Such a process may set in automatically among those people where a strong racial instinct has remained. Among such people we may count those elements which, for some particular cause such as coercion, have been thrown out of the normal way of reproduction along strict racial lines. As soon as this compulsion ceases, that part of the race which has remained intact will tend to marry with its own kind and thus impede further intermingling. Then the mongrels recede quite naturally into the background unless their numbers had increased so much as to be able to withstand all serious resistance from those elements which had preserved the purity of their race.