Mainly on three factors : the rapid increase in literacy particularly among women a falling birthrate and a significant decline in the widespread custom of endogamy or marriage between first cousins .
From this primitive indifference they may have advanced , some to endogamy , some to exogamy .
从这种原始的漠不关心中,它们可能取得了发展,有的走向内婚制,有的走向外婚制。
It may be noted , however , that endogamy appears in populations formed by the fusion of many tribes , as the almost uniform characteristic of the dominant race .
Hereafter we shall see how a tribe organized on the principle of endogamy might be developed from one organized on the principle of exogamy , in perfect consistency with the law against the intermarriage of relations .