在此之前的 20 年，我们总是在讨论，人与动物的嵌合体是否允许活下来；但我们很少论及，当嵌合体还只是一个早期胚胎（例如囊胚）时应该怎么处理。囊胚里含有人细胞，这问题比把人细胞移植到动物体内要复杂得多——如果只是定向移植，研究者可以预测人细胞在动物体内的发育，避免它们出现在一些在伦理上敏感的区域，例如能够产生意识的大脑、可能产生后代的生殖系统等。但是，囊胚
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