| → species. 1869 |
| species belonging to the same genus. 1872 |
|
| ↑ 1 blocks not present in 1869 1872; present in 1859 1860 1861 1866 |
| I believe that the conditions of life, from their action on the reproductive system, are so far of the
highest importance as causing variability.
|
|
| → directly by acting 1869 |
| by acting directly 1872 |
|
| → more especially by that of correlation. 1869 |
| more especially by that of correlation of growth. 1859 1860 1861 1866 |
| of which correlated growth is probably the most important. 1872 |
|
|
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
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
Eclipse was far fleeter, and a dray-horse is incomparably stronger than any two
→species. So with plants, the seeds of the different varieties of the bean or maize
more in size, than do the seeds of the distinct species in any one genus
the same two families. The same remark holds good in regard to the fruit of the several varieties of the plum, and still more
with the melon, as well as in
other analogous cases. |
|
| To sum up on the origin of our
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.
|
