A perversion or prevention of true inheritance is also seen in the action of alcohol, or excessive overwork, or any other cause which by originating morbid conditions in individuals may also injure the reproductive elements.
These forms of quasi-inheritance are, of course, highly important so far as the improvement of the race is concerned. So, too, is the fact that improved or deteriorated habits and thoughts are transmitted by personal teaching and influence and are cumulative in their effect. But all this must not be confounded with the inheritance of acquired characters. Cases of quasi-inheritance may perhaps be most readily distinguished from cases of true inheritance by the time test. When a modification acquired in adult life is promptly communicated to the child in early life or from birth, it may rightly be suspected that the inheritance, like that of money or title, is not truly congenital, but is extraneous or even anti-congenital in its nature. Judged by such a standard, the inherited injuries in Brown-Séquard's guinea-pigs are only exceptional cases of quasi-inheritance, and are not necessarily indicative of any general rule affecting true inheritance.
FOOTNOTES:
[54] A very able anatomist of my acquaintance denies the inheritance of mutilations and injuries, although he strongly believes in the inheritance of the effects of use and disuse.
[55] Variation of Animals and Plants under Domestication, i. 467-469. Lost toes were only seen by Dr. Dupuy in three young out of two hundred. Obersteiner found that most of the offspring of his epileptic guinea-pigs were injuriously affected, being weakly, small, paralysed in one or more limbs, and so forth. Only two were epileptic, and both were weakly and died early (Weismann's Essays, p. 311). A morbid condition of the spinal cord might affect the hind limbs especially (as in paraplegia) and might occasionally cause loss of toes in the embryo by preventing development or by ulceration. Brown-Séquard does not say that the defective feet were on the same side as in the parents (Lancet, Jan., 1875, pp. 7, 8).
[56] Variation of Animals and Plants under Domestication, ii. 57.
[57] Ibid., ii. 392. Perhaps it might be better to suppose that the best gemmules were sacrificed in repairing the injured nerve, and hence only inferior substitutes were left to take their place, and could only imperfectly reproduce the injured part of the nervous system in offspring.
[58] Hence perhaps Mr. Spencer's error in representing the epileptic liability as permanent and as coming on after healing (Factors of Organic Evolution, p. 27).
[59] It is not claimed that the imperfect foot was on the same side of the body as in the parent, and where parents had lost all the toes of a foot, or the whole foot, the few offspring affected usually had lost only two toes out of the three, or only a part of one or two or three toes. Sometimes the offspring had toes missing on both hind feet, although the parent was only affected in one. One diseased ear and eye in the parent was "generally" or "always" succeeded by two equally affected ears and eyes in the offspring (cf. Pop. Science Monthly, New York, xi. 334). The important law of inheritance at corresponding periods was also set aside. Gangrene or inflammation commenced in both ears and both eyes soon after birth (pointing possibly to infection of some kind); the epileptic period commenced "perhaps two months or more after birth," while the loss of toes had occurred before birth. In no case, as Weismann points out, is the original mutilation of the nervous system ever transmitted. Even where an extirpated ganglion was never regenerated in the parent, the offspring always regained the part in an apparently perfect condition. On the whole the conflicting results ought to be as puzzling to those who may attribute them to a universal tendency to inherit the exact condition of parents as they are to those who, like myself, are sceptical as to the existence of such a law or tendency.
[60] The various results need to be fully and impartially recorded, and they should also be well tested and confirmed in proportion as they appear improbable and contrary to general experience. Professor Romanes has been carrying out the necessary experiments for some time past.