| → species belonging to the same genus. 1872 |
| species. 1869 |
|
| ↑ 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.
|
|
| → by acting directly 1872 |
| directly by acting 1869 |
|
| → of which correlated growth is probably the most important. 1872 |
| more especially by that of correlation of growth. 1859 1860 1861 1866 |
| more especially by that of correlation. 1869 |
|
| → but how much we do not know, may 1872 |
| may 1859 1860 1861 1866 1869 |
|
| → life. 1859 1860 1861 1866 1872 |
| life, but how much we do not know. 1869 |
|
| → Some, perhaps a great, effect may 1872 |
| Something must 1859 1860 1861 1866 1869 |
|
| → the increased use or disuse of parts. 1872 |
| use and disuse. 1859 1860 1861 1866 1869 |
|
|
but the goose, under the conditions to which it is exposed when domesticated, seems to have a singularly inflexible organisation, though it has varied to a slight extent, as I have elsewhere described. |
|
| Some authors have maintained that the amount of variation in our domestic productions is soon reached, and can never afterwards be exceeded. It would be somewhat rash to assert that the limit has been attained in any one case; for almost all our animals and plants have been greatly improved in many ways within a recent period; and this implies variation. It would 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 belonging to the same genus. 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
→by acting directly
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,
→of which correlated growth is probably the most important.
→but how much we do not know, may
be attributed to the
action of the conditions of
→life.
→Some, perhaps a great, effect may
be attributed to
→the increased use or disuse of parts.
|
