Darwin's On the Origin of Species. Daniel Duzdevich
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some very distinct variety for breeding, then it would be too obvious to even discuss. But its importance lies in the dramatic effect of unidirectionally accumulating minute differences imperceptible to the untrained eye – mine included – over many generations. Very few men are discerning enough and in possession of the proper judgment to become eminent breeders. Even with these gifts, he will only make improvements by studying his subject for years and devoting a lifetime to his task with indomitable perseverance. Few would believe the talent and practice necessary to become even a skillful pigeon breeder.
These concepts also apply to horticulture, although the variations tend to be more abrupt. No one supposes that the choicest productions arose by a single variation in an original stock. This can be proven in some cases, for records have been kept; the steadily increasing size of the gooseberry is one example. The astonishing improvements in florists’ flowers are apparent when present-day varieties are compared with drawings made only twenty or thirty years ago. Seed raisers do not need to pick out the best specimens from a well-established plant variety, but simply pull up the “rogues,” as they call plants that deviate from the defined standard. This kind of selection is also followed with animals, because no one is careless enough to let the worst animals breed.
Another way to observe the accumulated effects of selection is by comparing the diversity of flowers of different varieties of one flower-garden species; the diversity of leaves, pods, tubers, or other valued parts of kitchen-garden species; or the diversity of fruits of a species in the orchard relative to other parts of the same variety. Notice how different the leaves of a cabbage are but how alike the flowers; how different the flowers of a heartsease are but how alike the leaves; how much the gooseberry fruit differs in size, color, shape, and fuzziness but how similar the flowers are. It’s not that varieties differing drastically in one way don’t differ in others. In fact, this is rarely the case. Correlated growth, which should never be underestimated, ensures some differences in other parts. However, as a general rule, selection for slight variations in a specific part will produce varieties differing mostly in that part.
Some may object that the principle of selection has been reduced to methodical practice for less than seventy-five years. It is true that it has been utilized frequently in recent years and accompanied by rapid and important results with many treatises published on the subject. All the same, it is not a modern discovery. I could give several references that acknowledge its importance in works of high antiquity. In rude and barbarous periods of English history, choice animals were often imported and laws were passed to prevent their exportation. The destruction of horses under a certain size was ordered, comparable to the “roguing” of plants mentioned earlier. I found that the principle of selection is clearly given in an ancient Chinese encyclopedia. Some of its explicit rules are written down by Roman classical writers. It is clear from passages in Genesis that the color of domestic animals was attended to at that early period. Indigenous groups sometimes cross their dogs with wild canines to improve the breed, both in the present day and – as attested by Pliny – in the past. The natives of South Africa mate their draft cattle by color, just as some of the Eskimo do for their dog teams. Livingstone reports that good domestic breeds are valued by inhabitants of Africa’s interior who have not associated with Europeans. Some of these examples do not demonstrate actual selection, but they show that breeding of domestic animals was done in ancient times and is now done by indigenous peoples. It would be strange if attention had not been paid to breeding, the inheritance of good and bad qualities being so obvious.
Today, breeders try to make a superior and novel strain or sub-breed by methodical selection with a preconceived object in view, but for this discussion a type of selection I call “unconscious” is more important; it results from everyone trying to possess and breed from the best individual animals. For example, a man who keeps pointers will obviously try to obtain the best dogs he can and then breed from the best of his own. He has no intention or expectation of permanently altering the breed, but this process, extended over centuries, will modify any breed. Using this same process, only more methodically, Bakewell, Collins, and others greatly modified, even during their own lifetimes, the forms and qualities of their cattle. These kinds of gradual and unobservable changes could never be recognized in the absence of measurements or careful drawings made long ago for comparison. In some cases, unchanged or slightly changed individuals of a known breed can be found in less civilized regions where the breed has been less improved. The King Charles spaniel may have been extensively modified unconsciously since the time of its namesake. Some authorities assert that the setter is directly derived from the spaniel, and the English pointer is known to have been greatly changed over the last century, probably by crosses with the foxhound. Importantly, change has been effected unconsciously and gradually but so effectively that although the old Spanish pointer came from Spain, there is no native dog in Spain like the English pointer.6
Through a similar process of selection, coupled with careful training, English racehorses have come to surpass their parent Arab stock in speed and size so that by the regulations of the Goodwood Races, they are favored in the weights they carry. Lord Spencer and others have shown that English cattle have increased in weight and early maturity compared to the stock once kept in this country. The stages through which carrier and tumbler pigeons have passed, and how they have come to differ so greatly from the rock pigeon, can be traced by comparing accounts given in old treatises with modern British, Indian, and Persian breeds.
Youatt gives an excellent example of unconscious selection in which the breeders in question could never have expected or even wanted to produce two distinct strains. He remarks that the two flocks of Leicester sheep kept by Mr. Buckley and Mr. Burgess “have been purely bred from the original stock of Mr. Bakewell for upward of fifty years. There is not a suspicion existing in the mind of any one at all acquainted with the subject that the owner of either of them has deviated in any one instance from the pure blood of Mr. Bakewell’s flock, and yet the difference between the sheep possessed by these two gentlemen is so great that they have the appearance of being quite different varieties.”
There may be peoples so barbarous that they never consider the inherited characteristics of their domestic animals, but if an animal is particularly useful to them for some special reason, it will be preserved during famines and other accidents and consequently leave more offspring than its inferior brethren; this is a kind of unconscious selection. The value of animals is demonstrated even among the barbarians of Tierra del Fuego who kill and devour their old women during times of dearth, as of less value than their dogs.
In plants the same gradual process of improvement through occasional preservation of the best individuals can be recognized in the larger size and more intense beauty of modern heartsease, rose, geranium, dahlia, and other varieties when compared to older varieties or parent stocks. (This applies whether or not the individuals can be classified as belonging to a distinct variety on first appearance, and whether or not species or varieties had been blended by crossing.) No one would expect to get a first-rate heartsease, dahlia, or melting pear from the seed of a wild plant. Although the pear was cultivated in classical times, Pliny’s descriptions suggest it was a fruit of very inferior quality. Horticultural essays convey surprise about the gardener’s wonderful skill in generating splendid products from such poor materials, but the art has been simple: the final result proceeds from an almost unconscious process. It has always involved cultivating the best-known variety, sowing its seeds, and selecting slightly better varieties when they happen to appear. The gardeners of classical times cultivated the best pear they could procure with no intention of providing us with such sweet fruit, and yet in part we owe to them our pear, because they naturally chose and preserved the best varieties they found.
The large amount of change that has been slowly accumulated unconsciously in cultivated plants explains why we cannot recognize the parent stocks of many established kitchen- and flower-garden varieties. If it took centuries or millennia of improvement to create useful plants, we can understand why Australia, the Cape of Good Hope, and other regions inhabited by uncivilized peoples have not afforded us a single plant worth culture. It is not that these species-rich countries lack original stocks of useful plants, but that these native plants have not been improved to a standard of perfection by continuous selection as in anciently civilized regions.
Domestic animals kept by