Modern humans arose after 2 distinct groups in Africa mated over tens of thousands of years

A Nama girl in Northern Cape province, South Africa. She wears a white shirt and a black skirt with white spots. She sits on the rocky ground in front of a small mountain in the background.

Modern humans arose after a complex history of intermingling between ancestors on at least two different but closely related evolutionary branches, a new study suggests. 

While these genetically distinct branches had divided, people on each branch continued to occasionally mix over time, the researchers found.