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?

30 thoughts on “Teaching Evolution: Darwin: Unity of type and adaptation

  1. I’ll give it a shot.

    How are homologous organs recognized? What is Darwin’s explanation for homology?

    Homology is the “dead hand of history” that limits evolution and its possibilities. A bird still grows a hand that reveals the bones that used to become articulated in non-avian dinosaurs, only now they fuse together to make a rigid section of one of its wings.

    It’s an absurd way to design anything, while evolution has no choice but to use what heredity has bequeathed to it.

    Glen Davidson

  2. What a pleasure it must be to teach an evolution course that has genetics for a prerequisite. Before I retired, I labored to teach a modern evolutionary biology course that lacked one (so forget Futuyma as a text). I look forward to these postings, and I hope lots of WEIT readers do the reading and think about the questions.

      1. pdf’s of the 1859 first edition of the Origin can also be downloaded (free, of course) from archive-org.

  3. Of Darwin’s books (apart from ‘The Voyage…’ which is basically a travel book) “The Expression of the Emotions in Man and Animals” is the one I like best, for one reason or other.

  4. Thank you so much for this. I don’t know if these are right but this is what I got from reading those pages.

    1. It’s crucial because the similarities are too obvious to ignore. Homologous organs are recognized by their similarities among one another. For example, as Darwin pointed out, the hand, the paddle, and the wing, are homologous. Darwin’s explanation for homology is either – I’m not sure – is something along the lines of a common ancestor but I don’t believe he uses those words, or the similarity in the embryos going further back.

    2. I don’t know. In looking at this question, I understand that serial homology refers to the similarities between the spine and skull, for example, and the hand, paddle, wing homology is called something different.

    3. I believe it’s that most embryos resemble one another within and among groups at first and then change. The resemblance relates to the condition of existence because as there is pressure to survive, the embryo changes. The resemblance depends on whether or not the embryo has pressure to provide for itself.

    4. I believe this is when there is pressure on the embryo to be active and survive. It could be during metamorphosis or in early or late maturity of the organism. I’m not sure I understand the second part to this question.

    This was really, really interesting.

  5. I am also teaching upper biology majors evolution class with statistics and genetics as pre-requisites. I am interested to follow along!

  6. I love that stats is a requirement. My course requires genetics as a prerequisite. While it is obviously very helpful, I find myself struggling when the students don’t understand some of the simplest math (not even stats) involved. I, too, am using this text both fall and spring this year. I’ve found the exercises to be most helpful in demonstrating many concepts, especially the simulations. I look forward to following along. Good luck!

  7. I had forgotten how much Darwin relied on “terminal addition” to explain the conserved parallelism in ontogeny of related species. Ernst Haeckel pretty much followed Darwin on this point and was probably no more a Lamarckist, despite S.J. Gould’s smears, than was Darwin himself. Where Darwin writes on p. 449 “. . . community in embryonic structure reveals community of descent,” he could equally well have written “ontogeny recapitulates phylogeny”.

    1. No, I think that’s not right. Darwin is very von Baerian, rather than Haeckelian, in his approach to embryology. His remarks on Agassiz, not being able to tell early embryos apart because he neglected to label them, shows this clearly. Darwin’s law of embryonic resemblance is not “ontogeny recapitulates phylogeny”. Rather, embryos of the same group resemble other embryos in that group (e.g., Agassiz’s mammal and reptile); it is not adults that resemble embryos, as they would if ontogeny recapitulated phylogeny. Later development is not addition– it is divergence. Embryology is thus a striking representation of the unity of type.

      Darwin also proposes that natural selection may alter an embryo at any stage of development, if the embryo is called upon to be “active, and has to provide for itself.”


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