 The Altai Mountains experienced a period of warmer and wetter conditions between 6.5 and 3.6 thousand years ago, known as the Altai Holocene Climatic Optimum, AHCO. This climatic optimum was conducive to the expansion of prehistoric human populations and increased cultural exchange across the Central Asian steppe. This article was authored by Li Xiong Xiong, Xiaozong Huang, Mingjie Sun, and others.