Central Asia is a region where multiple ethnic and racial groups have mixed over the course of history, and the main reason for that is that it was the main route between Asia and Europe, where mostly nomadic people lived in.
In general, the population in Central Asia is a mixture of Iranian people, Mongol People, Turkic people, Caucasus people, and Slavic people. Depending on how much mixture and which ethnic or racial group was more dominating in a region, physical appearances started to develop unique for each part of the region.
The Kazakhs and Kyrgyz people are more Mongol like, and that is because of the bigger Mongol genetic influence, the people in Turkmenistan and Uzbekistan vary from typical Turkic, to Caucasoid, and that is because the pretty even genetic contribution of Iranian, Turkic, and Caucasoid people. The Tajiks look pretty much the same as the Iranians, which is because of their Iranian origin, and on top of that, there's places dominated by totally Caucasoid people which are of Russian origin, mostly in Kazakhstan.
