August Weismann is one of the great figures in the history of heredity; I can't remember exactly where I first really heard about him, but I suppose I'd been reading Francois Jacob and Jacques Roger and had mentally earmarked Weismann's 1889 Essays on Heredity and Kindred Biological Problems as a most-coveted book that I couldn't wait to lay my hands on.
So there I was at the British Library (I see from my notes that it was December 2003, I had a ridiculously long and varied list of desiderata!) just drooling for the large quantities of good stuff that awaited me, but of course sometimes the things you've most been looking forward to in advance turn out to be greatly disappointing, dry or irrelevant or whatever. So it was incredibly exciting that Weismann (his contemporary translators did right by him, I think) had one of those electrifying voices that speaks to you across the intervening hundred and twenty years as if they were nothing.
Here's a bit of what I have to say in the book:
In an essay titled “On the Supposed Botanical Proofs of the Transmission of Acquired Characters” (1888), Weismann provides a remarkably elegant refutation of the argument that acquired characters are passed on to offspring. His discussion makes it very clear both that the revival of Lamarckism (supported by Darwin’s development of the theory of pangenesis) was a dominant feature of the current scientific landscape and that this theory was very closely linked to the continuing belief in the power of the maternal imagination.
Weismann proposes a series of systematic experiments in mice as the initial step necessary for disproving the hypothesis, but he also observes with regard to humans that “the mutilations of certain parts of the human body, as practised by different nations from times immemorial, have, in not a single instance, led to the malformation or reduction of the parts in question. Such hereditary effects have been produced neither by circumcision, nor the removal of the front teeth, nor the boring of holes in the lips or nose, nor the extraordinary artificial crushing and crippling of the feet of Chinese women.”
“Not every post hoc is also a propter hoc,” he argues: “Nothing illustrates this better than a comparison between the ‘proofs’ which are even now brought forward in favour of the transmission of mutilations and the ‘proofs’ which supported the belief in the efficacy of so-called ‘maternal impressions’ during pregnancy, a belief which was universally maintained up to the middle of the present century.”
He notes that only one year earlier, a respectable scientific journal had reprinted an 1864 story about a pregnant merino sheep who broke her right fore-leg and gave birth four months later to a lamb that “possessed a ring of black wool from two to three inches in breadth round the place at which the mother’s leg had been broken, and upon the same leg”:Now if we even admitted that a ring of black wool could be looked upon as a character which corresponds to the fracture of the mother’s leg, the case could not possibly be interpreted as the transmission of a mutilation, but as an instance of the efficacy of maternal impressions; for the ewe was already pregnant when she fractured her leg. The present state of biological science teaches us that, with the fusion of egg and sperm-cell, potential heredity is determined. . . . Such tales, when quoted as ‘remarkable facts which prove the transmission of mutilations,’ thoroughly deserve the contempt with which they have been received by Kant and His. When the above-mentioned instance was told me, I replied, “It is a pity that the black wool was not arranged in the form of the inscription ‘To the memory of the fractured leg of my dear mother.’”
No theory could survive such an assault. And yet Weismann’s radical skepticism is matched by a wry awareness of how attractive such explanations can be: “The readiness with which we may be deceived is shown by the fact that I myself nearly became a victim during the past year (1888),” he confesses, telling the story of a friend whose ear is marked by a scar from a duelling sword and whose daughter has a very similar mark on her ear (442). Only when Weismann looks at the friend’s other ear and notices it has the same ridge does he recognize the mark as a hereditary rather than an acquired character.