Problems of Genetics

by William Bateson

I do not doubt that evidence of this type will be greatly extended. As a contribution to genetic physiology these facts are very important and interesting, but I cannot think that any one, on reflexion, will feel encouraged by such indications to revive old beliefs in the direct origin of adaptations.

In these respects we are simply left where we were. The force of objections based upon the existence of adaptative mechanisms is no greater than it has always been. On the contrary the fact that variations can now so generally be recognized as definite is some alleviation of the difficulty. We can moreover disabuse ourselves of the notion that for all characters which are definite or fixed, some utilitarian rationale may be presumed. Upon that point the study of variation has provided a perfectly clear answer.

In frankly recognizing that the fixity of characters in general need not connote usefulness to their possessors we deliver ourselves of a distracting pre-occupation and prepare our minds for an investigation of the properties of living organisms in the same spirit as that in which the chemist and the physicist examine the properties of unorganized materials. The creature persists not merely by virtue of its characteristics but in spite of them, and the fact of its persistence proves no more than that on the whole the balance of its properties leaves something in its favour.

It may be noted by the way that the fact that the structures of living things are on the whole adaptative was not always obvious. Though to naturalists of this generation it is a truism, we have only to turn to Buffon to find that in his philosophy of nature it played no essential part. The passage in which Buffon describes what he regards as the forlorn and degraded condition of the Woodpecker is well known. We have come to think of the Woodpecker as a capital example of adaptation to the mode of life; but Buffon after enumerating the hard features of the bird's existence, forced to earn its living by piercing the bark of trees in an attitude of perpetual constraint, remarks[1] "Tel est l'instinct étroit et grossier d'un oiseau borné a une vie triste et chétive. Il a reçu de la Nature des organes et des instrumens appropriés a cette destinée ou plutôt il tient cette destinée même des organes avec lesquels il est né" (my italics). His reflexions on the Stilt (Himantopus) read even more strangely to us, accustomed as we are to see in the prodigious length and thinness of the shanks and in the other features of its organisation palpable adaptations to a wading life. For Buffon, however, this curious bird seemed a poor, neglected production, extravagant in its disproportions, one of the misfits of creation, left as a shadow in the picture composed of nature's more successful efforts.[2] This theme he develops at some length, being evidently well pleased with the idea.

Our way of regarding these things is doubtless sounder and more fruitful than Buffon's, but it is well to remember that what seems so obvious to us looked quite differently to other excellent observers; and stupid as it may have been to have overlooked plain examples of adaptation, it is a far worse mistake to see adaptation everywhere. I do not seek to minimise the real and permanent difficulty which the existence of adaptations creates, but by the suggestion that all normal specific differences are adaptational that difficulty was quite gratuitously increased.

In these respects it may be claimed that progress has been made, even if that progress seem outwardly of small account.

But all constructive theories of evolution have been built on the understanding that what we know of the relation of varieties to species justifies the assumption that the one phenomenon is a phase of the other, and that each species arises or has arisen from another species either by one or several genetic steps. In the varieties we have accustomed ourselves to think that we see those steps. We still know little enough of the mode of occurrence of variation, but we do begin to know something, and if we ask ourselves whether our knowledge, such as it is, conforms at all readily with our former expectations, we cannot with any confidence assert that it does. Among the plants and animals genetically investigated are many illustrations of very striking and distinct varieties. Many of these might readily enough be accepted as species by even the most exacting systematists, and not a few have been so treated in classification; but when we have examined their relationship to each other we feel not merely that they are not species in any strict sense but that the distinctions they present cannot be regarded as stages in the direction of specific difference. Complete fertility of the results of inter-crossing is and I think must rightly be regarded as inconsistent with actual specific difference; and of variations leading to that consequence no clear indication has yet been found. As an example of possible exceptions mention should perhaps be made of the case of a giant form of Primula sinensis investigated by Keeble.[3] It arose from a "Star" Primula of normal size, and though fertile with its own pollen all attempts to fertilise it with the pollen of other forms failed. Miss Pellew, who did these fertilisations, tells me that very extensive trials were made, and repeated in several seasons. Ultimately two plants were raised from it fertilised with a plant of the strain from which it sprang, and these proved sterile. In the light of modern experience the significance of such isolated instances is doubtful.

All the strains known as "Giants" are, as Messrs. Sutton have always found, more or less sterile, and their sterility is presumably due to some negative defect.

In regard to the fertility of Primula species there are several paradoxes. For example the long-styled varieties, apart from giants, are fertile with their own pollen, and for many years short-styled plants have not been used in most strains. Auriculas and Polyanthuses, on the contrary, are generally if not always bred from short-styled plants, as the florists have decided that the long-styled are inadmissible. Mr. R. P. Gregory tells me that, though most strains of P. sinensis give seed enough when only long-styled plants are used, he finds nevertheless that when a "legitimate" union is made the amount of seed usually increases much as Darwin observed. Darwin's statement that plants of "illegitimate" origin are less fertile than the "legitimately" raised plants is also in general confirmed by his experience. To this rule there were some marked exceptions in strains derived from long-styled plants, which though illegitimate showed a high degree of fertility, but illegitimate unions between short-styled plants always produced comparatively sterile offspring. I have no records of the behavior of Auriculas and Polyanthuses. It would be interesting to know whether among them pure strains of short-styled plants (dominants) have appeared, and, if so, how their fertility is affected. Without much more critical data I suppose no one would nowadays be inclined to follow Darwin in instituting a comparison between the sterility of hybrids and that of illegitimately raised plants of heterostyle species.[4] It is even difficult to imagine any essential resemblance between these two phenomena, nor has evidence ever been produced to show that illegitimately raised plants have bad pollen grains, which is the usual symptom of sterility in hybrid plants and the consequence, as we believe, of failure of some essential division in the process of maturation.

The difficulty that we have no knowledge of the contemporary origin of forms, from a common stock, which when crossed together give a sterile product, is one of the objections constantly and prominently adduced from the time of the first promulgation of evolutionary ideas. In the light of recent work the objection has gathered strength. Why, if we are able to produce instances of variation colourably simulating specific difference in almost all other respects, do we never find an original appearance of this most widely spread of all specific characteristics? No doubt all breeders know that sterile animals and plants occasionally appear in their cultures, but it is more in accordance with probability that the sterility in these sporadic instances should be regarded as due to defect than that it should be thought comparable with that of the sterile hybrids. For their sterility must, by all analogy with results elsewhere seen, be attributed not to the absence of something, but to the presence and operation of complementary factors leading to the production of inhibition of division; and consistently with that interpretation, we find that when from a partially sterile hybrid comparatively fertile offspring can be raised, their comparative fertility continues in the posterity generally if not always without diminution. The distinction between these several kinds of sterility was of course not understood in Darwin's time. The comparison, for example, which he instituted[5] between the sterility of "contabescent" anthers and that of hybrids no longer holds, for at least in those cases in which the nature of contabescent anthers have been genetically investigated (Sweet Pea, Tropaeolum) they proved to be a simple recessive character. Nor can we now easily suppose that the attempt there made by Darwin to suggest resemblance between the sterility produced by unnatural conditions and that of hybrids has any physiological justification.