Читать книгу The Foundations of the Origin of Species - Чарльз Дарвин, Darwin Charles - Страница 2
PART I
§ I. «On Variation under Domestication, and on the Principles of Selection.»
ОглавлениеAn 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 widely from its type (example)36 and continues steadily to propagate, by buds, such new kind.
When the organism is bred for several generations under new or varying conditions, the variation is greater in amount and endless in kind [especially37 holds good when individuals have long been exposed to new conditions]. The nature of the external conditions tends to effect some definite change in all or greater part of offspring, – little food, small size – certain foods harmless &c. &c. organs affected and diseases – extent unknown. A certain degree of variation (Müller's twins)38 seems inevitable effect of process of reproduction. But more important is that simple «?» generation, especially under new conditions [when no crossing] «causes» infinite variation and not direct effect of external conditions, but only in as much as it affects the reproductive functions39. There seems to be no part (beau ideal of liver)40 of body, internal or external, or mind or habits, or instincts which does not vary in some small degree and [often] some «?» to a great amount.
[All such] variations [being congenital] or those very slowly acquired of all kinds [decidedly evince a tendency to become hereditary], when not so become simple variety, when it does a race. Each41 parent transmits its peculiarities, therefore if varieties allowed freely to cross, except by the chance of two characterized by same peculiarity happening to marry, such varieties will be constantly demolished42. All bisexual animals must cross, hermaphrodite plants do cross, it seems very possible that hermaphrodite animals do cross, – conclusion strengthened: ill effects of breeding in and in, good effects of crossing possibly analogous to good effects of change in condition «?»43.
Therefore if in any country or district all animals of one species be allowed freely to cross, any small tendency in them to vary will be constantly counteracted. Secondly reversion to parent form – analogue of vis medicatrix44. But if man selects, then new races rapidly formed, – of late years systematically followed, – in most ancient times often practically followed45. By such selection make race-horse, dray-horse – one cow good for tallow, another for eating &c. – one plant's good lay «illegible» in leaves another in fruit &c. &c.: the same plant to supply his wants at different times of year. By former means animals become adapted, as a direct effect to a cause, to external conditions, as size of body to amount of food. By this latter means they may also be so adapted, but further they may be adapted to ends and pursuits, which by no possibility can affect growth, as existence of tallow-chandler cannot tend to make fat. In such selected races, if not removed to new conditions, and «if» preserved from all cross, after several generations become very true, like each other and not varying. But man46 selects only «?» what is useful and curious – has bad judgment, is capricious, – grudges to destroy those that do not come up to his pattern, – has no [knowledge] power of selecting according to internal variations, – can hardly keep his conditions uniform, – [cannot] does not select those best adapted to the conditions under which «the» form «?» lives, but those most useful to him. This might all be otherwise.
36
Evidently a memorandum that an example should be given.
37
The importance of exposure to new conditions for several generations is insisted on in the Origin, Ed. i. p. 7, also p. 131. In the latter passage the author guards himself against the assumption that variations are “due to chance,” and speaks of “our ignorance of the cause of each particular variation.” These statements are not always remembered by his critics.
38
Cf. Origin, Ed. i. p. 10, vi. p. 9, “Young of the same litter, sometimes differ considerably from each other, though both the young and the parents, as Müller has remarked, have apparently been exposed to exactly the same conditions of life.”
39
This is paralleled by the conclusion in the Origin, Ed. i. p. 8, that “the most frequent cause of variability may be attributed to the male and female reproductive elements having been affected prior to the act of conception.”
40
The meaning seems to be that there must be some variability in the liver otherwise anatomists would not speak of the ‘beau ideal’ of that organ.
41
The position of the following passage is uncertain. “If individuals of two widely different varieties be allowed to cross, a third race will be formed – a most fertile source of the variation in domesticated animals. «In the Origin, Ed. i. p. 20 the author says that “the possibility of making distinct races by crossing has been greatly exaggerated.”» If freely allowed, the characters of pure parents will be lost, number of races thus «illegible» but differences «?» besides the «illegible». But if varieties differing in very slight respects be allowed to cross, such small variation will be destroyed, at least to our senses, – a variation [clearly] just to be distinguished by long legs will have offspring not to be so distinguished. Free crossing great agent in producing uniformity in any breed. Introduce tendency to revert to parent form.”
42
The swamping effect of intercrossing is referred to in the Origin, Ed. i. p. 103, vi. p. 126.
43
A discussion on the intercrossing of hermaphrodites in relation to Knight’s views occurs in the Origin, Ed. i. p. 96, vi. p. 119. The parallelism between crossing and changed conditions is briefly given in the Origin, Ed. i. p. 267, vi. p. 391, and was finally investigated in The Effects of Cross and Self-Fertilisation in the Vegetable Kingdom, 1876.
44
There is an article on the vis medicatrix in Brougham’s Dissertations, 1839, a copy of which is in the author’s library.
45
This is the classification of selection into methodical and unconscious given in the Origin, Ed. i. p. 33, vi. p. 38.
46
This passage, and a similar discussion on the power of the Creator (p. 6), correspond to the comparison between the selective capacities of man and nature, in the Origin, Ed. i. p. 83, vi. p. 102.
