| → and then to 1872 |
| and to 1859 1860 1861 1866 |
| or 1869 |
|
| → may, in many cases, be the simple result of 1872 |
| and higher stage may be, in some cases, due merely to 1859 1860 1866 |
| and higher stage may be; in some cases, due merely to 1861 |
| may, in some cases, be the simple result of 1869 |
|
| ↑ 1 blocks not present in 1872; present in 1859 1860 1861 1866 1869 |
| the long-continued action of different physical conditions
in two different regions; but I have not much faith in this view; and I attribute the passage of a variety, from a state in which it differs very slightly from its parent to one in which it differs more,
to the action
of natural selection
in accumulating (as will hereafter
be more fully explained)
differences of structure in certain definite directions.
|
|
| → A 1872 |
| Hence I believe a 1859 1860 1861 1866 |
| Hence a 1869 |
|
| → considerations to be 1872 |
| views 1859 1860 1861 1866 |
| considerations 1869 |
|
| → OMIT 1869 1872 |
| whilst in this incipient state 1859 1860 1861 1866 |
|
| → Madeira, and with plants by Gaston de Saporta. 1869 1872 |
| Madeira. 1859 1860 1861 1866 |
|
| →
,
much diffused
,
1872 |
|
much-diffused,
1866 1869 |
|
|
more
and
permanent varieties; and at
latter, as leading to
→and then to
species. The
from one stage of difference to another
→may, in many cases, be the simple result of
↑
the nature of the organism and of the different physical conditions to which it has long been exposed; but with respect to the more important and adaptive characters, the passage from one stage of difference to another, may be safely attributed to the cumulative action of natural selection, hereafter to be explained, and to the effects of the increased use or disuse of parts.
→A
well-marked variety may
called an incipient species; but whether this belief
justifiable must be judged
by the
weight of the
facts and
→considerations to be
given throughout this work. |
|
| It need not be supposed that all varieties or incipient species
attain the rank of species. They may
→OMIT
become extinct, or they may endure as varieties for very long periods, as has been shown to be the case by Mr. Wollaston with the varieties of certain fossil land-shells in
→Madeira, and with plants by Gaston de Saporta. If a variety were to flourish so as to exceed in numbers the parent species, it would
rank as the species, and the species as the variety; or it might come to supplant and exterminate the parent species; or both might co-exist, and both rank as independent species. But we shall hereafter
to
this subject. |
|
| From these remarks it will be seen that I look at the term
as one arbitrarily
for the sake of
to a set of individuals closely resembling each other, and that it does not essentially differ from the term variety, which is given to less distinct and more fluctuating forms. The term variety, again, in comparison with mere individual differences, is also applied arbitrarily,
for
sake. |
|
→
,
much diffused
,
and
common
Species
vary
most.
|
| Guided by theoretical considerations, I thought that some interesting results might be obtained in regard to the nature and relations of the species which vary most, by tabulating all the varieties in several well-worked floras. At first this seemed a simple task; but Mr. H. C.
to whom I am much indebted for valuable advice and assistance on this subject, soon convinced me that there were many difficulties, as did subsequently Dr. Hooker, even in stronger terms. I shall reserve for
future work the discussion of these difficulties, and the tables
of the proportional numbers of the varying species. Dr. Hooker permits me to add, that after having carefully read my manuscript, and examined the
|
