David said he was reluctant to have personal details disclosed on TV but was glad he finally took part, lauding the 'incredible job' done by researchers.
There were other revelations that took him aback, he said. David learned of ancestors who settled in Birmingham, Alabama, in the 1840s, owned two slaves and fought for the Confederacy in the Civil War.
A hundred years later, many aunts, uncles and cousins on the maternal side of his family died in Nazi Germany's Holocaust.
But Finding Your Roots is aimed at more than satisfying individual curiosity and telling an engrossing story, said Gates, an executive producer and writer as well as host of the series.
It carries a message of shared origins that he argues can benefit society.
The science of DNA proves that 'there aren't four or five biologically distinct races. We're all from one race, the human race, genetically,' Gates said.
'And we know that genetically we all descended from common ancestors that left the African continent 50,000 years ago. That's a fact.'
Detailing how different ethnic groups contributed to world history and how their experiences 'merged or conflicted' with those of other groups is also of immense value, he said.
'It's part of a larger education process to make us all realize we're fully human,' Gates said.