CAMBRIDGE UNIVERSITY PRESS London: FETTER LANE, E.C. C. F. CLAY, Manager Edinburgh: 100, PRINCES STREET ALSO London: H. K. LEWIS, 136, GOWER STREET, W.C. Berlin: A. ASHER AND CO. Leipzig: F. A. BROCKHAUS New York: G. P. PUTNAM’S SONS Bombay and Calcutta: MACMILLAN AND Co., Ltd. All rights reserved Edited by his son FRANCIS DARWIN Honorary Fellow of Christ's College Cambridge: at the University Press 1909 Astronomers might formerly have said that God ordered each planet to move in its particular

We know from the contents of Charles Darwin’s Note Book of 1837 that he was at that time a convinced Evolutionist {1} . Nor can there be any doubt that, when he started on board the Beagle , such opinions as he had were on the side of immutability. When therefore did the current of his thoughts begin to set in the direction of Evolution? We have first to consider the factors that made for such a change. On his departure in 1831, Henslow gave him vol. I. of Lyell's Principles , then just publishe

An individual organism placed under new conditions [ often ] sometimes varies in a small degree and in very trifling respects such as stature, fatness, sometimes colour, health, habits in animals and probably disposition. Also habits of life develope certain parts. Disuse atrophies. [ Most of these slight variations tend to become hereditary. ] When the individual is multiplied for long periods by buds the variation is yet small, though greater and occasionally a single bud or individual departs

I may premise, that according to the view ordinarily received, the myriads of organisms peopling this world have been created by so many distinct acts of creation. As we know nothing of the « illegible » will of a Creator,—we can see no reason why there should exist any relation between the organisms thus created; or again, they might be created according to any scheme. But it would be marvellous if this scheme should be the same as would result from the descent of groups of organisms from [ cer

The most favourable conditions for variation seem to be when organic beings are bred for many generations under domestication {186} : one may infer this from the simple fact of the vast number of races and breeds of almost every plant and animal, which has long been domesticated. Under certain conditions organic beings even during their individual lives become slightly altered from their usual form, size, or other characters: and many of the peculiarities thus acquired are transmitted to their o

Having treated of variation under domestication, we now come to it in a state of nature . Most organic beings in a state of nature vary exceedingly little {218} : I put out of the case variations (as stunted plants &c., and sea-shells in brackish water {219} ) which are directly the effect of external agencies and which we do not know are in the breed {220} , or are hereditary . The amount of hereditary variation is very difficult to ascertain, because naturalists (partly from the want o

I have as yet only alluded to the mental qualities which differ greatly in different species. Let me here premise that, as will be seen in the Second Part, there is no evidence and consequently no attempt to show that all existing organisms have descended from any one common parent-stock, but that only those have so descended which, in the language of naturalists, are clearly related to each other. Hence the facts and reasoning advanced in this chapter do not apply to the first origin of the sen

I must here premise that, according to the view ordinarily received, the myriads of organisms, which have during past and present times peopled this world, have been created by so many distinct acts of creation. It is impossible to reason concerning the will of the Creator, and therefore, according to this view, we can see no cause why or why not the individual organism should have been created on any fixed scheme. That all the organisms of this world have been produced on a scheme is certain fr

In the Tertiary system, in the last uplifted beds, we find all the species recent and living in the immediate vicinity; in rather older beds we find only recent species, but some not living in the immediate vicinity {327} ; we then find beds with two or three or a few more extinct or very rare species; then considerably more extinct species, but with gaps in the regular increase; and finally we have beds with only two or three or not one living species. Most geologists believe that the gaps in t

For convenience sake I shall divide this chapter into three sections {340} . In the first place I shall endeavour to state the laws of the distribution of existing beings, as far as our present object is concerned; in the second, that of extinct; and in the third section I shall consider how far these laws accord with the theory of allied species having a common descent. In the following discussion I shall chiefly refer to terrestrial mammifers, inasmuch as they are better known; their differenc

It has been observed from the earliest times that organic beings fall into groups {426} , and these groups into others of several values, such as species into genera, and then into sub-families, into families, orders, &c. The same fact holds with those beings which no longer exist. Groups of species seem to follow the same laws in their appearance and extinction {427} , as do the individuals of any one species: we have reason to believe that, first, a few species appear, that their numbe

Scarcely anything is more wonderful or has been oftener insisted on than that the organic beings in each great class, though living in the most distant climes and at periods immensely remote, though fitted to widely different ends in the economy of nature, yet all in their internal structure evince an obvious uniformity. What, for instance, is more wonderful than that the hand to clasp, the foot or hoof to walk, the bat’s wing to fly, the porpoise’s fin {455} to swim, should all be built on the

Parts of structure are said to be “abortive,” or when in a still lower state of development “rudimentary {486} ,” when the same reasoning power, which convinces us that in some cases similar parts are beautifully adapted to certain ends, declares that in others they are absolutely useless. Thus the rhinoceros, the whale {487} , etc., have, when young, small but properly formed teeth, which never protrude from the jaws; certain bones, and even the entire extremities are represented by mere little

I will now recapitulate the course of this work, more fully with respect to the former parts, and briefly « as to » the latter. In the first chapter we have seen that most, if not all, organic beings, when taken by man out of their natural condition, and bred during several generations, vary; that is variation is partly due to the direct effect of the new external influences, and partly to the indirect effect on the reproductive system rendering the organization of the offspring in some degree p