At the Naturalists' Congress in Wiesbaden in 1887, kittens with only stumps of tails were exhibited, and they were said to have inherited this peculiarity from their mother, whose tail, it was asserted, had been accidentally amputated. The newspapers reported that the case excited great interest, and biologists of the standing of Rudolf Virchow declared it to be noteworthy, and regarded it as a proof, if all the details of it were correct. From many sides similar cases were brought forward, intended to prove that the amputation of the tail in cats and dogs could give rise to hereditary degeneration of this part; even students' fencing-scars were said to have been occasionally transmitted to their sons (happily not to the daughters); a mutilated or torn ear-lobe in the mother was said to have given rise to deformity of the ear in a son; an injury to a father's eye was said to have caused complete degeneration of the eyes in his children; and deformity of a father's thumb, due to frostbite, was said to have produced misshapen thumbs in the children and grandchildren. A multitude of cases of this kind are to be found in the older textbooks of physiology by Burdach, and above all by Blumenbach, and the majority have no more than an anecdotal value, for they are not only related without any adequate guarantee, but even without the details indispensable to criticism.
As far back as the eighteenth century the great philosopher Kant, and in our own day the anatomist Wilhelm His, gave their verdict decidedly against such allegations, and absolutely denied any inheritance of mutilations; and now, after a decade or more of lively debate over the pros and cons, combined with detailed anatomical investigations, careful testing of individual cases, and experiment, we are in a position to give a decided negative and say there is no inheritance of mutilations.
Let me briefly explain how this result has been reached.
In the first place, the assertion that congenital stump-tails in dogs and cats depended on inherited mutilation proved to be unfounded. In none of the cases of stump-tails brought forward could it even be proved that the tail of the relevant parent had been torn or cut off, much less that the occurrence, in parents or grandparents, of short tails from internal causes was excluded. At the same time anatomical investigation of such stump-tails as occur in cats in the Isle of Man, and in many Japanese cats, and are frequently found in the most diverse breeds of dogs, showed that these had, in their structure, nothing in common with the remains of a tail that had been cut off, but were spontaneous degenerations of the whole tail, and are thus deformed tails, not shortened ones (Bonnet).
Experiments on mice also showed that the cutting off of the tail, even when performed on both parents, does not bring about the slightest diminution in the length of tail in the descendants. I have myself instituted experiments of this kind, and carried them out through twenty-two successive generations, without any positive result. Corroborative results of these experiments on mice have been communicated by Ritzema Bos and, independently, by Rosenthal, and a corresponding series of experiments on rats, which these two investigators carried out, yielded the same negative results.
When we remember that all the cases which have been brought forward in support of an inheritance of mutilations refer to a single injury to one parent, while, in the experiments, the same mutilation was inflicted on both parents through numerous generations, we must regard these experiments as a proof that all earlier statements were based either on a fallacy or on fortuitous coincidence. This conclusion is confirmed by all that we know otherwise of the effects of oft-repeated mutilations, as for instance the well-known mutilations and distortions which many peoples have practised for long, sometimes inconceivably long, ages on their children, especially circumcision, the breaking of the incisors, the boring of holes in lip, ear, or nose, and so forth. No child of any of these races has ever been brought into the world with one of these marks: they have to be re-impressed on every generation.
The experience of breeders agrees with this, and they therefore, as Wilckens remarks, have long regarded the non-inheritance of mutilations as an established fact. Thus there are breeds of sheep in which, for purely practical reasons, the tails have been curtailed quite regularly for about a century (Kühn); but no sheep with a stump-tail has ever been born in this breed. This is all the more important because there are other breeds of sheep (fat-rumped sheep) in which the lack of the tail is a breed character; it is thus not the case that there is anything in the intrinsic nature of the tail of the sheep to prevent it becoming rudimentary. The artificially rounded ear of fox-terriers, too, though cut for generations, never occurs hereditarily. Mr. Postans of Eastbourne informs me that the cocks which are to be used for cock-fighting are docked of their combs and wattles beforehand, and that this had been done for at least a century, but that no fighting cock without comb and wattles has been reared. In the same way various breeds of dog, such as the spaniels, have had their tails cut to half their length regularly and in both sexes for more than a century, yet in this case there is no hereditary diminution of the length of tail. Deformed stump-tails do indeed occur in most breeds of dog, but, as I said before, their anatomical character is quite different from that of artificially shortened tails, moreover they may occur in breeds whose tails have not suffered from the fashion of docking, as, for instance, in the Dachshund.
We may therefore affirm that an inheritance of artificially produced defects and mutilations is quite unproved, and in no way bears out the supposed inheritance of functional changes.
This is now admitted by the great majority of the adherents of the Lamarckian principle, and we may now regard this kind of 'proof' as disposed of.
In addition to the above, various sets of facts have been brought forward as proofs, and in particular the much discussed experiments of Brown-Séquard on guinea-pigs, from which it was inferred that epilepsy artificially induced could be transmitted. But these experiments do not really prove anything in regard to the question at issue, because epileptic-like convulsions may have very various causes, and these are, for the most part, quite unknown. Since artificial epilepsy can be induced in guinea-pigs by the most diverse injuries to the central or peripheral parts of the nervous system, this of itself points to the fact that it is not a question of the mere lesion of anatomical structure, I mean, of the breaking of the continuity of a definite part, and of its transmission. The result would, in any case, differ according to whether certain centres of the brain, or half the spinal cord, or the main nerve-trunks were cut through. There must, therefore, be something more needed to produce the appearance of epilepsy—some morbid process which may arise at different parts of the nervous system, and be continued from them to the brain-centres. This is corroborated by the fact that it takes at least fourteen days, and often from six to eight weeks, for epilepsy to develop after the operation, and that in many cases it does not develop at all. I have made the suggestion that, during or after the operation, some kind of pathogenic micro-organism might easily reach the wounded parts, and there excite inflammation, which may extend centripetally to the brain. Similar processes have been observed in connexion with lymph-vessels, and why should they not occur in connexion with nerves?