They would not be readily swamped by intercrossing or averaged off.
Other species of oak are intercrossing by the same process—the interchange of pollen at the time of blossoming.
But the lake-dwellers usually improved the breed by intercrossing with forms derived from their own fauna.
No one can deny that any degree and amount of intercrossing might take place in the case of icebergs.
Falsan and Chantre concerning the intercrossing, interosculation, and direct opposition of erratic paths in Savoy and Dauphiny.
It is only when intercrossing is checked, as when natural selection weeds out certain varieties, that evolution occurs.
On the other hand, intercrossing without producing an intermediate race is a test of dimorphism.
In this case, therefore, it is not intercrossing that has prevented the origin of local races.
These varieties would cross and blend where they met; but to this subject of intercrossing we shall soon have to return.
Evolution has to make head against the constant tendency of intercrossing to obliterate individual distinctions.