Ukrainian origins of R1a1, and a postglacial spread of the R1a1 gene during the Late Glacial, subsequently magnified by the expansion of the Kurgan culture into Europe and eastward. Spencer Wells proposes central Asian origins, suggesting that the distribution and age of R1a1 points to an ancient migration corresponding to the spread by the Kurgan people in their expansion from the Eurasian Steppe. According to Pamjav et al. (2012), "Inner and Central Asia is an overlap zone for the R1a1-Z280 and R1a1-Z93 lineages [which] implies that an early differentiation zone of R1a1-M198 conceivably occurred somewhere within the Eurasian Steppes or the Middle East and Caucasus region as they lie between South Asia and Eastern Europe." A 2014 study by Peter A. Underhill et al., using 16,244 individuals from over 126 populations from across Eurasia, concluded that there was compelling evidence that "the initial episodes of haplogroup R1a diversification likely occurred in the vicinity of present-day Iran." According to Martin P. Richards, co-author of , "[the prevalence of R1a in India was] very powerful evidence for a substantial Bronze Age migration from central Asia that most likely brought Indo-European speakers to India." Literary research: similarities, geography, and references to migration Similarities Mitanni The oldest inscriptions in Old Indic, the language of the Rig Veda, is found not in India, but in northern Syria in Hittite records regarding one of their neighbors, the Hurrian-speaking Mitanni. In a treaty with the Hittites, the king of Mitanni, after swearing by a series of Hurrian gods, swears by the gods Mitrašil, Uruvanaššil, Indara, and Našatianna, who correspond to the Vedic gods Mitra, Varuna, Indra, and Nāsatya (Aśvin). Contemporary equestrian terminology, as recorded in a horse-training manual whose author is identified as "Kikkuli", contains Indo-Aryan loanwords. The personal names and gods of the Mitanni aristocracy also bear significant traces of Indo-Aryan. Because of the association of Indo-Aryan with horsemanship and the Mitanni aristocracy, it is presumed that, after superimposing themselves as rulers on a native Hurrian-speaking population about the 15th–16th centuries BCE, Indo-Aryan charioteers were absorbed into the local population and adopted the Hurrian language. Brentjes argues that there is not a single cultural element of central Asian, Eastern European, or Caucasian origin in the Mitannian area; he also associates with an Indo-Aryan presence the peacock motif found in the Middle East from before 1600 BCE and quite likely from before 2100 BCE. Scholars reject the