Problems of Genetics

by William Bateson

No epitome of the older evidence for the inheritance of adaptative changes is here required. That has often been collected, especially by Weismann, who exposed its weaknesses so thoroughly as to carry conviction to most minds, and showed that whether the phenomenon occurs or not, no one can yet prove that it does. Belief in these transmissions, after being almost universally held, was with singular unanimity abandoned. This change in opinion, though doing credit to the faith of the scientific community in evidential reasoning, is the more remarkable inasmuch as the strength of the idea was not derived from the minute amounts of supposed facts now demolished. On the contrary, it was really an instinctive deduction from a wide superficial acquaintance with the properties of animals and plants. They can accommodate themselves to circumstances. They do make responses sometimes marvellously appropriate to demands for which they can scarcely have been prepared. What more natural than to suppose that the permanent adaptations have been achieved by inherited summation of such responses? No one had actually been driven to believe in the inheritance of adaptative changes because bitches which had been docked had been known to give birth to tailless puppies, or because certain wheat in Norway was alleged to have become acclimatized in a few generations. Evidence of this kind was collected and produced rather as an ornamental appendix to a proposition already accepted, and held to be plainly demonstrated by the facts of nature. Looked at indeed in that preliminary and uncritical way, the case is simply overwhelming. Those who desire to see how strong it is should turn to Samuel Butler's Life and Habit, and even if in reading they reiterate to themselves that no experimental evidence exists in support of the propositions advanced, the misgiving that none the less they may be true is likely to remain. Making every deduction for the fact that the wonders of adaptation have been grossly exaggerated, and that marvels of fitness and correspondence between means and ends have grown out of mere anthropomorphic speculations, there is much more left to be accounted for than can at all comfortably be accepted as the product of happy accidents. So oppressive are these difficulties that we can scarcely blame those who imagine that the study of heredity is primarily directed to the problem of the transmission of acquired characters, a preconception still almost universal among the laity.

But since the belief in transmission of acquired adaptations arose from preconception rather than from evidence, it is worth observing that, rightly considered, the probability should surely be the other way. For the adaptations relate to every variety of exigency. To supply themselves with food, to find it, to seize and digest it, to protect themselves from predatory enemies whether by offence or defence, to counter-balance the changes of temperature, or pressure, to provide for mechanical strains, to obtain immunity from poison and from invading organisms, to bring the sexual elements into contact, to ensure the distribution of the type; all these and many more are accomplished by organisms in a thousand most diverse and alternative methods. Those are the things that are hard to imagine as produced by any concatenation of natural events; but the suggestions that organisms had had from the beginning innate in them a power of modifying themselves, their organs and their instincts so as to meet these multifarious requirements does not materially differ from the more overt appeals to supernatural intervention.

The conception, originally introduced by Hering and independently by S. Butler, that adaptation is a consequence or product of accumulated memory was of late revived by Semon and has been received with some approval, especially by F. Darwin. I see nothing fantastic in the notion that memory may be unconsciously preserved with the same continuity that the protoplasmic basis of life possesses. That idea, though purely speculative and, as yet, incapable of proof or disproof contains nothing which our experience of matter or of life at all refutes. On the contrary, we probably do well to retain the suggestion as a clue that may some day be of service. But if adaptation is to be the product of these accumulated experiences, they must in some way be translated into terms of physiological and structural change, a process frankly inconceivable.

To attempt any representation of heredity as a product of memory is, moreover, to substitute the more obscure for the less. Both are now inscrutable; but while we may not unreasonably aspire to analyse heredity into simpler components by ordinary methods of research, the case of memory is altogether different. Memory is a mystery as deep as any that even psychology can propound. Philosophers might perhaps encourage themselves to attack the problem of the nature of memory by reflecting that after all the process may in some of its aspects be comparable with that of inheritance, but the student of genetics, as long as he can keep in close touch with a profitable basis of material fact, will scarcely be tempted to look for inspiration in psychical analogies.

For a summary of the recent evidence I may refer the reader to Semon's paper[1] where he will find a collection of these observations described from the standpoint of a convinced believer. At the outset one cannot help being struck by the fact that of the instances alleged, very few, even if authentic, show the transmission of acquired modifications which can in any sense be regarded as adaptative, and many are examples not so much of a transmission of characters produced in the parents as of variation induced in the offspring as a consequence of treatment to which the parents were submitted, the parents themselves remaining apparently unmodified. No one questions the great importance of evidence of this latter class as touching the problem of the causes of variation, but it is not obvious why it is introduced in support of the thesis that acquired characters are inherited.

It is most difficult to form a clear judgment of the value of the evidence as a whole. To doubt the validity of testimony put forward by reputable authors is to incur a charge of obstinacy or caprice; nevertheless in matters of this kind, where the alleged phenomena are, if genuine, of such exceptional significance, belief should only be extended to evidence after every possible source of doubt has been excluded. We believe such things when we must, but not before. At the very least we are entitled to require that confirmatory evidence should be forthcoming from independent witnesses. So far as I have seen, this requirement is satisfied in scarcely any of the examples that have been lately published, and until it is, judgment may reasonably be suspended.

In some cases, however, the facts are not doubtful. Standfuss, by subjecting pupae of Vanessa urticae to cold, produced the now well-known temperature-aberrations in which the dark pigment is greatly extended. He put together in a breeding-cage 32 males and 10 females showing this modification in various degrees. Two of these females died without leaving young. Seven produced exclusively normal offspring. From the eighth female 43 butterflies were bred, and of these there were four (all males) which to a greater or less extent exhibited the aberrational form.[2] The mother of this family was the most abnormal of the 10 females originally put in.

Fischer's experiment with Aretia caja was on similar lines. From pupae which had been frozen almost all the moths which emerged showed aberrational markings. A pair of these mated and produced 173 young which pupated. Those which emerged early were all normal, but of those which emerged late, 17 had in various degrees abnormal markings like those of the parents.[3] In neither of these examples is there any question as to the facts. Both observers have great experience and give full details of their work.

As regards Vanessa urticae, however, it must be recalled that Fischer himself showed that in Nymphalids somewhat similar aberrations could be produced both by heat and by cold, and even by centrifuging the pupae. Frl. von Linden produced a transitional form of the same aberration in V. urticae by the action of carbonic acid gas.[4] It is highly probable that the appearance is due to a morbid change, perhaps an arrest of development, which may be brought about by a great diversity of causes. In the experiments the cause probably was a diseased condition of the tissues of the mother herself. She had been subjected to freezing sufficiently severe to prevent the proper development of the pigments and some of the ovarian cells presumably suffered also. It will be observed that the only specimens which were affected were the offspring of the most abnormal female, and of them only four out of forty-three showed any change.

The same interpretation probably applies to the cases in Arctia caja. In this species the markings are well known to be liable to great variation. As Barrett says, even in nature individuals are rarely quite alike, and an immense number of strange forms occur in collections.[5] These are greatly sought after by some collectors, especially in England, where they fetch high prices at auctions, and it is notorious that most of them come from Lancashire and the West Riding of Yorkshire. It is commonly supposed that the breeders of that district subject them to abnormal conditions, and especially to unnatural feeding, but I know no clear evidence that this is true. From whatever cause it is certain that the natural pattern is, in some strains at all events, very easily disturbed.