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 , R1a1a diversified in the Eurasian Steppes or the Middle East and Caucasus region: Three genetic studies in 2015 gave support to the Kurgan theory of Gimbutas regarding the Indo-European Urheimat. According to those studies, haplogroups R1b and R1a, now the most common in Europe (R1a is also common in South Asia) would have expanded from the Pontic–Caspian steppes, along with the Indo-European languages; they also detected an autosomal component present in modern Europeans which was not present in Neolithic Europeans, which would have been introduced with paternal lineages R1b and R1a, as well as Indo-European languages. noted that R1a in South Asia most "likely spread from a single Central Asian source pool, there do seem to be at least three and probably more R1a founder clades within the Subcontinent, consistent with multiple waves of arrival." 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." Proposed South Asian origins Kivisild et al. (2003) have proposed either South or West Asia, while see support for both South and Central Asia. Sharma et al.(2009) showcased the existence of R1a in India beyond 18,000 years to possibly 44,000 years in origin. South Asian populations have the highest STR diversity within R1a1a, and subsequent older TMRCA datings, and R1a1a is present among both higher (Brahmin) castes and lower castes, although the frequency is higher among Brahmin castes. Nevertheless, the oldest TMRCA datings of the R1a haplogroup occur in the Saharia tribe, a scheduled caste of the Bundelkhand region. From these findings some researchers have concluded that R1a1a originated in South Asia, excluding a more recent, yet minor, genetic influx from Indo-European migrants in northwestern regions such as Afghanistan, Balochistan, Punjab, and Kashmir. However, this diversity, and the subsequent older TMRCA-datings, can also be explained by the historically high population numbers, which increases the likelihood of diversification and microsatellite variation. According to Sengupta et al. (2006), "[R1a1 and R2] could have actually arrived in southern India from a southwestern Asian source region multiple times." However, Sengupta also described in this article: This suggests that the origins of paternal haplogroup R1a