在人类刚刚从动物脱胎出来的时期,两性生活杂乱无章,没有辈份、亲缘的分别,优势原则起决定性作用。这种状况,一方面使同性之间经常发生争夺异性的冲突,有的人甚至丧命于这种争夺和冲突中。另一方面,这种杂乱性关系造成了一部分人由于近亲血统而在自然选择中淘汰。这样,原始人就自觉或不自觉地意识到了在某些条件下性生活对人类生存的危险性,便开始对性关系加以规范、限制,于是性的禁忌就产生了。人类最先的性禁忌,根据摩尔根 At a time when human beings have just been born from animals, the sex life is disorganized, without distinction of generation and affinity, and the principle of advantage plays a decisive role. This situation, on the one hand, leads to clashes often clash between heterosexuals of the same sex, and some people even die in such contention and conflict. On the other hand, this messy relationship caused some people to be eliminated in natural selection because of their kinship. In this way, the primitive people consciously or unconsciously aware of under certain conditions, the danger of sexual life to human survival, they began to regulate sexual relations, restrictions, so the taboo of sex was born. The first human sexual taboo, according to Morgan