One of the greatest uncompensated land mammal extinctions has occurred at or near the end of the Pleistocene. The causes of this extinction remain debatable for a long time as they failed to demonstrate a direct dependence of Pleistocene mammals population size and/or number on any natural/anthropogenic factors. Recently the first evidence of this kind has appeared due to the quantitative and qualitative progress in 14C dating. We have 14C dated hundreds of mammoth remains from Arctic Siberia believed to be one of the last refugium for the Pleistocene megafauna before the final extinction. The analysis of these and of many earlier published dates shows that under certain conditions the number of 14C dates reflects the relative number of animals. Considering this pattern, we managed to reconstruct the fluctuations of Arctic Siberia mammoths number during the last 50000 years. These numbers changed cyclic with the period of oscillation close to 5000 years keeping downward trend. During the last 25000 years the number of mammoths have dramatically reduced thrice. The last mammoths inhabited New Siberia Island (which was the part of a mainland at that time) 9470±40 radiocarbon years ago.
The obtained estimate of the relative number of mammoths has allowed a direct search of the clues to the depopulation and extinction of mammoths. We compared a curve of change of mammoths number with high-resolution record of Late Pleistocene paleoenvironmental changes in Arctic Siberia. This comparison has shown that number of mammoths essentially depended on the temperature and humidity of the climate. This is the first direct evidence of the Pleistocene mammals reaction on changing environmental factors. The unfavorable combination of temperature and humidity at the beginning of the Holocene have reduced number of animals and the size of mammoths population up to a critical level, pushing mammoths to the extinction. The dispersal of humans to the Arctic Siberia in the Late Pleistocene, not later than 28000 years, was not essentially affected the number of animals that excludes the overkill hypothesis. However, presence of people, apparently, was fatal to mammoths during periods of critical reduction of their number, one of which took place at the beginning of Holocene.