the idea that a race of people can be kept pure by not allowing people who are considered inferior (= of less value) to have children

One of the foundations of Hitler's social policies was the concept of racial hygiene. 种族优生的概念是希特勒的社会政策的基础之一。

An interest in questions of racial hygiene emerged, in various forms, round about 1890. 大约在1890年左右出现了关于种族优生的各种形式的问题。