The whole subject of inheritance is wonderful. When a new character arises, whatever its nature may be, it generally tends to be inherited, at least in a temporary and sometimes in a most persistent manner. What can be more wonderful than that some trifling peculiarity, not primordially attached to the species, should be transmitted through the male or female sexual cells, which are so minute as not to be visible to the naked eye, and afterwards through the incessant changes of a long course of development, undergone either in the womb or in the egg, and ultimately appear in the offspring when mature, or even when quite old, as in the case of certain diseases? Or again, what can be more wonderful than the well-ascertained fact that the minute ovule of a good milking cow will produce a male, from whom a cell, in union with an ovule, will produce a female, and she, when mature, will have large mammary glands, yielding an abundant supply of milk, and even milk of a particular quality?
Today is Charles Darwin’s birthday. I’m not such a serious Darwin reader, but it’s fun how it seems like you can open a Darwin book at almost any chapter and find something interesting or amusing. This is from The Variation of Animals And Plants Under Domestication, chapter twelve, ‘Inheritance’. Here we find Darwin overflowing with enthusiasm when trying to convince a sceptic about the importance of inheritance. In true Darwin style he launches into a long list of examples:
Some writers, who have not attended to natural history, have attempted to show that the force of inheritance has been much exaggerated. The breeders of animals would smile at such simplicity; and if they condescended to make any answer, might ask what would be the chance of winning a prize if two inferior animals were paired together? They might ask whether the half-wild Arabs were led by theoretical notions to keep pedigrees of their horses? Why have pedigrees been scrupulously kept and published of the Shorthorn cattle, and more recently of the Hereford breed? Is it an illusion that these recently improved animals safely transmit their excellent qualities even when crossed with other breeds? have the Shorthorns, without good reason, been purchased at immense prices and exported to almost every quarter of the globe, a thousand guineas having been given for a bull? With greyhounds pedigrees have likewise been kept, and the names of such dogs, as Snowball, Major, &c., are as well known to coursers as those of Eclipse and Herod on the turf. Even with the Gamecock, pedigrees of famous strains were formerly kept, and extended back for a century. With pigs, the Yorkshire and Cumberland breeders ”preserve and print pedigrees;” and to show how such highly-bred animals are valued, I may mention that Mr. Brown, who won all the first prizes for small breeds at Birmingham in 1850, sold a young sow and boar of his breed to Lord Ducie for 43 guineas; the sow alone was afterwards sold to the Rev. F. Thursby for 65 guineas; who writes, ”She paid me very well, having sold her produce for 300l., and having now four breeding sows from her.” Hard cash paid down, over and over again, is an excellent test of inherited superiority. In fact, the whole art of breeding, from which such great results have been attained during the present century, depends on the inheritance of each small detail of structure. But inheritance is not certain; for if it were, the breeder’s art would be reduced to a certainty, and there would be little scope left for that wonderful skill and perseverance shown by the men who have left an enduring monument of their success in the present state of our domesticated animals.
For the rest of the chapter, he will go on to talk about humans, again with long lists of examples, and then mixing in domestic animals and plants again. A lot of these examples of heredity surely hold up, and others seem like anecdotes. Here and even more in the following chapters–with subtitles including ‘reversion to atavism’, ‘prepotency’ and ‘on the good effects of crossing, and the evil effects of close interbreeding’–Darwin is trying hard to make sense of heredity. Why are certain features heritable? Why do they sometimes go away in the offspring but reappear in later generations? Why are offspring sometimes more like one parent than the other? In chapter 27, he will present his ‘provisional hypthesis of pangenesis’.
Darwin. 1875. The variation of animals and plants under domestication.