| → I believe that during the slow process of modification 1859 1860 1861 1866 |
| OMIT 1869 1872 |
|
| → species will have been 1859 1860 1861 1866 |
| same species inhabiting the same area will be 1869 1872 |
|
| → will not have been due, 1859 1860 1861 1866 |
| OMIT 1869 1872 |
|
| → to 1859 1860 1861 1866 |
| will not be due to 1869 1872 |
|
| → facts. 1859 1860 1861 1866 1869 |
| facts. Change of climate must have had a powerful influence on migration. 1872 |
|
| → Change of climate must have had a powerful influence on migration: a region when 1859 1860 1861 1866 |
| Change of climate must have had a powerful influence on migration; an impassable region when 1869 |
| A region now impassable to certain organisms from the nature of 1872 |
|
| → was different may 1859 1860 1861 1866 |
| was different from what it now is, may 1869 |
| might 1872 |
|
| → but now be impassable; 1859 1860 1861 1866 |
| when the climate was different. 1872 |
| OMIT 1869 |
|
|
a single parent. But in the
of cases, namely, with all organisms which habitually unite for each birth, or which
intercross,
→I believe that during the slow process of modification
the individuals of the
→species will have been
kept nearly uniform by intercrossing; so that many individuals will
on simultaneously changing, and the whole amount of modification
→will not have been due,
at each
→to
descent from a single parent. To illustrate what I mean: our English
differ
from the horses of every other breed; but they do not
their
and
to descent from any single pair, but to continued care in
and training
individuals during
|
|
| Before discussing the three classes of facts, which I have selected as presenting the greatest amount of difficulty on the theory of
centres of
I must say a few words on the means of dispersal. |
|
|
| Sir C. Lyell and other authors have ably treated this subject. I can give here only the briefest abstract of the more important
→facts.
→Change of climate must have had a powerful influence on migration: a region when
its
→was different may
have been a high road for
→but now be impassable;
I shall, however, presently have to discuss this branch of the subject in some detail. Changes of level in the land must also have been highly influential: a narrow isthmus now separates two marine faunas; submerge it, or let it formerly have been submerged, and the two faunas will now blend
may formerly have
the sea now extends, land may at
former
have connected islands or possibly even continents together, and thus have allowed terrestrial productions to pass from one to the other.
|
