"Taking the chain of life in the inverse order of nature—that is to say, from man downwards—we certainly perceive a sustained but irregular degradation of organism, with an increasing simplicity both in organism and faculties.
"This fact should throw light upon the order taken by nature, but it does not show us why the gradation is so irregular, nor why throughout its extent we find so many anomalies or digressions which have apparently no order at all in their manifold varieties.[272] The explanation of this must be sought for in the infinite diversity of circumstances under which organisms have been developed. On the one hand, there is a tendency to a regular progressive development; on the other, there is a host of widely different surroundings which tend continually to destroy the regularity of development.
"It is necessary to explain what is meant by such expressions as 'the effect of its environment upon the form and organization of an animal.' It must not be supposed that its surroundings directly effect any modification whatever in the form and organization of an animal.[273] Great changes in surroundings involve great changes in the wants of animals, and these changes in their wants involve corresponding changes in their actions. If these new wants become permanent, or of very long duration, the animals contract new habits, which last as long as the wants which gave rise to them.[274] A great change in surroundings, if it persist for a long time, must plainly, therefore, involve the contraction of new habits. These new habits in their turn involve a preference for the employment of such and such an organ over such and such another organ, and in certain cases the total disuse of an organ which is no longer wanted. This is perfectly self-evident.[275]
"On the one hand, new wants have rendered a part necessary, which part has accordingly been created by a succession of efforts: use has kept it in existence, gradually strengthening and developing it till in the end it attains a considerable degree of perfection. On the other, new circumstances having in some cases rendered such or such a part useless, disuse has led to its gradually ceasing to receive the development which the other parts attain to; on this it becomes reduced, and in time disappears.[276]
"Plants have neither actions nor habits properly so called, nevertheless they change in a changed environment as much as animals do. This is due to changes in nutrition, absorption and transpiration, to degrees of heat, light, and moisture, and to the preponderance over others which certain of the vital functions attain to."
Lamarck is led into the statement that plants have neither actions nor habits, by his theories about the nervous system and the brain. Plain matter-of-fact people will prefer the view taken by Buffon, Dr. Darwin, and, more recently, by Mr. Francis Darwin, that there is no radical difference between plants and animals.
"The differences between well-nourished and ill-nourished plants become little by little very noticeable. If individuals, whether animal or vegetable, are continually ill-fed and exposed to hardships for several generations, their organization becomes eventually modified, and the modification is transmitted until a race is formed which is quite distinct from those descendants of the common parent stock which have been placed in favourable circumstances.[277] In a dry spring the meagre and stunted herbage seeds early. When, on the other hand, the spring is warm but with occasional days of rain, there is an excellent hay-crop. If, however, any cause perpetuates unfavourable circumstances, plants will vary correspondingly, first in appearance and general conditions, and then in several particulars of their actual character, certain organs having received more development than others, these differences will in the course of time become hereditary.[278]
"Nature changes a plant or animal's surroundings gradually—man sometimes does so suddenly. All botanists know that plants vary so greatly under domestication that in time they become hardly recognizable. They undergo so much change that botanists do not at all like describing domesticated varieties. Wheat itself is an example. Where can wheat be found as a wild plant, unless it have escaped from some neighbouring cultivation? Where are our cauliflowers, our lettuces, to be found wild, with the same characters as they possess in our kitchen gardens?
"The same applies to our domesticated breeds of animals. What a variety of breeds has not man produced among fowls and pigeons, of which we can find no undomesticated examples!"[279]
The foregoing remarks on the effects of domestication seem to have been inspired by those given p. 123 and pp. 168, 169 of this volume.[280]