| →
(
a
14
1869 |
|
(
a
14
1872 |
|
| →
m
14
),
1869 |
|
m
14
),
1872 |
|
| → half a dozen 1869 |
| half-a-dozen 1872 |
|
| ↑ 1 blocks not present in 1866 1869 1872; present in 1859 1860 1861 |
| These two families, however, would be less distinct from each other than they were before the discovery of the fossils.
|
|
| → some slight 1859 1860 1861 1866 1869 |
| a greater or less 1872 |
|
| → are 1869 1872 |
| seem to me 1859 1860 1861 1866 |
|
|
So
if the three families formed of eight genera
→
(
a
14
to
→
m
14
),
on the uppermost line, be supposed to differ from each other by
→half a dozen
important characters, then the families which existed at the period marked VI. would certainly have differed from each other by a less number of characters; for they would at this early stage of descent have diverged in a less degree from their common progenitor. ↑ Thus it comes that ancient and extinct genera are often in
→some slight
degree intermediate in
between their modified descendants, or between their collateral relations. |
|
|
nature the
will be far more complicated than is represented in the diagram; for the groups will have been more
they will have endured for extremely unequal lengths of time, and will have been modified in various degrees. As we possess only the last volume of the geological record, and that in a very broken condition, we have no right to expect, except in
rare cases, to fill up
intervals in the natural system, and thus
distinct families or orders. All that we have a right to
that those
which
within known geological
undergone much modification, should in the older formations make some slight approach to each other; so that the older members should differ less from each other in some of their characters than do the existing members of the same groups; and this by the concurrent evidence of our best palæontologists
frequently
the case. |
|
| Thus, on the theory of descent with modification, the main facts with respect to the mutual affinities of the extinct forms of life to each other and to living forms,
→are
explained in a satisfactory manner. And they are wholly inexplicable on any other view. |
|
| On this same theory, it is evident that the fauna
|
