Meanings of constant intermarriage in English

They are rapidly diminishing in numbers, chiefly no doubt on account of constant intermarriage.

They might all have been members of one family; indeed, this was practically the case, owing to constant intermarriage carried on for generations.

The children seemed very pale and anaemic, a condition which has been mainly brought about, I think, by the constant intermarriage among relations.

There was an extraordinary family resemblance in nearly all the heads one saw, which made one suspect constant intermarriage among relations in the small community.