Focusing on artificial insemination by donor (AID), the article examines the social logic which underlies the principle of anonymity of the semen donor. The central argument is that the strategy of disguising his identity, and other similar social devices, evince a two-folded aspect: on one hand, they convey an uneasiness anchored on the identification between family ties and biology/nature. From this point of view, the social mechanisms analyzed point to a priority conferred to bjological constraints over the social ones. But on the other hand, and at the same time, the strategy of anonymity and other similar ones can be deemed as social devices meant to bypass the strength, supposedly irresistible, of natural ties. From this point of view, human will and/or culture are conceived as capable of manipulating and subordinating natural forces. Based on this inherent duplicity of the social devices analyzed, the article suggests that they are expressive of a wider dilemma: the one of the tension in the way of conceiving the relative strength between nature over culture or culture over nature.