Gradual climatic warming and increased humidity gave rise to fundamental changes in the natural environment. In the European Lowlands this period (known as the Mesolithic) witnessed the expansion of mixed woodland, rich in numerous varieties of edible plants and game animals similar to contemporary species. The widespread availability of food resources ensured the survival of increasingly larger groups of people, whose main subsistence strategies were foraging, hunting, fowling and fishing. New environmental conditions dictated changes in the way of life and organisation of human societies. Instead of seasonal hunts in large groups, which involved travelling over substantial distances, hunting was now carried out in the local surroundings by smaller groups or individuals. This led to a more stable and settled existence and meant that human communities grew used to living in a given territory. Mesolithic populations, limited numbers of whom reached Greater Poland from the north and west, preferred to build their settlements in topographically diverse areas with a good network of watercourses. It is from the Mesolithic period that we have the earliest evidence in this region for ritual burials, which attest to an elaborate death cult and belief in the afterlife.