- When two people have a relationship they unify their souls.
- When the relationship is prohibited, residue of impurity is left in the women's body.
-This residue will effect the children coming from this lady even if they are from another man.
- This is why Kayin was the way he was, since he carried the bulk of the zuhama left in Chavah form the Nachash Hadmony.(primeval serpent)
- Another example is Shul ben Hknanis who was the son of Denah from Shimon but was greatly affected by the impurity left over from Shichem.
- Normally it clears out after one or two children.
- This also explains many contradictory Midrahsim regarding peoples fathers, example by Og and Sichon.