They didn’t like being out of Africa. Scientists have sequenced DNA from a 4,500-year-old skull found in an Ethiopian cave, revealing new clues in the mystery of humans’ global migration. The Mota Cave man boasts pure African DNA, meaning his ancestors never left the continent. More modern African genomes show a mix of Eurasian ancestry, suggesting a huge backflow migration roughly 4,000 years ago. But scientists still have one bone to pick: deciphering exactly why 25 percent of the Eurasian population packed up and moved back to Africa.