In the Altai region specifically, the climate was cooler and drier than modern conditions, with the ecological zones shifted toward a steppe-dominated landscape rich in large herbivores.

In cold periods, the ranges of human populations contracted toward more habitable zones — river valleys, sheltered mountain territories, areas with reliable food resources.

This contraction could have pushed Neanderthal and Denisovan populations into closer proximity in the areas that remained hospitable, increasing the frequency of encounters between them.

Climate fluctuations during the Pleistocene were dramatic and frequent.

Periods of relative warmth alternated with periods of intense cold, and each transition caused major reorganization of ecological communities and the human populations that depended on them.

Population ranges expanded during warm periods and contracted during cold periods.