Sometimes a sonless person offers his daughter to a husband on the condition that his grandson be returned to him to be adopted as his son and inherit his property. This is called putrika-dharma, which means that by execution of religious rituals one gets a son, although one is sonless by ones own wife. But here we see extraordinary behavior in Manu, for in spite of his having two sons, he handed over his first daughter to Prajapati Ruci on the condition that the son born of his daughter be returned to him as his son. Srila Visvanatha Cakravarti Thakura comments in this connection that King Manu knew that the Supreme Personality of Godhead would take birth in the womb of Akuti; therefore, in spite of having two sons, he wanted the particular son born of Akuti because he was ambitious to have the Supreme Personality of Godhead appear as his son and grandson. Manu is the lawgiver of mankind, and since he personally executed the putrika-dharma, we may accept that such a system may be adopted by mankind also. Thus, even though one has a son, if one wants to have a particular son from ones daughter, one may give ones daughter in charity on that condition. That is the opinion of Srila Jiva Gosvami.