In the current cycle of creation, tamo yuga, prANi yuga and Adi yuga were followed by a period named maNijA where human society reached a new level of evolution. Skills such as agriculture, irrigation etc were mastered and the society was classified into four divisions: sAdhya, mahArAjika, AbhAsvara and tuShita. This was the early origin of the chAturvarNya system in the upcoming deva yuga. The sAdhyas were men of scientific and spiritual thinking, somewhat similar to the brAhmaNas of deva yuga. mahArAjikas were rulers and warriors, AbhAsuras [AbhAsvaras] were merchants and skilled workers and tuShitas served the other three classes. The sAdhyas were masters of yajna vidyA, which was later propagated during deva yuga by sage atharvA, son of brahmA, among the deva-trilokI. The sAdhyas however were nirIshwaravAdins which is indicated by words such as pUrve devAH, suradviShaH etc. The sAdhyas did not accept an omnipresent and omniscient Ishvara but instead relied on kShaNika vij~nAna, perceivable through the sensory faculties. They ascribed the universe and its function to the rules of nature and refused to believe in the existence of a Supreme Power. Due to the utkarSha of these thinkers, the maNijA yuga came to be known as sAdhya yuga. sadvAda, asadvAda, sadasadvAda, vyomavAda, aparavAda, rajovAda, ambhovAda, AvaraNavAda, ahorAtravAda and samshayavAda were ten siddhAntas [recorded in Rg Veda] prevalent in maNijA yuga. A great being named brahmA arose in thus yuga by the grace of parAshakti and disproved these dasha vAdas to establish brahmavAda on a firm foundation, propounding the concept of Ishvara sattA. The same brahmA came to be the pravartaka of the glorious deva yuga.
After establishing ekeshvaravAda, brahmA classified the earth into devatrilokI and asuratrilokI. himAlayan and Pamir regions came to be called as svarga ruled by indra and the residents came to be called devas. Regions of Africa and present America came to be called asura trilokI. The Devas lived in the region spreading across the Himalayan range till the sharyaNAvata. The residents of deva trilokI were classified as: R^iShi, pitr, devatA, devayoni and manuShya. The original R^iShis were prANa tattvas and those who realized these tattvas came to be called by the same name. From mUla prANa or R^iShi prANa, pitr prANa or saumya prANa originated. The pitr loka was inhabited by those with well-developed pitr prANa and were ruled by vaivasvata yama, son of svAyambhuva vivasvAn. The saumya prANa underwent a two-fold division based on sneha and teja resulting in the tattvas bhR^igu and a~NgirA. This yuga, where a deva vyavasthA existed on the earth, came to be called as deva yuga. Without an understanding of deva yuga, the significance or the concept of shakti yuga can never be understood.