Mitochondrial DNA, which is only passed on by mothers, is the focus of many studies of ancient human migration. While we get much of our DNA from both parents, which results in a mash-up that’s difficult to untangle while tracing the roots of a family tree, your mitochondrial DNA tells a single story: that of your mother, and her mother, and her mother’s mother. That creates a record that’s easier to track back in time. Mitochondrial DNA also mutates much faster than the rest of our genetic material, creating generation-to-generation changes researchers can use to track movements and meetings between groups of ancient people. It’s a way of understanding genetic change over centuries, rather than over millennia, and many researchers think it gives a clearer picture of our species’ family tree.