Does Prohibition Of Incest Needs Divine Guidance
Prohibition of relationship with Mother belongs to basic ethics/universal ethics but all other prohibitions arose with evolution of civilization and belong to the the domain of social ethics. In order to keep the sanctity of the instutution of marriage intact where no ulterior motive (i.e. sexual jealousy or sexual rivalry ) should come between different members of the same family, this prohibition was enforced after some time as relationships started to define themselves and the institution of family started taking its structural form in a society. In some instances, such societal ethics were extented further in sharia of Prophets e.g. In Islam, this prohibition extended to not having two sisters in Nikah at the same time or not having aunt and her niece in Nikah at the same time . As for the progeny of Prophet Adam (sws) and how their procreated, nothing can be said for sure, but even if it between siblings of alternate generations, then it is plausible and not objectionable in the light of the primitive societal ethics of that time. Following videos shed further light on this matter: Please refer to the video below from 16:40 to 20:19 https://youtu.be/o0hqdDwOrrI?t=1000
Please also refer to the video below from 1:37:20 to 1:44:09 and from 1:47:24 to 1:50:36 https://youtu.be/KhEG66tXw_8?t=5840