Srauta Sutra of Baudhayana According to Romila Thapar, the Srauta Sutra of Baudhayana "refers to the Parasus and the arattas who stayed behind and others who moved eastwards to the middle Ganges valley and the places equivalent such as the Kasi, the Videhas and the Kuru Pancalas, and so on. In fact, when one looks for them, there are evidence for migration." Later Vedic and Hindu texts Texts like the Puranas and Mahabharata belong to a much later period than the Rigveda, making their evidence less than sufficient to be used for or against the Indo-Aryan migration theory. Later Vedic texts show a shift of location from the Punjab to the East. According to the Yajurveda, Yajnavalkya (a Vedic ritualist and philosopher) lived in the eastern region of Mithila. Aitareya Brahmana 33.6.1. records that Vishvamitra's sons migrated to the north, and in Shatapatha Brahmana 1:2:4:10 the Asuras were driven to the north. In much later texts, Manu was said to be a king from Dravida. In the legend of the flood he stranded with his ship in Northwestern India or the Himalayas. The Vedic lands (e.g. Aryavarta, Brahmavarta) are located in Northern India or at the Sarasvati and Drishadvati river. However, in a post-Vedic text the Mahabharata Udyoga Parva (108), the East is described as the homeland of the Vedic culture, where "the divine Creator of the universe first sang the Vedas". The legends of Ikshvaku, Sumati and other Hindu legends may have their origin in Southeast Asia. The Puranas record that Yayati left Prayag (confluence of the Ganges & Yamuna) and conquered the region of Sapta Sindhu. His five sons Yadu, Druhyus, Puru, Anu and Turvashu correspond to the main tribes of the Rigveda. The Puranas also record that the Druhyus were driven out of the land of the seven rivers by Mandhatr and that their next king Gandhara settled in a north-western region which became known as Gandhara. The sons of the later Druhyu king Prachetas are supposed by some to have 'migrated' to the region north of Afghanistan though the Puranic texts only speak of an "adjacent" settlement. Ecology Climate change and drought may have triggered both the initial dispersal of Indo-European speakers, and the migration of Indo-Europeans from the steppes in south-central Asia and India. Around 4200–4100 BCE a climate change occurred, manifesting in colder winters in Europe. Between 4200 and 3900 BCE many tell settlements