The Lord is giving a genealogical synopsis of the universal population. Brahma is the original creature born out of the energy of the Supreme Lord, who is known as Hiranyagarbha. And from Brahma all the seven great sages, and before them four other great sages, named Sanaka, Sananda, Sanatana and Sanat-kumara, and the Manus, are manifested. All these twenty-five great sages are known as the patriarchs of the living entities all over the universe. There are innumerable universes and innumerable planets within each universe, and each planet is full of population of different varieties. All of them are born of these twenty-five patriarchs. Brahma underwent penance for one thousand years of the demigods before he realized by the grace of Krishna how to create. Then from Brahma came Sanaka, Sananda, Sanatana and Sanat-kumara, then Rudra, and then the seven sages, and in this way all the brahmanas and kshatriyas are born out of the energy of the Supreme Personality of Godhead. Brahma is known as Pitamaha, the grandfather, and Krishna is known as Prapitamaha, the father of the grandfather. That is stated in the Eleventh Chapter of the Bhagavad-gita (11.39).