The origin of species by means of natural selection, or, The preservation of favoured races in the struggle for life / by Charles Darwin.

  • Darwin, Charles, 1809-1882.
Date:
1880
Catalogue details

Licence: Public Domain Mark

Credit: The origin of species by means of natural selection, or, The preservation of favoured races in the struggle for life / by Charles Darwin. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

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    of body or constitution, causing coughs or colds, rheumatism, or inflammations of various organs. With respect to what I have called the indirect action of changed conditions, namely, through the reproductive system being affected, we may infer that variability is thus induced, partly from the fact of this system being extremely sensitive to any change in the con- ditions, and partly from the similarity, as Kolreuter and others have remarked, between the variability which follows from the crossing of distinct species, and that which may he observed with plants and animals when reared under new or unnatural conditions. Many facts clearly show how eminently susceptible the reproduc- tive system is to very slight changes in the surrounding conditions. Nothing is more easy than to tame an animal, and few things more difficult than to get it to breed freely under confinement, even when the male and female unite. How many animals there are which will not breed, though kept in an almost free state in their native country ! This is generally, but erroneously, attributed to vitiated instincts. Many cultivated plants display the utmost vigour, and yet rarely or never seed! In some few cases it has been discovered that a very trifling change, such as a little more or less water at some particular period of growth, will determine whether or not a plant will produce seeds. I cannot here give the details which I have collected and elsewhere published on this curious subject; but to show how singular the laws are which determine the repro- duction of animals under confinement, I may mention that car- nivorous animals, even from the tropics, breed in this country pretty freely under confinement, with the exception of the planti- grades or bear family, which seldom produce young; whereas carnivorous birds, with the rarest exceptions, hardly ever lay fertile eggs. Many exotic plants have pollen utterly worthless, in the same condition as in the most sterile hybrids. When, on the one hand, we see domesticated animals and plants, though often weak and sickly, breeding freely under confinement; and when, on the other hand, we see individuals, though taken young from a state of nature perfectly tamed, long-lived and healthy (of which I could give numerous instances), yet having their reproductive system so seriously affected by unperceived causes as to fail to act, we need not be surprised at this system, when it does act imder confinement, acting irregularly, and producing offspring somewhat unlike their parents. I may add, that as some organisms breed freely under the most unnatural conditions (for instance, rabbits and ferrets kept in hutches), showing that their reproductive organs are not easily affected; so will some animals and plants withstand domestication