The climate during the Pleistocene Epoch (2.6 mill – 11,700 YA) fluctuated between episodes of glaciation (or ice ages) and episodes of warming, during which glaciers would retreat. It is within this epoch that modern humans migrated into the European continent at around 45,000 years ago. These Anatomically Modern Humans (AMH) were organized into bands whose subsistence strategy relied on gathering local resources as well as hunting large herd animals as they travelled along their migration routes. Thus these ancient peoples are referred to as Hunter-Gatherers. The timing of the AMH migration into Europe happens to correspond with a warming trend on the European continent, a time when glaciers retreated and large herd animals expanded into newly available grasslands.
Evidence of hunter-gatherer habitation has been found throughout the European continent from Spain at the La Brana cave to Loschbour, Luxembourg and Motala, Sweden. The individuals found at the Loschbour and Motala sites have mitochondrial U5 or U2 haplogroups, which is typical of Hunter-Gatherers in Europe and Y-chromosome haplogroup I. These findings suggest that these maternally and paternally inherited haplogroups, respectively, were present in the population before farming populations gained dominance in the area.
Based on the DNA evidence gathered from these three sites, scientists are able to identify surviving genetic similarities between current day Northern European populations and the first AMH Hunter-Gatherers in Europe. The signal of genetic sharing between present-day populations and early Hunter-Gatherers, however, begins to become fainter as one moves further south in Europe. The hunter-gatherer subsistence strategy dominated the landscape of the European continent for thousands of years until populations that relied on farming and animal husbandry migrated into the area during the middle to late Neolithic Era around 8,000–7,000 years ago.