The pattern of dispersal of humans out of Africa occurred in four distinct waves over the past 125,000 years, reports a study published online this week in Nature. These migration events were driven by climate change connected to variations in Earth’s orbit.

Previous studies proposed that climatic changes due to variations in Earth’s orbit during the Late Pleistocene epoch (126,000 to 11,000 years ago) have influenced the timing of dispersal of Homo sapiens out of Africa. However, sparse palaeoenvironmental data in key regions and uncertainties in climate simulations and in the dating of fossil and archaeological records have hindered progress in this field.

Axel Timmermann and Tobias Friedrich constructed a numerical model that quantifies the effects of past climate and sea-level change on global human migration patterns over the past 125,000 years. The model identifies prominent glacial migration waves across the Arabian Peninsula and the Levant region around 106,000-94,000, 89,000-73,000, 59,000-47,000 and 45,000-29,000 years ago. These results are in close agreement with archaeological and fossil data.

The findings document the key role of orbital-scale climate changes in shaping global population distributions. Conversely, abrupt, millennial-scale climate changes are shown to have a more limited, regional effect. The model also shows an almost simultaneous early arrival of Homo sapiens in southern China and Europe about 90,000-80,000 years ago.