A three-generational tree is focused, as it helps you highlight the most impactful relationships and is easy to follow.

What This Unprecedented 13-Million-Person Family Tree Reveals For starters, the new tree calls into question a prevailing theory for why people stopped marrying close relatives.

The 'Genome Hacker' Who Mapped a 13-Million-Person Family Tree Huge crowdsourced genealogy databases are inspiring new genetics research.