	According to Laurie Patton, a professor of Religion specialising on early Indian religions, the rights and status of Shudra varies widely across early Indian texts. While section 9.15 of "Atharvaveda" states Shudras may undertake thread wearing ceremony ("upanayana"), the "Apastamba Grhysutra" states they may not and excludes the Shudra students from hearing or learning the Vedas. "Yajnavalkya Smriti" in contrast mentions Shudra students, and the "Mahabharata" states that all four varnas including the Shudras may hear the Vedas. Other Hindu texts go further and state that the three varnas – Brahmin, Kshatriya, Vaishya – may acquire knowledge from Shudra teachers, and the "yajna" sacrifices may be performed by Shudras. These rights and social mobility for Shudras may have arisen in times of lower societal stress and greater economic prosperity, periods that also saw the improvement in the social conditions of women.