Results of studies based upon autosomal DNA variation have also been varied. In a major study (2009) using over 500,000 biallelic autosomal markers, Reich hypothesized that the modern South Asian population was the result of admixture between two genetically divergent ancestral populations dating from the post-Holocene era. These two "reconstructed" ancient populations he termed "Ancestral South Indians" (ASI) and "Ancestral North Indians" (ANI). According to Reich: "ANI ancestry is significantly higher in Indo-European than Dravidian speakers, suggesting that the ancestral ASI may have spoken a Dravidian language before mixing with the ANI." While the ANI is genetically close to Middle Easterners, Central Asians and Europeans, the ASI is not closely related to groups outside of the subcontinent. As no "ASI" ancient DNA is available, the indigenous Andamanese Onge are used as an (imperfect) proxy of ASI (according to Reich et al., the Andamanese, though distinct from them, are the closest living population to ASI). According to Reich et al., both ANI and ASI ancestry are found all over the subcontinent (in both northern and southern India) in varying proportions, and that "ANI ancestry ranges from 39-71% in India, and is higher in traditionally upper caste and Indo-European speakers."