September 12, 1901J 



NA TURE 



Doubtful Causes of Variation. 

 Having indicated how maturity of the soma and of the germ- 

 cells, and how bodily welfare and interbreeding may act as 

 causes of variation, and also how swamping of the new variations 

 may be checked, I shall now refer to certain supposed causes of 

 variation. 



Maternal Imfressions. 



I may begin with the widespread belief that the offspring are 

 capable of being influenced in form, colour, and temperament by 

 maternal impressions — the belief we associate with the skilful 

 shepherd who peeled wands and stuck them up before the fulsome 

 ewes. MuUer (" Elements of Physiology," vol. ii. p. 1405) more 

 than half a century ago, conclusively argued against the belief 

 in maternal impressions, but the belief still prevails. I know of 

 two able naturalists who subscribe to the maternal impression 

 doctrine, and it is firmly held by many breeders and by not a 

 few physicians. A writer in a recent number of a quarterly 

 (Bibhy's Quarterly, Autumn Number, 1900, p. 163), which 

 circulates widely amongst farmers and stock-keepers, boldly 

 asserts that the existence of impressions which affect progeny 

 (more especially in colour) is a settled fact. This writer sup- 

 ports his case by referring to a highly successful breeder of 

 polled Angus cattle, who considered it necessary to surround 

 his herd "with a tight black fence in order to keep the females 

 from dropping red calves because they saw the red herds of his 

 neighbours." Reference is also made by this writer to the 

 belief, common in certain parts of England, that whitewashed 

 byres, regardless of the colour of the parents, produce light- 

 coloured calves ; that the colour of foals is often more influenced 

 by the stable companion of the dam than by her own colour or 

 that of the sire ; and that even the colour of birds varies with 

 the immediate surroundings, fmvls, e.g., however carefully 

 penned, hatching birds resembling in colour the hens 

 they habitually see in a neighbouring run. If maternal 

 impressions thus influence the offspring they must be 

 one of the most effective causes of variation. During the 

 last six years I have bred many hundreds of animals, but the 

 nearest approach to an instance of maternal impressions was a 

 dark pup with a white ring half round the neck, which sug- 

 gested the white metal collar sometimes worn by his sire. But 

 similar rings round the legs and tail rather discredited the view 

 that the white neck-ring was in any way related to the sire's 

 nickel-plated collar. Telegony was sometimes said to be due 

 to maternal impressions. It was doubtless for this reason that 

 I was urged some years ago to carefully prevent the mares used 

 in my experiments from seeing too much of the zebras. But 

 though numerous foals have been bred from mares stabled with 

 zebras or grazing with richly striped zebra hybrids, not a par- 

 ticle of evidence have I found in support of the maternal im- 

 pression doctrine. The foals have neither stripes nor upright 

 manes, and do not even attempt to mock the weird barking call 

 of the zebra. Sheep and cattle, goats, rabbits and guinea-pigs, 

 fowls and pigeons, have simply confirmed the results obtained 

 with horses. This being the case, grooms may very well omit 

 following the practice (considered so essential in Spain during 

 the Middle Ages, and still often religiously observed in England 

 and America) of setting " before the mares . . . the most goodly 

 beasts " by way of hinting to them the kind of foals they are 

 expected to produce. 



The Needs oj the Organism as a Cause of Variation, 



No recent biologists are perhaps prepared to believe like 

 Lamarck that the wings of birds were developed by their remote 

 ancestors making efforts to fly ; that by stretching its toes the 

 otter acquired webbed feet ; nor are they prepared to find in our 

 new mammal, the Ocapi, evidence in support of Lamarck's con- 

 tention that to meet new needs the giraffe by much stretching 

 gradually lengthened his neck. Vet it is difficult sometimes to 

 see any real difference between the beliefs of the new Lamarckians 

 and the old. It is maintained, for example, " that when a cer- 

 tain functional activity produces a certain change in one genera- 

 tion it will produce it more easily the next," that, e.g., flounders 

 and their allies by constant efforts generation after generation 

 have dragged the left eye to the right side, while by similar 

 efforts in the turbot and certain other flat fishes the right eye 

 has been shifted to the left side. It is not alleged bv Neo- 

 Lamarckians that globe fishes resulted from round fishes blowing 

 themselves out, or that flounders resulted from round fishes 

 generation after generation making eftbrts to flatten themselves. 



NO. 1663, VOL. 64] 



If by germinal variation and selection flounders were evolved 

 out of round fishes, is it not straining at a gnat and swallowing 

 a camel to refuse to admit that by the same factors the left eye 

 of the flounder has been transferred from the left to the right 

 side of the head ? In the flat fishes it is not difficult to imaging 

 how by variation and selection the eyes originally acquired the 

 power of responding to certain external stimuli. 



The Direct Action of the Environment and Use-Inheritance as 

 Causes of Variation. 

 Of the doctrine of the transmission of acquired characters, 

 still so often the subject of discussion, I need say little more 

 than that I have failed to discover any evidence in its favour. 

 Writing in 1S76, Darwin says, " In my opinion the greatest 

 error which I have committed has been not allowing sufficient 

 weight to the direct action of the environment, i.e., food, 

 climate, &c., independently of natural selection" (" Life and 

 Letters " : Letter to Moritz Wagner). Darwin not only in his 

 later years reverted to the teaching of Bufton, but in as far as he 

 continued to believe in the " inherited efiects of use and disuse" 

 he adopted the views of Erasmus Darwin and Lamarck. While 

 admitting that the direct action of the environment on the soma 

 and use-inheritance are indirect— it may be potent — causes of 

 variation, I do not believe there is any trustworthy evidence in 

 support of the view that definite somatic variations are ever 

 transmitted. 



Telegony as a Cause of Variation. 



The belief in telegony rs less deserving of consideration than 

 the doctrine of the transmission of acquired characters. Never- 

 theless I perhaps ought to refer to it at greater length, not so 

 much because of its scientific importance, but because it interests 

 all sorts and conditions of men in many different parts of the 

 world. Telegony ("infection of the germ" of older writers) 

 means that not only the immediate parents but also the previous 

 mates (if any) contribute to the characters of the offspring ; that, 

 e.g., a mare which had produced foals to, say, " Ladas " and 

 " Persimmon " might thereafter give birth to a foal by " Flying 

 Fox," to which "Ladas" and "Persimmon," as well as the 

 actual sire, contributed some of their characteristics. Many even 

 think a sire may transmit definite structural characters from one 

 mate to another. If there issucha thingastelegony, if it is possible 

 to blend without the risks of intercrossing the characteristics of 

 several individuals or varieties, progressive development would be 

 greatly accelerated. Though the doctrine of "infection" has 

 probably long formed part of the breeder's creed, it received but 

 little attention from men of science until in 1820 Lord Morton 

 communicated a case of infection to the Royal Society, which in 

 due time was published in the Philosophical Transactions. In 

 this the most credible and best authenticated of all the cases of 

 telegony on record a chestnut mare, after rearing a quagga 

 hybrid, produced to a black Arabian horse three foals of a 

 peculiar bay colour, one of them (a filly) showing more stripes 

 than the quagga hybrid, and, according to the stud groom in 

 charge of " the colts," characterised by a mane "which from 

 the first was short, stiff, and upright " {Phil. Trans., 1820, p. 21). 

 Darwin, after fully considering Lord Morton's case, came to 

 the conclusion that the chestnut mare had been infected, 

 and this case along with others led him to believe that the 

 first male influenced " the progeny subsequently borne by the 

 mother to other males " (" Animals and Plants," vol. ii, pp. 435, 

 436.) If the upright zebra-like mane in one of the pure-bred 

 colts and the markings on all three were the result of the 

 chestnut mare having been first mated with a quagga, there is 

 undoubtedly such a thing as telegony, and the presumption is 

 that other mares first mated with a quagga or zebra and then 

 with a black Arabian would give birth to striped offspring with 

 a stiff if not quite upright mane. The evidence that from the 

 first the mane of the filly was short, stiff, and upright is most 

 unsatisfactory. It consists of an allegation by a stud groom. 

 That the mane was upright, as in the quagga and zebra, is 

 a priori imftohahXt (l) because the mane of the quagga hybrid 

 instead of being short and stiff was long and lank enough to 

 arch to one side of the neck ; (2) because the mane of zebra 

 hybrids throughout the greater part of the year is so long that it 

 falls to one or it may be both sides of the neck ; and (3) because in 

 the EquidK an upright mane is always accompanied by a tail de- 

 ficient of hairs at the root — in the filly the tail is as perfect as that 

 of her Arab sire. We have still stronger evidence that the allega- 

 tion of the groom was unfounded from drawings (of the chestnut 

 mare, her three "colts," the black Arab, the quagga, and the 



