The steppes of Central Asia are the perfect environment for animal husbandry, and archaeological remains of animals such as cattle and goats date back to 6,000 years ago. The domestication of the horse, dating back to the 3rd millennium B.C. in the area between the Dnieper and Volga Rivers (Anthony 1986; Cavalli-Sforza et al. 1994), may have been a particularly important event in the history of the people of the steppes, bringing changes, at all social levels, in subsistence, transportation, and warfare. On a general level, it allowed the development of a more pronounced pastoral nomadism, characterized by seasonal migrations over longer distances, much higher population mobility (Anthony [1986] proposes a factor of five), and, therefore, a higher likelihood of population growth and expansion. Archaeological records (Anthony 1986; Lin 1992; Dexter and Jones-Bley 1997) suggest that several expansion waves of nomadic groups from the Eurasian steppes reached Central Asia. They are described in Chinese historiography as horse-riding, Caucasian-looking, Indo-European speaking people and are sometimes referred as the "Kurgan Culture," with a homeland said to be in the steppes north of the Black and Caspian Seas (Dexter and Jones-Bley 1997).
Zerjal et al. (1999) postulated that haplogroup 3 could be the most evident male genetic legacy of this population expansion. It is interesting to note that haplogroup 3 is present at relatively low frequency in the Caucasus, as well as in the Middle East (Hammer et al. 2000; Semino et al. 2000). It is possible that, in the expansion of these early nomadic groups, the Caucasus mountain range formed a significant barrier and that the region was already well populated. Instead, they spread easily in eastern Central Asia, and haplogroup 3 is common in those populations, even though its distribution shows differing extremes of frequencythe Kyrgyz and the Tajiks show 63% and 64%, respectively, whereas the Kazaks show only 3%but these variations are probably the result of drift during population bottlenecks or founder events, as discussed below.
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