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Show 6 CHANGES IN ANIMALS AND PLANTS (Ch. I. What nature brings about in a great lapse of time we'occasion suddenly by changing the circumstances in which a species has been accustomed to live. All are aware that vegetables taken from their birth-place and cultivated in gardens, undergo changes which render them no longer recogni~able as the same plants. Many which were naturally hairy become smooth or nearly so; a great number of such as were creepers and trailed along the ground, rear their stalks and grow erect. Others lose their thorns or asperities ; others again, from the ligneous state which their stem possessed in hot ~limates' where they were indigenous, pass to the herbaceous, and, among them, some which were perennials become mere annuals. So well do botanists know the effects of such changes of circumstances, that they are averse to describe species from garden specimens, unless they are sure that they have been cultivated for a very short period. ' Is not the cultivated wheat,' (Triticum sativum) asks Lamarck, ' a vegetable brought by man into the state in which ' we now see it? Let any one tell me in what country a similar ' plant grows wild, unless where it has escaped from cultivated ' fields ? 'Vhere do we find in nature our cabbages, lettuces, ' ancl other culinary vegetables, in the state in which they . ' appear in our gardens ? Is it not the same in regard to ' a great quantity of animals which domesticity has changed ' or considerably modified* 1' Our domestic fowls and pigeons are unlike any wild birds. Our domestic ducks and geese have lost the faculty of raising themselves into the higher regions of the air, and crossin.Q' extensive countries in their fliO'ht .._. 0 ' like the wild ducks and wild geese from which they were originally derived. A bird which we breed in a cage cannot, when restored to liberty, fly like others of the same species which have been always free. This small alteration of circumstances, however, has only diminished the power of flight, without modifying the form of any part of the wings. But when individuals of the same race are retained in captivity "' Phil, Zool. tom. i. p. 227. Ch. I.] CAUSED BY DOMESTICATION, 7 during a considerable length of time, the form even of their parts is gradually made to differ, especially if climate, nourishment, and other circumstances, be also altered. The numerous races of dogs which we have produced by domesticity are nowhere to be found in a wild state. In nature we should seek in vain for mastiffs, harriers, spaniels, greyhounds, and other races, between which the differences are sometimes so great, that they would be readily admitted as specific between wild a~imals ; ' yet all these have sprung ' originally from a single race, at first approaching very near ' to a wolf, if, indeed, the wolf be not the true type which at ' some period or other was domesticated by man.' Although important changes in the nature of the places which they inhabit modify the organization of animals as well as vegetables, yet the former, says Lamarck, require more time to complete a considerable degree of transmutation, and, consequently, we are less sensible of such occurrences. Next to a diversity of the medium in which animals or plants may live, the circumstances which have most influence in modifying their organs are differences in exposure, climate, the nature of the soil, and other local particulars. These circumstances are as varied as are the characters of species, and, like them, pass by insensible shades into each other, there being every intermediate gradation between the opposite extremes. But each locality remains for a very long time the same, and is altered so slowly that we can only become conscious of the reality of the change, by consulting geological monuments, by which we learn that the order of things which now reigns in each place has not always prevailed, and by inference anticipate that it will not always continue the same •. Every considerable alteration in the local circumstances in which each race of animals exists, causes a change in their wants, and these new wants excite them to new actions and habits. These actions require the more frequent employment of some parts before but slightly exercised, and then greater develop· • Phil. Zool. tom. i. p. 232. |
