In 2021, DNA older than a million years was sequenced for the first time, from two mammoth teeth of Early Pleistocene age found in eastern Siberia. One tooth from Adyocha (1-1.3 million years old) belonged to a lineage that was ancestral to later woolly mammoths, whereas the other from Krestovka (1.1–1.65 million years old) belonged to new lineage, possibly a distinct species, perhaps descended from steppe mammoths that had became isolated. The study found that half of the ancestry of Columbian mammoths came from the Krestovka lineage, and the other half from woolly mammoths, with the hybridization happening more than 420,000 years ago, during the Middle Pleistocene. Later woolly and Columbian mammoths also interbred occasionally, and mammoth species perhaps hybridized routinely when brought together by glacial expansion. These findings were the first evidence of hybrid speciation from ancient DNA.