Thanks viator, that's really interesting. Your post also jogged my memory that I was going to post interesting response I got from HOPOS. Here's a collection of what I received:
Greg Radick wrote:
In haste, here's a few of things to consider and places to read about them:
(1) Darwin did have a theory of heredity, called pangenesis, which he published in 1868; and there's actually a line you can draw historically between that theory and Mendelian theory. For a decent popular tracing of that line, see the first third or so of James Schwartz's IN PURSUIT OF THE GENE: FROM DARWIN TO DNA (Harvard, 2008). Peter Bowler's THE MENDELIAN REVOLUTION (ca. 1990) is also still useful if dated in certain ways.
(2) However, Darwin conceived his studies of heredity as part of wider studies on "generation" -- an old category that linked heredity with reproduction, the healing of wounds, and other phenomena to do with the production of new living tissue. Hybridization studies took their place in a much more heterogeneous set of inquiries than one might expect. To get a feel for how different Darwin's conception was from what emerged 30 or so years later, check out Jim Endersby's summary in his chapter in THE CAMBRIDGE COMPANION TO DARWIN, eds. Hodge and Radick (2003, 2nd edition imminent) and, more extensively, Jon Hodge, "Darwin as a Lifelong Generation Theorist", in THE DARWINIAN HERITAGE, ed. Kohn (1985), and just reprinted in the second volume of Jon's collected papers, out with Ashgate Press.
(3) Not what your students are looking for, but they might also check out Desmond and Moore's new DARWIN'S SACRED CAUSE, which brilliantly shows how questions of hybridization, including what experimental hybridization reveals about pigeon ancestry, were all caught up with questions about human unity and American slavery when Darwin did his own pigeon breeding experiments.
Ian McKay wrote:
My guess would be that feather colour in pigeons, like hair colour and skin colour in many animals, is determined by multiple genes, not single genes. It would therefore be difficult to infer any simple mathematical rules of heredity from the results of Darwin's breeding experiments.
By contrast, the phenotypic traits that Mendel chose to study in pea plants were all examples of single-gene inheritance. Indeed, some authors think he must have selected these traits on that basis.
Jim Lennox wrote:
I want to strongly second Dr. McKay's note. You might have your students compare the material in ch. 1 on pigeon breeding with the later chapter on Hybridism, and especially the section entitled 'Hybrids and Mongrels Compared, independently of their Fertility' (272-6 in the Harvard facsimile). Darwin has studied the work of Kollreuter and Gartner very carefully (their work got Mendel excited about finding a law governing hybrid series), but because that work lacks the understanding of statistics and experimental controls that we see in Mendel's description of his methods, no consistent picture emerges.
Even more fun for your students, if they know a bit about Mendel's work, is to look at Darwin's discussion of Peas in The Variation of Animals and Plants Under Domestication, chapter 9, published in 1868, two years after Mendel's paper was published. Most of the characters that Mendel isolates for crossing are noted by Darwin, and he constantly notes that specialists talk about how the different varieties breed true for these characters, but it is apparently of little interest to Darwin what would happen if these true breeding varieties were crossed, other than whether the hybrid crosses are fertile or not. Darwin is very interested in the fact that while Pisum is treated by botanists as a genus with many species, and while there is a tendency for the varieties to breed true and not cross if left to themselves, they can easily be crossed and the resulting hybrids are fertile--one more example of the standard means of distinguishing species and variety breaking down. That seems to be the result he is most interested in.
