New Delhi, June 25 -- For years, scientists have pondered the reasons behind humanity's successful spillover from Africa to Eurasia and beyond. Various hypotheses have been suggested, ranging from interbreeding between different groups of humans to technological innovation. Now, a new study says it was humans' successful spread within the African continent itself that helped them win the rest of the world.

This happened around 70,000 years ago. Humans spread out into the Sahara and the Sahel, the dry scrublands that separate the world's largest desert from the green equatorial forests of sub-Saharan Africa. Humanity spread out in the latter climes as well.

A team of scientists assembled a dataset of archaeological sites and environmenta...