On 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:
1859
Catalogue details

Licence: Public Domain Mark

Credit: On 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.

    16/546 (page 8)
    8 VARIATION Chap. I. No case is on record of a variable being ceasing to be variable under cultivation. Our oldest cultivated plants, such as wheat, still often yield new varieties : our oldest domesticated animals are still capable of rapid improve¬ ment or modification. It has been disputed at what period of life the causes of variability, whatever they may be, generally act ; whether during the early or late period of development of the embryo, or at the instant of conception. Geoffroy St. Hilaire's experiments show that unnatural treatment of the embryo causes monstrosities ; and monstrosities cannot be separated by any clear line of distinction from mere variations. But I am strongly inclined to suspect 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 con¬ ception. Several reasons make me believe in this ; but the chief one is the remarkable effect which confine¬ ment or cultivation has on the functions of the repro¬ ductive system ; this system appearing to be far more susceptible than any other part of the organisation, to the action of any change in the conditions of life. No¬ thing is more easy than to tame an animal, and few things more difficult than to get it to breed freely under confinement, even in the many cases when the male and female unite. How many animals there are which will not breed, though living long under not very close con¬ finement in their native country! This is generally attributed to vitiated instincts ; but how many cultivated plants display the utmost vigour, and yet rarely or never seed ! In some few such cases it has been found out that very trifling changes, such as a little more or less water at some particular period of growth, will determine whether or not the plant sets a seed. I cannot here enter on the copious details which I have collected on