Acquired Qualities
When an organism has been subjected to abnormal conditions in life it can transmit any peculiarity it may have acquired. This is, however, not always possible, otherwise descendants of men who have lost their arm or leg would be born without the corresponding arm or leg—this shows that some acquired qualities are more easily transmitted than others—although there are cases, as, for instance, a race of dogs without tails has been produced by cutting off the tails of both sexes of the dog, during several generations. “A few years ago,” says Haeckel, “a case occurred on an estate near Jena in which, by the careless slamming of a stable-door, the tail of a bull was wrenched off, and the calves begotten by this bull were all born without a tail. This is certainly an exception; but it is very important to note the fact that under certain unknown conditions such violent changes are transmitted in the same manner as many diseases.” The transmission of diseases such as consumption, madness, and albinism form examples. Albinoes are those individuals who are distinguished by the absence of coloring matter from their skins; they are of frequent occurrence among men, animals and plants. Among many animals, such as rabbits and mice, albinoes with white fur and red eyes are so much liked that they are propagated. This would be impossible were it not for the law of the transmission of adaptations. Hornless cattle have descended from a single bull born in 1770 of horned parents, but whose absence of horns was the result of some unknown cause.
The law of interrupted or latent transmission, as illustrated in grandchildren who are like the grandparents, but quite unlike the parents. Animals often resume a form which have not existed for many generations. One of the most remarkable instances of this kind of reversion, or “atavism,” is the fact that in some horses there sometimes appear singular dark stripes similar to those of the zebra, quagga, and other wild species of African horse.
Nutrition directly modifies adaptation, as is well illustrated by animals which have been bred for domestic or other purposes. If a farmer is breeding for fine wool he gives much different food to the sheep than he would if he wished to obtain flesh or an abundance of fat. Even the bodily form of man is quite different according to its nutrition. Food containing much nitrogen produces little fat, that containing little nitrogen produces a great deal of fat. People who by means of Banting’s system, at present so popular, wish to become thin, eat only meat and eggs—no bread, no potatoes.
Man can breed for milk in cattle, for feathers in pigeons, for colored flowers in plants, and, in fact, for almost any desirable quality.