Everyone alive may share an ancestor who lived only about 2,000 years ago
Mitochondrial Eve and Y-chromosomal Adam lived tens of thousands of years apart and far back in prehistory. But a mathematical model by Joseph T. Chang, Douglas Rohde and Steve Olson suggests the most recent person from whom every living human descends could have lived as recently as 2,000 years ago, probably somewhere in East Asia.
A most recent common ancestor, or MRCA, is the latest individual from whom every member of a group is thought to descend. Biologist Richard Dawkins called such figures concestors, and in The Ancestor's Tale he walked back through 40 of them, from the human and chimpanzee split all the way to the ancestor we share with bacteria. The last universal common ancestor of all life dates back an estimated 3.5 to 3.8 billion years, while the common ancestor of cats, dogs and other carnivores dates to about 42 million years ago.
Genes let scientists trace single lines. Mitochondrial DNA passes almost unchanged from mother to child, and the Y chromosome passes from father to son, so each can be followed back to one person. Mitochondrial Eve is placed around 200,000 years ago, and a March 2013 study put Y-chromosomal Adam between 237,000 and 581,000 years ago. Those two were not a couple, and they need not have met.
The genealogical MRCA, reached through any mix of mothers and fathers, must be far more recent, because following both parents converges much faster than following a single gene. It cannot be found in DNA, since most ancestors' DNA vanishes from their descendants within a few hundred years, so it is estimated with models and simulations. Chang's work suggested candidate homelands near isolated populations, such as the Chukchi and Kamchatka peninsulas, Indonesia and Malaysia, or Taiwan and Japan. Had Europeans never reached the Americas and Australia, that ancestor would be only about 2.3% further back.
The idea is counterintuitive. Sharing an ancestor does not mean inheriting their genes: after 32 generations, a single forebear's share shrinks to around 2 to the power of minus 32, less than one DNA letter. The MRCA was simply someone whose descendants spread everywhere, not a bottleneck or a first couple.
Source: Most recent common ancestor
