It is generally accepted that the first fertility increase occured in the Neolithic, during the process of the so-called Neolithic Demographic Transition. But this hypothesis is not based on biological skeletal evidence of fertility, but rather derived from indirect evidence. In order to provide direct evidences about female fertility ERC BIRTH project investigates "crisis lines" which correspond to stressful life events and are visible in tooth cementum. We compare number of "crisis lines" in Mesolithic and Neolithic females from the Balkans (10000-5000 BC) in order to investigate whether the number of stressful events increased with Neolithic as a possible consequence of increase of fertility.