Natural Populations” series. Beginning with his graduate studies at Harvard, Wright’s organism of choice for genetic studies throughout his career, which ended with a very productive 33 year retirement at the University of Wisconsin, was the guinea pig (note what is in his left hand in the photo). He is author of the monumental four volume Evolution and the Genetics of Populations (1968-1978). William Provine has edited a collection of Wright’s most important papers, Evolution: Selected Papers (1986), and written an insightful and analytic biography, Sewall Wright and Evolutionary Biology (1986).


Wright, S. 1932. The role of mutation, inbreeding, crossbreeding, and selection in evolution. Proceedings of the Sixth International Congress of Genetics 1:356-366.

Study Questions:

1. In this paper, Wright introduces the idea of a fitness surface or adaptive ‘landscape’ (see esp. Fig. 2). What do the x and y axes (the two dimensions of the ‘map’ on the paper) represent? What does the ‘altitude’ of a point on the landscape represent? What does a peak in the landscape represent? What does a valley in the landscape represent?

2. In one sentence in the first half of the paper, Wright succinctly states the Hardy-Weinberg equilibrium for allele frequencies, and its cause. Find and quote the sentence. Show that Wright understands the H-W principle.

3. Why is it difficult for a species to evolve across a valley from one peak to another if selection is the only evolutionary force? How does this lead Wright to argue for the importance of drift (inbreeding) and migration (crossbreeding), as well as selection, in allowing species to reach the highest adaptive peaks?


Jerry addendum:  While Wright’s theory was influential, and was incorporated by Theodosius Dobzhansky into his view of the Modern Evolutionary Synthesis (see his book Genetics and the Origin of Species), I find the theory deeply flawed. With two colleagues, Nick Barton and Michael Turelli, I wrote a long critique of that theory in 1997. Our paper was in turn criticized in two papers, one by Mike Wade and Charles Goodnight, and the other by Steven Peck et al.  We then rebutted these papers in another Evolution paper in 2000. All four references and links are below.

In my biased estimation, our critique did stem the tide of enthusiasm for Wright’s theory; in fact, Wright’s colleague James Crow at Madison said that our paper prompted him to stop accepting that theory. I’m not sure whether Greg mentions the critiques and attempted rebuttals in his lecture, but I’m putting them here for readers.

Coyne, J. A., N. H. Barton, and M. Turelli.  1997.  A critique of Sewall Wright’s shifting balance theory of evolution.  Evolution 51:643-671.

Wade, M. and C. J. Goodnight. 1998. The theories of Fisher and Wright in the context of metapopulations: when nature does many small experiments. Evolution 52:1537–1553.

Peck, S. L., S. P. Ellner, and F. Gould. 1998. A spatially explicit stochastic model demonstrates the feasibility of Wright’s shifting balance theory. Evolution 52:1834–1839.

Coyne, J. A., M. Turelli, and N. H. Barton.  2000.  Is Wright’s shifting balance process important in evolution? Evolution 54: 306-317.


Teaching Evolution: Theodosius Dobzhansky: Genetics of natural populations

February 27, 2019 • 10:30 am

by Greg Mayer

Readers may recall that last spring I began what Jerry called a “mini-MOOC” on evolutionary biology. Because I began making posts fairly late in the semester, I got to only seven installments before the semester ended. I’m teaching the same course, BIOS 314 Evolutionary Biology, this spring, and so I’d like to start up again.

In the class I have the students read a series of what I regard to be classic papers or extracts–—one each week—and these are what I want to share with WEIT readers. Each reading is accompanied by a brief biography and illustration of the author, and a small number of study questions, designed to guide the student in understanding the reading. I sometimes assign these questions as homework essays, or include them on exams. When possible, I will provide links to the readings. The installments so far have been Charles Darwin, A.W.F. Edwards, George Gaylord Simpson, Charles Lyell, Alfred Sherwood Romer, Alfred Russel Wallace, and Richard C. Lewontin. We pick up with Theodosius Dobzhansky. Dobzhansky was a key figure in the “Modern Synthesis” of evolutionary biology in the 20th century (as described below). Jerry had intended to do his doctoral work with “Doby” (as he was known later in his career; students from earlier knew him as “Dodik”), but wound up studying with Dick Lewontin, who had been a student of Doby’s, and thus Jerry is Doby’s academic grandchild.

Theodosius Dobzhansky (1900-1975) was a Russian-American geneticist who was arguably the most important evolutionary biologist of the 20th century. Completing (although never formally receiving) an undergraduate degree at the University of Kiev, he began his career conducting field studies of coccinellid beetles and laboratory experiments on Drosophila. In 1927 he received a fellowship to come to America and work with T. H. Morgan at his famed “fly room” at Columbia University. As a geneticist working at the epicenter of American genetics, Dobzhansky was well aware of the important empirical and theoretical advances being made in genetics; as a field worker and experimentalist, he was able to tie these developments more closely into the phenomena of natural populations. He synthesized the theoretical, experimental, and field approaches in his classic book Genetics and the Origin of Species (1937). It was through this book, much more so than through the previous synthetic, but more theoretical, works of Fisher, Haldane and Wright, that the biological community as a whole became aware of the developments in evolutionary biology, and the book inspired an outpouring of work carried on in the same synthetic spirit. Dobzhansky is well known for his two aphorisms, “Nothing in biology makes sense except in the light of evolution”, and “Heaven is where, when the experiment is over, you don’t need statistics to figure out what happened.” His major works include Genetics and the Origin of Species (3rd ed., 1951), Mankind Evolving (1962) and Genetics of the Evolutionary Process (1970). His monumental 43-paper series on the “Genetics of Natural Populations” (1938-1975) has been reprinted, with extensive historical and biographical commentary, as Dobzhansky’s Genetics of Natural Populations I-XLIII (1981), edited by Lewontin, Wallace, Moore, and Provine.

Dobzhansky, Th.1951. Genetics and the Origin of Species. 3rd ed. Columbia University Press, New York. Excerpts from Chap. III. “Mutation in Populations” (pp. 50-55, 70-75) and Chap. V. “Adaptive Polymorphism” (pp. 108-123, 129-134).

Study Questions:

1. What is blending, as opposed to particulate, inheritance? What are the consequences of the two sorts of inheritance for the evolutionary process? What analogy does Dobzhansky use to illustrate the effect of blending inheritance?

2. How does Dobzhansky see the “stored” genetically variability of natural populations and the generally deleterious nature of mutations nonetheless leading to populations being adapted to their conditions of existence?

3. Can a phylogeny be estimated for infraspecific variants? [We usually think of phylogeny being estimated for species, so that we can say, for example, lions and tigers share a more recent common ancestor than either does with the house cat. But could we construct a phylogeny for, say breeds of house cat? Or subspecies of tiger? Or mitochondrial haplotypes of the lion? See Dobzhansky’s Fig. 4 (p. 113 in the reading) for his answer.]

4. What is balanced polymorphism? How does balanced polymorphism relate genetic variability and natural selection?


Teaching Evolution: Richard C. Lewontin: The genetic basis of evolutionary change

May 10, 2018 • 11:00 am

by Greg Mayer

Our seventh installment of Teaching Evolution is an extract from The Genetic Basis of Evolutionary Change by Richard C. Lewontin. As regular WEIT readers will know, Dick was Jerry’s Ph.D. dissertation advisor (and mine too in the de jure sense, since my de facto advisor, Ernest E. Williams was retired). In this book, Dick summarized and critiqued the initial results of the “find ’em and grind ’em” school of population genetics, which studied electrophoretically detectable allelic variation in soluble proteins. In the extract chosen, he lays out the basic questions of population genetics, and how, historically, they have been addressed. It turns out that protein electrophoretic data were inadequate to our needs, leading to a further “struggle to measure variation”, leading eventually to nucleotide sequencing.  The last of Dick’s books mentioned below is a collection of reviews from the New York Review of Books; it contains “Sex, Lies, and Social Science” (and the subsequent exchange), which along with Peter Medawar’s takedown of Teilhard de Chardin, and E.E. Williams’ takedown of Soren Lovtrup, is among the best book reviews ever.

Richard C. Lewontin (b. 1929) is Alexander Agassiz Professor of Zoology Emeritus in the Museum of Comparative Zoology at Harvard University. One of the most influential population geneticists of the 20th century, he studied under Th. Dobzhansky at Columbia. His work has centered around what he has called “the struggle to measure variation”, and the interpretation of that variation in terms of the evolutionary forces acting on populations. In 1966, he and Jack Hubby at the University of Chicago, and, independently Harry Harris in England, introduced the technique of protein gel electrophoresis to the study of genetic variation in natural populations and showed that there is abundant variation in nature. His student Marty Kreitman was the first to use DNA sequencing to study variation, which, like electrophoresis before it, has revolutionized empirical population genetics. Lewontin’s books include The Genetic Basis of Evolutionary Change (1974), Human Diversity (1982), The Triple Helix (2000), and It Ain’t Necessarily So: the Dream of the Human Genome and Other Illusions (2000).

Lewontin, R. C. 1974. The Genetic Basis of Evolutionary Change. Columbia University Press, New York. Extracts from Chap. 1, “The Structure of Evolutionary Genetics” (pp. 3-6), and Chap. 2, “The Struggle to Measure Variation” (pp. 19-38 and pp. 86-94). (access to entire book)

Study Questions:
1. What does Lewontin see as the most essential part of Darwin’s contribution? Why does this contribution make the study of genetic variation crucial for the study of evolution?

2. What are the “classical” and “balance” schools of population genetics? What are the views of these schools on the nature and amount of variation in natural populations, the modes of natural selection acting in natural populations, and the genetics of speciation?

3. What degree of variability in populations is inferred from the study of visible mutations, and from the study of the results of artificial selection? How do these estimates compare to one another?

4. How would DNA sequences, as opposed to mere identification of protein alleles (as is done in electrophoresis), provide richer information for addressing the questions posed by Lewontin? In particular, how would they provide better data on the nature of selection? (The answer to this is not in the reading.)

Teaching Evolution: Alfred Russel Wallace: Geographical distribution

May 2, 2018 • 12:30 pm

by Greg Mayer

Our sixth installment is a paper by Alfred Russel Wallace. Written while he was still collecting in the Malay Archipelago, it is a foundational work in zoogeography, in which Wallace invokes a long history of evolutionary changes of organisms, and geographical changes of the land and water, to account for organisms’ current distributions and affinities. Readers may recall that 2013 was the centenary of Wallace’s death, and that we posted a series of commemorative posts on Wallace here at WEIT to celebrate his accomplishments during that year.  (Follow this link for many WEIT postings on Wallace.)

Alfred Russel Wallace (1823-1913) was co-discoverer, with Charles Darwin, of natural selection. A gentleman but from a family of lesser means than Darwin, he was largely self-taught. He first made a name for himself by conducting an expedition to the Amazon (1848-1852) with Henry Bates; unfortunately, most of his specimens were lost when his ship sank on the return to England. Setting out again on a natural history collecting expedition, he traveled in the Malay Archipelago from 1854-1862. It was at Ternate in 1858, that, during a bout of malaria, the concept of natural selection came to him. Wallace is widely acknowledged as the greatest figure in the history of zoogeography. A lifelong friend of Darwin, in later life he became a staunch public advocate of socialism and, much to the chagrin of his scientific colleagues, spiritualism. His books include The Malay Archipelago (1869), Contributions to the Theory of Natural Selection (1870, a collection of his papers, including the important ‘Sarawak’ and ‘Ternate’ papers), his monumental The Geographical Distribution of Animals (1876), Island Life (1880), and Darwinism (1889). Andrew Berry has edited a wide ranging anthology of Wallace’s writings, Infinite Tropics (2002).  All of Wallace’s published works are available at John van Wyhe’s superb Wallace Online.  A modern, scientific biography is Peter Raby’s Alfred Russel Wallace: A Life (2002).

Wallace, A.R. 1860. On the zoological geography of the Malay Archipelago. Journal of the Proceedings of the Linnean Society, Zoology 4:172-184.

Study Questions:
1. The comparison of which particular islands’ faunas helped Wallace epitomize the nature of the boundary between the Indian (= Oriental) and Australian regions? What are the geographic, climatic, and geological circumstances of these islands? What are their faunal differences and similarities?

2. What importance does Wallace place on the depth of the sea? Show how he uses it in accounting for the geographical distribution of animals.

3. What explanatory principles does Wallace invoke to explain the phenomena he discusses? What do these principles reveal about Wallace’s thinking at the time he wrote this paper?


Teaching Evolution: Alfred Sherwood Romer: Life’s story

April 25, 2018 • 11:30 am

by Greg Mayer

Our fifth installment of Teaching Evolution is a paper by A.S. Romer describing a new species of mammal-like reptile that has a dual jaw joint– the old reptilian one, plus a nascent mammalian one. (In reptiles, the jaw joint is between the quadrate bone of the skull and the articular bone of the lower jaw; in mammals it’s the squamosal and dentary, respectively. We’ve discussed this previously at WEIT.) The transition from reptiles to mammals is one of the most completely exemplified major evolutionary changes in the fossil record. That the ancestors of mammals were to be sought among a particular group of fossil reptiles (synapsids) has been known since the late 19th century, from the work of British anatomist Richard Owen and American paleontologist Edward Drinker Cope. Since then, the story of how this transition occurred, with the bones of the reptilian jaw joint   becoming ear ossicles in mammals, while a new jaw joint evolved, has been worked out in exquisite detail. This paper by Fuzz Crompton and Farish Jenkins gives an overview of the story, and this paper by Luo Zhe Xi has the latest developments.

In the readings I give to the students in my evolution class, I like to include some papers reporting particular findings (such as this one), as well as review papers or book extracts (such as the earlier installments). Most of the scientific literature is, of course, reports of particular findings.

Alfred Sherwood Romer (1894–1973) was for many years the dean of American vertebrate paleontology. A student of William King Gregory at Columbia University, he spent much of his early career at the University of Chicago, before moving to Harvard’s Museum of Comparative Zoology. At the MCZ, he eventually became director, in which position he recruited to the Museum such luminaries as G. G. Simpson and Ernst Mayr. Unlike these colleagues, however, Romer devoted most of his work to the study of evolutionary history, rather than evolutionary mechanisms, publishing on vertebrates of all kinds and times, but specializing on amphibians and reptiles of the Paleozoic and Triassic. He wrote several highly influential textbooks and monographs, including Man and the Vertebrates (1st ed., 1933), Vertebrate Paleontology (1st ed., 1933), The Vertebrate Body (1st ed., 1949), and Osteology of the Reptiles (1956). Edwin Colbert (1982) gives a brief summary of his life and work.

Romer, A.S. 1969. Cynodont reptile with incipient mammalian jaw articulation. Science 166:881-882. (This will get you the paper only if you or an institution you are affiliated with has a subscription; if not, judicious inquiry might yield you a copy.)

Study Questions:
1. Why is Diarthrognathus, despite its possession of a double jaw joint, not considered an evolutionary reptile-mammal transition form? What, according to Romer, is the phylogenetic position of Probainognathus, and why does he think so?

2. Given what you know about paleogeography, what do you think about the fact that cynodonts (advanced mammal-like reptiles) of the early Triassic are found in South Africa, while the even more advanced cynodonts described from the Middle Triassic by Romer are from South America?

3. What skeletal feature has reached an essentially mammalian stage in Probainognathus and its relatives (the chiniquodonts)?
[The other installments of Teaching Evolution can be found by clicking ‘MOOC’, under “filed under” or “tags”, just below.]

Teaching Evolution: Charles Lyell: The principles of geology

April 19, 2018 • 10:45 am

by Greg Mayer

Our fourth installment of Teaching Evolution is an extract from Principles of Geology, by Charles Lyell. Lyell was an enormously influential scientist, and a leading figure in scientific circles in 19th century Britain. His influence on Darwin was profound: in Janet Browne’s authoritative biography of Darwin, the entry for Lyell in the index of volume one goes on for 28 lines, and for 27 lines in the second volume!

In the first half of the 19th century, the links between biology and geology were much closer that they are now. Both were branches of natural history, and Darwin first made his name as a geologist, before his more biological contributions came to dominate his reputation. Lyell’s Principles were required reading for anyone involved in discussions of organic evolution. The current divorce between the academic disciplines is regrettable.

When I was helping plan a major in ecology, evolution, and conservation a few years ago, a survey of a broad range of the best undergraduate majors across the United States showed that none required any geology (though many required years of chemistry and/or physics). A notable innovation of our new major was that it required foundational work in geology for students in the biological sciences. (The major, unfortunately, was nixed by our dean before it got implemented.)

Charles Lyell (1797-1875) is perhaps the greatest geologist of all time. As the American paleontologist David Raup once remarked, “Lyell is to geology what Darwin is to biology.” Lyell’s signal achievement was to turn geologists to the study of observable physical, chemical, and biological processes, and to make these processes the first choice when seeking explanations for the events of Earth history. His method may be epitomized by the phrase “the present is the key to the past”. Born in Scotland and trained as a lawyer, for most of his life he supported himself and his family by the sales of his books. A close friend of Darwin’s, he helped arrange the first publication of Darwin’s views on natural selection, alongside Wallace’s independent discovery of the same principle. Despite this, Lyell did not accept evolution until several years after the publication of the Origin. Lyell’s masterwork, Principles of Geology (1st ed. 1830-1833), which went through 11 editions in his lifetime, was informed by his wide field experience in Europe and North America. He is buried, like Darwin, in Westminster Abbey.

Lyell, C. 1830-1833. Principles of Geology, Being an Attempt to Explain the Former Changes of the Earth’s Surface, by Reference to Causes Now in Operation. Three volumes. John Murray, London. Vol. 3, Chaps. I, IV.

Study Questions:
1. What does Lyell identify as the chief impediment to the first geologists achieving a sound theory of the Earth’s history?

2. What types of studies have led to progress in geology?

3. How may the relative ages of rocks be determined? What sort of evidence does Lyell consider the most useful in this regard?

4. What does Lyell mean by a “zoological province”? How does he use this concept to help establish chronology?

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

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

April 12, 2018 • 10:30 am

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.]

Teaching Evolution: A.W.F. Edwards: The coral of life

April 3, 2018 • 1:45 pm

by Greg Mayer

Our second installment of Teaching Evolution is a paper by A.W.F. Edwards on the history and logical justification of methods of phylogenetic inference. In teaching evolution, the idea of the history of life is very important. Most students intuitively see the closer genealogical relationship between, say, a man and an ape than a dog, or among any of those as compared to a salmon. But the precise logic of doing so, especially when the degree of genealogical propinquity is less evident, is not easy to convey. I now teach this subject using a likelihood-based logic of justification, and Edwards was a pioneer in this area. Although we are accustomed now to think and speak of the phylogenetic tree as a “tree of life”, Darwin at first referred to it in his notebook as “the coral of life”, which is a more apt analogy, in that only the tips are alive, while the bases of the branches are dead.

For the first installment of what Jerry has called our “mini-MOOC” on evolution– an extract from the Origin by Darwin– I left out the title I gave to that week’s topic in my course: “Unity of type and adaptation”. I’ve now revised the title of that installment to include this in its title. Unity of type and adaptation were the two great classes of organic phenomena that Darwin sought to explain with his theory of descent with modification; with the chief means of modification– natural selection— accounting for the fit of organic beings to their conditions of existence, i.e. their adaptations. Thus Darwin proposed to solve these two great unsolved problems of biology in the first half of the 19th century with a single, unified explanatory theory.

A.W.F. Edwards in Cambridge, by Joe Felsenstein, used with permission.

Anthony William Fairbank Edwards (b. 1935) is a British statistician, geneticist, and evolutionary biologist. He is a Life Fellow of Gonville and Caius College and Emeritus Professor of Biometry at the University of Cambridge. An undergraduate student of R. A. Fisher, he has written several books and numerous scientific papers. He is best known for his pioneering work, with L. L. Cavalli-Sforza, on quantitative methods of phylogenetic analysis, and for strongly advocating Fisher’s concept of likelihood as the proper basis for statistical and scientific inference. He has also written extensively on the history of genetics and statistics, including an analysis of whether Mendel’s results were “too good” (they were). His most influential book is Likelihood (expanded edition, 1992), in which he argues for the centrality and sufficiency of likelihood as an inferential principle, often using genetic examples to illustrate his argument.

Edwards, A. W. F. 1996. The origin and early development of the method of minimum evolution for the reconstruction of phylogenetic trees. Systematic Biology 45:79-91.

Study Questions:
1. What was Edwards’ purpose in writing this paper?

2. What is Ockham’s razor? What is the “Darwin principle”? What is the relationship between them?

3. What are some of the various ways in which a method of minimum evolution may be used to estimate phylogeny? What, according to Edwards, is the justification for any of these methods?

[For further discussion of the history of phylogenetic methods, see chapter 10, “A digression on history and philosophy”, in Joe Felsenstein‘s Inferring Phylogenies (Sinauer, 2004).]

Teaching Evolution: Darwin: Unity of type and adaptation

March 31, 2018 • 10:30 am

Note from Jerry: Greg plans to run a mini-MOOC here, so if you want some education in evolution, do the readings and answer the questions (to yourself). This is the first installment.

by Greg Mayer

This semester I’m teaching BIOS 314 Evolutionary Biology, an upper level undergraduate course. The students are all or mostly biological sciences majors, and general genetics and biostatistics are prerequisites for taking the course. As a textbook, I use Evolution, by Doug Futuyma and Mark Kirkpatrick, published by Sinauer Associates of Sunderland, Mass., which last year became an imprint of Oxford University Press. This is the 4th edition of the current iteration of this text, which also had 3 editions under an earlier iteration with the title Evolutionary Biology. Doug was my undergraduate evolution teacher, and I took the class with him while he was writing the first edition of Evolutionary Biology.

I hope to say more about the textbook later, but I also have the students read a series of what I regard to be classic papers or extracts– one each week–and these are what I want to share with WEIT readers. Each reading is accompanied by a brief biography and illustration of the author, and a small number of study questions, designed to guide the student in understanding the reading. I sometimes assign these questions as homework essays, or include them on exams. The first week’s reading each time I’ve taught the course this way has been an extract from the Origin. I will, when possible, provide links to the readings. For this Darwin reading, you can use John van Wyhe‘s superb Darwin Online. I’ll be posting a reading every few days. If you want to read along, it will be like taking a guided readings course in evolutionary biology.

Charles Darwin (1809-1882), after studying briefly at Edinburgh to be a physician, went to Cambridge to prepare for the Anglican priesthood. While there, his interest in natural history attracted the attention of his professors, which led to him being invited aboard H.M.S. Beagle as a supernumerary naturalist for that survey vessel’s global circumnavigation (1831-1836). By the time he returned he was already a recognized geologist, and, leaving the ministry behind, he soon established himself as a rising star in all departments of natural history. After study of his Beagle collections convinced him that species were not immutable, he discovered natural selection as a means of modification. Spurred by the later but independent discovery of natural selection by A. R. Wallace, he published his views and evidence in On the Origin of Species in 1859. Within a few years, the whole of the scientific community accepted descent with modification as the key process underlying the phenomena of the organic world, though natural selection as the chief means of modification was not accepted during Darwin’s lifetime. Among his many other works are Zoology of the Beagle (1838-1843, edited by Darwin), Voyage of the Beagle (2nd ed., 1845), Variation Under Domestication (1868) and The Descent of Man (1871). All of Darwin’s published works are available at John van Wyhe’s Darwin Online, http://darwin-online.org.uk/. He is buried in Westminster Abbey, not far from Sir Isaac Newton. The best biography is Janet Browne’s Charles Darwin (vol. 1, 1995; vol. 2, 2002).


Darwin, Charles. 1859. On the Origin of Species. 1st ed. John Murray, London. Extract from Chap. 13, pp. 434-450, “Morphology” and “Embryology”.


Study Questions:

1. Why is the concept of homology crucial for even being able to talk about organic structure? How are homologous organs recognized? What is Darwin’s explanation for homology?

2. How does Darwin’s account of serial homology (the resemblance of parts within an organism, for example, the forelimbs to the hindlimbs, or of a cervical vertebra to a thoracic vertebra) depend on the repetition of parts or segmentation?

3. What is the “law of embryonic resemblance”? How do these resemblance relate to the organisms’ conditions of existence? How does this relation depend on whether the embryo is active and provides for itself?

4. When during development does Darwin suppose most species differentiating characters to become evident? How does this relate to when he supposes the characters to affect the survival and reproduction of their bearers?