general reliability of Vedic texts, discounting the like of: Ecological studies: widespread drought, urban collapse, and pastoral migrations 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. Steppe herders, archaic Proto-Indo-European speakers, spread into the lower Danube valley about 4200–4000 BCE, either causing or taking advantage of the collapse of Old Europe. The Yamna horizon was an adaptation to a climate change which occurred between 3500 and 3000 BCE, in which the steppes became drier and cooler. Herds needed to be moved frequently to feed them sufficiently, and the use of wagons and horse-back riding made this possible, leading to "a new, more mobile form of pastoralism". In the third millennium BCE widespread aridification led to water shortages and ecological changes in both the Eurasian steppes and the Indian subcontinent. On the steppes, humidification led to a change of vegetation, triggering "higher mobility and transition to nomadic cattle breeding". Water shortage also had a strong impact in the Indian subcontinent, "causing the collapse of sedentary urban cultures in south central Asia, Afghanistan, Iran, and India, and triggering large-scale migrations". Development of the theory Similarities between Sanskrit, Persian, Greek In the 16th century, European visitors to India became aware of similarities between Indian and European languages and as early as 1653 Van Boxhorn had published a proposal for a proto-language ("Scythian") for Germanic, Romance, Greek, Baltic, Slavic, Celtic and Iranian. In a memoir sent to the French Academy of Sciences in 1767 Gaston-Laurent Coeurdoux, a French Jesuit who spent all his life in India, had specifically demonstrated the existing analogy between Sanskrit and European languages. In 1786 William Jones, a judge in the Supreme Court of Judicature at Fort William, Calcutta, linguist, and classics scholar, on studying Sanskrit, postulated, in his Third Anniversary Discourse to the Asiatic Society, a proto-language uniting Sanskrit, Persian, Greek, Latin, Gothic and Celtic languages, but in many ways his work was less accurate than his predecessors', as he erroneously included Egyptian, Japanese and Chinese in the Indo-European languages, while omitting Hindustani and Slavic: Jones concluded that all these languages originated from the same source. Homeland Scholars assume a homeland either in central Asia or in Western Asia, and Sanskrit must in this case have