Numbers of breeding woolly rhinos stayed relatively constant for tens of thousands of years until at least about 18,500 years ago, more than 13,000 years after people first reached northeastern Siberia, scientists report online August 13 in Current Biology. These findings build on a previous argument, based on dated fossils, that woolly rhino populations across northern Eurasia began to decline between 40,000 and 35,000 years ago, with surviving animals moving progressively eastward and dying out in northeastern Siberia around 14,000 years ago. Woolly rhino breeding numbers increased gradually starting around 1 million years ago and, by about 152,000 years ago, reached a peak of roughly 21,000 animals.