The scripture writer gives two main reasons behind this the seed and the place. Various commentator explain it thus - 'seed' is the term used for male semen and female menstrual secretion. Generally, birth of man, woman and eunuch takes place owing to different seeds. If man's semen and woman's menstrual secretion both posses the potential for childhood, are flowless and the quantity of semen is more than the quantity of female secretion, a male child is born, if female secretion overweighs the male semen, a girl child is born and if both are in exactly same quantity, an eunuch is born.
A healthy state of a woman below 55 and a man below 70 is the last age limit for child production. Apart from this, semen and female secretions too are fit for child production only for about 12 muhurta; then their power is lost and they die. The other reason for differentiation is the placing of the embryo in mother's womb decides the child's sex. Generally, a embryo placed in the right side of the womb gives birth to a male child; from the left side female child is born while if the both sides are involved, an eunuch is born.
Apart from this factor, most important of all, responsible for maleness, femaleness and eunuchness is the karmas of creature. This is not the theory that a woman in the next birth shall be born only a woman or a man shall be born only a man. All this depend upon their karmas. Combination of "seed and place" takes place according to soul's karmas.[62]