Nefesh HaChayim, Reb Itzele's Long Annotation

This is what they (OBM) stated (Sota 2a), that the assignment of a man’s first mate is not based on his actions, while the assignment of his second mate is based on his actions. As is known from the Zohar (Ehmore 104), during the act of intercourse of male and female, a tzellem awaits over them. This is the matter of the three aspects of the tzellem mentioned previously, for the combination of the four elements and the primeval roots are not equal in each of the NR”N. The outer garment is from the four elements. The brains are from the four roots, which are drawn upon according to the degree of holiness of the father and mother during the act of mating; at that moment it is not yet dependent upon the actions of the future fetus.