Origin of Species Variorum

Comparison with 1866

Text in this page (from paragraph 4550, sentence 300, word 3 to paragraph 4550, sentence 1000, word 32) is not present in 1866

To sum up on the origin of our Domestic Races of animals and plants. I believe that the conditions of life, from their action on the reproductive system, are so far of the highest importance as causing variability. ↑ I do not believe that variability is an inherent and necessary contingency, under all circumstances, with all organic beings, as some authors have thought. The effects of variability are modified by various degrees of inheritance and of reversion. Variability is governed by many unknown laws, more especially by that of correlation of growth. Something

be equally rash to assert that characters now increased to their utmost limit, could not, after remaining fixed for many centuries, again vary under new conditions of life. No doubt, as Mr. Wallace has remarked with much truth, a limit will be at last reached. For instance there must be a limit to the fleetness of any terrestrial animal, as this will be determined by the friction to be overcome, the weight of body to be carried, and the power of contraction in the muscular fibres. But what concerns us is that the domestic varieties of the same species differ from each other in almost every character, which man has attended to and selected, more than do the distinct species of the same genera. Isidore Geoffroy St. Hilaire has proved this in regard to size, and so it is with colour and probably with the length of hair. With respect to fleetness, which depends on many bodily characteristics, Eclipse was far fleeter, and a dray-horse is incomparably stronger than any two equine species. So with plants, the seeds of the different varieties of the bean or maize differ more in size, than do the seeds of the distinct species in any one genus of the same two families. The same remark holds good in regard to the fruit of the several varieties of the plum, and still more so with the melon, as well as in endless other analogous cases.

To sum up on the origin of our domestic races of animals and plants. ↑ Changed conditions of life are of the highest importance in causing variability, both directly by acting on the organisation, and indirectly by affecting the reproductive system. It is not probable that variability is an inherent and necessary contingent, under all circumstances. The greater or less force of inheritance and reversion determine whether variations shall endure. Variability is governed by many unknown laws, more especially by that of correlation. Some- thing