And all these circumstances are favourable 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 a1 is supposed in the diagram to have produced variety a2, which will, owing to the principle of divergence, differ more from (A) than did variety a1.

Variety m1 is supposed to have produced two varieties, namely m2 and s2, 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 descendants of the common parent (A), will generally go on increasing in number and diverging in character.