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Prolonged interbreeding in any species can eventually lead to serious birth defects. Harmful genetic mutations are less likely to appear in large populations where individuals reproduce with random partners due to the wider variety of genetic mutations.
长期来看，任何物种间的异血缘繁殖终会导致严重的先天缺陷。人口多的地方，个体间随机繁衍，恶性基因突变的几率降低很多，因为基因突变的种类更广泛。
But in small, isolated populations where inbreeding is common, there’s a greater chance that related partners carry the same mutations.
反之，在人口小且封闭的地方，近亲交配的现象十分普遍，有血缘的伴侣携带相同基因突变的几率更大。
However, harmful effects are more common in groups with a history of interbreeding over several generations.
然而，恶性先天缺陷常见于家族多代异血缘交配。
First cousins that are not from such groups run only a slightly greater risk of producing children with birth defects than non-related couples.
表亲生育的孩子患先天缺陷的风险略高于无血缘伴侣生育的孩子。
Although such risks should not be ignored, first cousin marriage is not necessarily a recipe for genetic disaster.
虽然这样的风险不容忽视，但是表亲结婚并非注定会引发基因灾难。
译文来自可可英语
