Hundreds of thousands of years ago—when people still lived in small hunter-gatherer bands, when it’s not even clear they were totally anatomically modern (though they probably were)—something happened in the human genome.
Somewhere in Africa, a man carried a Y chromosome that would turn out to be the only surviving Y chromosome in humans today. This man lived around plenty of other people, perhaps with their own Y chromosomes, but chance whittled away his peers’ contributions until only his was left.
In a totally independent event, a woman carried mitochondria—tiny structures contained inside cells—that would become the only mitochondria people have today. Like the Y-man, she lived around other people, but over thousands of years, luck struck down all others’ mitochondria save her own.
Now, in a pair of new papers published today, two separate research groups say they’ve determined the dates during which the last common Y-chromosome ancestor lived. One of the groups also came up with dates for when the last common mitochondrial ancestor lived. The dates vary from previous estimates—and from each other—which is sure to set off healthy debates about when these seminal genetic events occurred.