| → If, for instance, we suppose the existing genera of the two families 1859 1860 1861 |
|
So again, if the three families formed of eight genera (
a
14,
to
m
14
), on the uppermost line, be supposed
1866 |
|
| → a dozen characters, in this case the genera, 1859 1860 1861 |
| half a dozen important characters, then the families which existed 1866 |
|
| → differ 1859 1860 1861 |
| certainly have differed from each other 1866 |
|
| → at 1859 1860 1861 |
| they would at 1866 |
|
| → character from the 1859 1860 1861 |
| a less degree from their 1866 |
|
| → some slight 1859 1860 1861 1866 1869 |
| a greater or less 1872 |
|
| → seem to me 1859 1860 1861 1866 |
| are 1869 1872 |
|
|
discovery of the fossils.
→If, for instance, we suppose the existing genera of the two families
to differ from each other by
→a dozen characters, in this case the genera,
at the
period marked
would
→differ
by a
number of characters; for
→at
this early stage of descent
have
diverged in
→character from the
common
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,
→seem to me
explained in a satisfactory manner. And they are wholly inexplicable on any other view. |
|
| On this same theory, it is evident that the fauna
any
period in the earth's history will be
|
