New Scientist: Modern humans’ expansion across the planet has been linked to climate by Andrea Manica, a geneticist at the University of Cambridge, and colleagues. They teamed up with climate modelers to simulate the changes in Earth’s temperature and rainfall over the past 120 000 years and thus determine the amount of food available and which regions would have been habitable by humans. Homo sapiens originated in Africa some 200 000 years ago, for example, but left the continent only about 70 000 years ago. The researchers determined that the desert conditions of the Arabian peninsula trapped early humans on the African continent. But when the peninsula began to receive more rain, it became more fertile, and humans were able to cross it and spread into Asia. Other climate effects, such as lowering sea levels and receding ice sheets, allowed humans to continue to spread onto other continents. The team’s findings, which were published in the Proceedings of the National Academy of Sciences, are consistent with fossil and archaeological records.