| → have left behind them the 1869 1872 |
| the 1859 1860 1861 1866 |
|
| → are the descendants of 1866 1869 1872 |
| have descended from 1859 1860 1861 |
|
| → which constitute the 1872 |
| constituting the six 1859 1860 1861 |
| which constitute the several species of the 1866 1869 |
|
| → genera containing the several species; 1872 |
| genera. 1859 1860 1861 |
| genera; 1866 1869 |
|
| → each 1869 1872 |
| the 1859 1860 1861 |
| each of the 1866 |
|
| → genus having 1869 1872 |
| genera have all 1859 1860 1861 |
| genera having 1866 |
|
| → and this will 1872 |
| which would probably 1859 1860 1861 |
| and this probably would 1866 |
| and this probably will 1869 |
|
| → rich in fossil species of many kinds, and thick 1872 |
| thick 1859 1860 |
| rich in fossils and thick 1861 1866 |
| rich in fossil species of very many kinds and thick 1869 |
|
| → most of our 1861 1866 1869 1872 |
| the 1859 1860 |
|
|
in South
→have left behind them the
sloth, armadillo, and anteater, as their degenerate descendants. This cannot for an instant be admitted. These huge animals have become wholly extinct, and have left no progeny. But in the caves of Brazil, there are many extinct species which are closely allied in size and in
characters to the species still living in South America; and some of these fossils may
the actual progenitors of
species. It must not be forgotten that, on
theory, all the species of the same genus
→are the descendants of
some one species; so
if six genera, each having eight species, be found in one geological formation, and in
succeeding formation there be six other allied or representative genera
the same number of species, then we may conclude that
one species of each of the
older genera has left modified descendants,
→which constitute the
new
→genera containing the several species;
other seven species of
→each
old
→genus having
died out and
left no progeny. Or,
→and this will
be a far commoner case, two or three species
or three
of the six older genera will
the parents of the
new
the other
species and the other
having become utterly extinct. In failing orders, with the genera and species decreasing in
as
is the case
the Edentata of South America, still fewer genera and species will
modified blood-descendants. |
|
|
| I have attempted to show that the geological record is extremely imperfect; that only a small portion of the globe has been geologically explored with care; that only certain classes of organic beings have been largely preserved in a fossil state; that the number both of specimens and of species, preserved in our museums, is absolutely as nothing compared with the
number of generations which must have passed away even during a single formation; that, owing to subsidence being
for the accumulation of
deposits
→rich in fossil species of many kinds, and thick
enough to
future degradation,
intervals of time
elapsed between
→most of our
successive formations; that there has probably been more extinction during the periods of subsidence, and more variation during the periods of elevation, and during the latter the record will have been least perfectly kept; that each single formation has not been continuously deposited; that the duration of each formation is,
short compared with the average duration of specific forms; that migration has played an important part in the first appearance of new forms in any one area and formation; that widely ranging species are those which have varied
|
