OTHER INHERITED INJURIES MENTIONED BY DARWIN.
Darwin quotes some cases from Dr. Prosper Lucas's "long" but weak and unsatisfactory "list of inherited injuries."[62] But Lucas was somewhat credulous. One of his cases is that many girls were born in London without mammæ through the injurious effect of certain corsets on the mothers. He also gives a long account of a Jew who could read through the thick covers of a book, and whose son inherited this "hyperæsthesia" of the sense of sight in a still more remarkable degree (i. 113-119). Evidently Lucas's cases cannot be accepted without some amount of reserve.
The cases of the three calves which inherited the one-horned condition of the cow, the two sons who inherited a father's crooked finger, and the two sons who were microphthalmic on the same side as their father had lost an eye, may be due to mere coincidence; or an inherited constitutional tendency or liability might lead to somewhat similar results in parent and offspring[63]—just as the tendency to certain fatal diseases or to suicide may produce similar results in father and son, although the artificially-produced hanging or apoplexy obviously cannot be directly transmitted. That more than one of the offspring was affected does not render the chances against coincidence "almost infinitely great," as Darwin mistakenly supposes. It "frequently occurs" that a man's sons or daughters may all exhibit either a latent or a newly-developed congenital peculiarity previously unknown;[64] and the coincidence may merely be that one of the parents accidentally suffered a similar kind of injury—a kind of coincidence which must of course occasionally occur, and which may have been partly caused by a latent tendency. The chances against coincidence are indeed great, but the cases appear to be correspondingly rare.
Darwin acknowledges that many supposed instances of inherited mutilation may be due to coincidence; and there is apparently no more reason for attributing inherited scars, &c., to any special form of heredity than to the effect of the mother's imagination on the unborn babe—a popular but fallacious belief in corroboration of which far more alleged instances could be collected than of the inheritance of injuries.
As an instance of the coincidences that occur, I may mention that a friend of mine has a daughter who was born with a small hole in one ear, just as if it were already pierced for the earring which she has since worn in it. I suppose, however, that no one will venture to claim this as an instance of the inheritance of a mutilation practised by female ancestors, especially as such holes are not altogether unknown or inexplicable, though very rarely occurring low down in the lobe of the ear.[65]
Many cases are known of the inheritance of mutilations or malformations arising congenitally from some abrupt variation in the reproductive elements. In such cases as the one-eared rabbits, the two-legged pigs, the three-legged dogs, the one-horned stags, hornless bulls, earless rabbits, lop-eared rabbits, tailless dogs, &c., if the father or the mother or the embryo had suffered from some accident or disease which might plausibly have been assigned as the cause of the original malformation, these transmitted defects would readily be cited as instances of the inheritance of an accidentally-produced modification.
The inheritance of exostoses on horses' legs may be the inheritance of a constitutional tendency rather than of the effect of the parents' hard travelling. Horses congenitally liable to such formations would transmit the liability,[66] and this might readily be mistaken for inheritance of the results of the liability. An apparent increase in this liability might arise from greater attention being now paid to it, or from increased use of harder roads; or a real increase might be due to panmixia and some obscure forms of correlation.
QUASI-INHERITANCE.
Of course artificially-caused ill-health or weakness in parents will tend in a general way to injure the offspring. But deterioration thus caused is only a form of quasi-inheritance, as I should prefer to call it. Semi-starvation in a new-born babe is not truly inherited from its half-starved mother, but is the direct result of insufficient nourishment. The general welfare of germs—as of parasites—is necessarily bound up with that of the organism which feeds and shelters them, but this is not heredity, and is quite irrelevant to the question whether particular modifications are transmitted or not.
Another form of quasi-inheritance is seen in the communication of certain infections to offspring. Not being transmitted by the action of the organism so much as in defiance of it, such diseases are not truly hereditary, though for convenience' sake they are usually so described.