studies considered the 10% estimate for aurochs gene flow a gross overstimate and based on flawed data, and not supported by the data from the full nuclear genome of the wisent. Some of the authors however support the hypothesis that similarity of wisent and cattle (Bos) mitochondrial genomes is result of incomplete lineage sorting during divergence of Bos and Bison from their common ancestors rather than further post-speciation gene flow (ancient hybridisation between Bos and Bison). But they agree that limited gene flow from Bos primigenius taurus could account for the affiliation between wisent and cattle nuclear genomes (in contrast to mitochondrial ones). Alternatively, genome sequencing completed on remains attributed to the Pleistocene woodland bison (B. schoetensacki), and published in 2017, posited that genetic similarities between the Pleistocene woodland bison and the wisent suggest that B. schoetensaki was the ancestor of the European wisent. However, other studies have disputed the attribution of the remains to this species, otherwise known from remains hundreds of thousands of years older, instead referring them to an unnamed lineage of bison closely related to B. bonasius. A 2018 study proposed that the lineage leading to the wisent and to the lineage ancestral to both the American bison and Bison priscus had split over 1 million years ago, with the mitochondrial DNA discrepancy being the result of incomplete lineage sorting. The authors also proposed that during the late Middle Pleistocene there had been interbreeding between the ancestor of the wisent and the common ancestor of Bison priscus and the American bison. Behaviour and biology Social structure and territorial behaviours The European bison is a herd animal, which lives in both mixed and solely male groups. Mixed groups consist of adult females, calves, young aged 2–3 years, and young adult bulls. The average herd size is dependent on environmental factors, though on average, they number eight to 13 animals per herd. Herds consisting solely of bulls are smaller than mixed ones, containing two individuals on average. European bison herds are not family units. Different herds frequently interact, combine, and quickly split after exchanging individuals. Bison social structure has been described by specialists as a matriarchy, as it is the cows of the herd that lead it, and decide where the entire group moves to graze. Although larger and heavier than the females, the oldest and most powerful male bulls are usually satellites that hang around the edges