Grey wolves suffered a species-wide population bottleneck (reduction) approximately 25,000 YBP during the Last Glacial Maximum. This was followed by a single population of modern wolves expanding out of a Beringia refuge to repopulate the wolf's former range, replacing the remaining Late Pleistocene wolf populations across Eurasia and North America as they did so. This source population probably did not give rise to dogs, but it admixed with dogs which allowed them to gain coat colour genes that are also related to immunity. There is little genetic information available on the ancient wolves that existed prior to the bottleneck. However, studies show that one or more of these ancient populations is more directly ancestral to dogs than are modern wolves, and conceivably these were more prone to domestication by the first humans to expand into Eurasia.