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Show 28G DEFINITE ACTION OF 'IIIE CHAP. XXIII. importance than the conditions to which it bas been exposed. It seems, indeed, to be a general rule that conspicuous variations occm· rarely, and in one individual alone out of many thousands, though all may have been exposed, as far as we can judge, to nearly the same conditions. As the most strongly marked variations graduate insensibly into the most trifling, we are led by the same train of thought to attribute each slight variation much more to innate differences of constitution, however caused, than to the definite action of the surrounding conditions. We are led to the same conclusion by considering the cases, formerly alluded to, of fowls and pigeons, which have varied and will no doubt go on varying in directly opposite ways, though kept clming many generations under nearly the same conditions. Some, for instance, arc born with their beaks, wings, tails, legs, &c., a little longer, and others with these same parts a little shorter. By tho long-continued selection of such slight individual differences, which occm in birds kept in tho same aviary, widely different races could certainly be formed; and long-continued selection, important as is the result, does nothing but preserve the variations which appear to us to arise spontaneously. In these cases we sec that domesticated animals vary in an indefinite number of particulars, though treated as uniformly as is possible. On the other hand, there arc instances of animals and plants, which, though exposed to very different conditions, both lmdcr natm·e and domestication, have varied in nearly the same manner. Mr. Layard informs me that he has observed amongst the Caffrcs of South Africa a dog singularly like an arctic Esquimaux clog. Pigeons in India present nearly the same wide diversities of colour as in Europe; and I have seen chequered and simply barred pigeons, and pigeons with blue and white loins, from Sierra Leone Madeira, England, and India. New varieties of flowers are continuau; raised in different parts of Great Britain, but many of these arc found by the judges at our exhibitions to be almost identical with old varieties. A vast number of now fruit-trees and culinary veget..'tblcs have been produced in North America: these differ from Emopean varieties in the same geneml manner as the several varieties raised in Europe differ from each other; and no one has ever pretended that the climate of America has given to the many American varieties any geneml character by which they can be recognised. Nevertheless, from the facts previously advanced on the authority of Mr. Meehan with respect to American and European forest-trees, it would be rash to affirm that varieties raised in the two countries would not in the course of ages assume a distinctive character. Mr. Masters has recorded a striking fact 56 bearing on this subject: he raised numerous plants of Hybiscus f:Jyriacus from seed collected in South Carolina and the Holy Land, where the parent-plants must have been exposed to considerably different conditions ; yet the seedlings from both localities broke into two similar strains, one with obtuse leaves and pmple or crimson flowers, and the other with elongated leaves and more or less pink flowers. 56 'Gardener's Chronicle,' 1857, p. 629. CrrAP. XXIII. CONDITIONS OF LIFE. 287 We may, also, infer tho prepotent influe~c.e of the. constitution of the oro·anism over the definite action of the conditwns of life, from tho several ca~es given in the earlier chapters of parallel series of varieties,-:-a~ important subject, hereafter to be more fully discussed. Sub-vanetles of tho several kinds of wheat, gourds, poaches, and other plants, and to a certain limited extent sub-varieties of the fowl, pigeon, and dog, have boon shown either to resemble or to differ from each other in a closely corresponding and parallel manner. In other cases, a variety of one species resembles a distinct species; or the varieties of two distinct species resemble each other. Although these parallel resemblances no doubt often result from reversion to the former characters of a common progenitor ; yet in other cases, when new characters first appear, the resemblance must be attributed to tho inheritance of a similar constitution, and consequently to a tendency to vary in the same manner. We see something o! a s~milar kind D: the same monstrosity appearing and reappearing many tunes m the same arnmal, and, as Dr. Maxwell Masters has remarked to me, in the same plant. vVe may at least conclude thus far, that the amount of modification which animals and plants have undergone under domestication, does not correspond with the degree to which they have been subjected to changed circumstanc~s. As we know tho parentage of domesticated bli·ds far better than of most quadrupeds, we will glance through the list. The pigeon has varied in Europe more than almost any other bird; yet it is a native species, and has not been exposed to any extraordinary chanae of conditions. rrhe fowl has varied equally, or almost equally, with the pigeon, and is a native of the hot jungles of India. Neither the peacock, a native of the same country, nor tho guinea-fowl, an inhabitant of the ill·y deserts of Africa, has varied at all, or only in colour. 1'he' turkey, from Mexico, has varied but little. rrhe cluck, on the other hand, a native of Europe, has yielded some well-marked races; and as this is an aquatic bird, it must have been subjected to a far more serious change in its habits than the pigeon or even the fowl, which 11evortheless have varied in a much higher degree. The goose, a native of Europe and aquatic like the duck, has varied less than any other domesticated bird, except the peacock. Bud-variation is, also, important under our present point of view. In some few cases, as when all the eyes or buds on the same tuber of the potato, or all the fruit on the same p1umtt ·ee, or all the flowers on the same plant, have suddenly varied in the same manner, it might be argued that the varia- |