This is from my forthcoming book with Malte Ebach.
Floyer’s monster pigs and his use of homologies to eliminate the interspecies breeding claim
In 1699, John Floyer reported upon a claim of interspecies breeding: human–pig. He had shown to him by a breeder in Staffordshire a new-born pig with what appeared to be a human face:
Contrary to the claim made by some that this was due to interbreeding between humans and pigs, a view quite common in the literature on natural history from the Greeks through to the modern era, Floyer observes that the teeth, pelt, nose, and bones are generally those of a pig, and that the similarity to human faces is due to distortion “whilst the Bones were Cartilaginous” in utero. He thinks it is due to mechanical distortion, but whatever we might now think of fetal deviation in development after such things as the thalidomide scandal, Floyer is using homology to overcome a mistake in classification made on the basis of analogy. He wrote:
I was further convinced in Opinion that there was really no mixture of the two Species in this Monster, by the Woman’s account who saw the Sow take the Bore[sic], and after the sixteen Weeks, on the beginning of the seventeenth, which is the usual time, the Sow pigged [bore] eight Pigs, the first five were perfect Pigs, the sixth was the Monster, and after that two more perfect Pigs, all which I saw sucking the Sow, and as well shaped, and as large as possible…
Floyer is appealing not only to the species homologies of anatomy, but also to the species homology of development. He makes this explicit, when thinking of the Mule:
… the Female contains in her Eggs the first Rudiments of the Animal of her Species, and … the impregnation only changes some of the extremities into resemblance of the Male.
This is a view widely held at the time: the male changes but does not cause the inheritance of the species-typical traits. He goes on to argue that this is a general law of biological inheritance. Assigning a monster to a single species is a remarkably modern thing to do for the late 17th century. Most monsters were thought to be hybrids from Aristotle’s writing onwards. That he uses observation rather than theoretical presumptions is telling also, but clearly what is observed are traits that are held to be somehow informative as to the taxonomic relations between pigs and humans.
Floyer, John, and Edward Tyson. 1699. A Relation of Two Monstrous Pigs, with the Resemblance of Humane Faces, and Two Young Turkeys Joined by the Breast. Philosophical Transactions of the Royal Society of London 21:431-435.