| → form it into 1872 |
| have formed 1859 1860 1861 1866 1869 |
|
| → or more 1872 |
| generations; but it would have been better if each had represented ten thousand 1859 1860 1861 1866 |
| generations, or ten thousand. 1869 |
|
| → commonly 1872 |
| generally to vary 1859 1860 1861 1866 1869 |
|
| → did their parents. 1872 |
| their parents varied. 1859 1860 1861 1866 1869 |
|
| → all these circumstances are 1872 |
| these circumstances we know to be 1859 1860 1861 1866 1869 |
|
| →
a
2
,
1859 1861 1866 1869 1872 |
|
a
2
,
1860 |
|
| →
a
1
.
1859 1861 1866 1869 1872 |
|
a
1
.
1860 |
|
| →
s
2
,
1859 1861 1869 1872 |
|
s
2
,
1860 |
|
8
2
,
1866 |
|
| → irregular, nor that it goes on continuously; it is far more probable that each form remains for long periods unaltered, and then again undergoes modification. 1866 1869 1872 |
| irregular. 1859 1860 1861 |
|
|
by the outer dotted lines) being preserved and accumulated by natural selection. When a dotted line reaches one of the horizontal lines, and is there marked by a small numbered letter, a sufficient amount of variation is supposed to have been accumulated to
→form it into
a fairly well-marked variety, such as would be thought worthy of record in a systematic work. |
|
| The intervals between the horizontal lines in the diagram, may represent each a thousand
→or more
After a thousand generations, species (A) is supposed to have produced two fairly well-marked varieties, namely
and
m
1
.
These two varieties will generally
be exposed to the same conditions which made their parents variable, and the tendency to variability is in itself
consequently they will
to vary, and
→commonly
in nearly the same manner as
→did their parents. Moreover, these two varieties, being only slightly modified forms, will tend to inherit those advantages which made their
parent (A) more numerous than most of the other inhabitants of the same country; they will
partake of those more general advantages which made the genus to which the parent-species belonged, a large genus in its own country. And
→all these circumstances are
to the production of new varieties. |
|
| If, then, these two varieties be variable, the most divergent of their variations will generally be preserved during the next thousand generations. And after this interval, variety
a
1
is supposed in the diagram to have produced variety
→
a
2
,
which will, owing to the principle of divergence, differ more from (A) than did variety
→
a
1
.
Variety
m
1
is supposed to have produced two varieties, namely
m
2
and
→
s
2
,
differing from each other, and more considerably from their common parent (A). We may continue the process by similar steps for any length of time; some of the varieties, after each thousand generations, producing only a single variety, but in a more and more modified condition, some producing two or three varieties, and some failing to produce any. Thus the varieties or modified
the common parent (A), will generally go on increasing in number and diverging in character. In the diagram the process is represented up to the ten-thousandth generation, and under a condensed and simplified form up to the fourteen-thousandth generation. |
|
| But I must here remark that I do not suppose that the process ever goes on so regularly as is represented
the diagram, though in itself made somewhat
→irregular, nor that it goes on continuously; it is far more probable that each form remains for long periods unaltered, and then again undergoes modification. Nor do I suppose
|
