Most of us know, vaguely, that we all come from Africa. East Africa, it turns out. How we got from there to here is another matter.
“The Human Family Tree,’’ airing tomorrow on National Geographic Channel, tells us when, where, and how humanity spread from Africa across the globe. Kevin Bacon, a marvelous, low-key narrator, follows the migrations, backed by the effective use of computer maps showing the various “capillaries’’ of human movement to the Middle East, central Asia, southeast Asia and Australia, Europe, and South America.
The two-hour program is built around the National Geographic Genographic Project, where project director Spencer Wells and his team spent four years traveling across the world gathering DNA information with simple cheek swabs from some 350,000 people of diverse backgrounds.
What he found was that we’re 99.9 percent the same. And despite the migrations from Africa, the continent remains the most genetically diverse population in the world.
The scale of this project is unprecedented, although Harvard Professor Henry Louis Gates Jr. covered some of the same ground using DNA tracing for his PBS series “African American Lives’’ in 2006. Such exploration would not exist absent the cutting-edge advances in our genetic understanding.
Visually, “The Human Family Tree’’ is strong. There are re-creations of our ancestors in various locations around the world that help us better understand what was going on, and Wells’s travels are lavishly shot on location around the world. Yet the show overwhelms us with cascading numbers - the thousands of years when someone went somewhere - and it is at times repetitive.
Ingeniously, Wells and producer-director-writer Chad Cohen focus on a neighborhood in Queens, a part of New York City with a polyglot population, to tell the story.
The team drew swabs from a couple of hundred people chosen randomly during a street fair one day.
We hear from a Turkish couple, a Thai, a Greek, a Slovenian, and more. Wells then traces their roots with surprising results.
David Reed, a young black model, only knew that his forebears arrived from Africa as slaves. Wells traced some of his DNA back to what is now Tajikistan, where his forebears grew paler because of the lack of sunlight. Later, they entered Europe. Reed was astounded and captivated to learn this.
According to “The Human Family Tree,’’ it all began 60,000 years ago in East Africa, when our forebears began to leave the continent - possibly due to weather changes. One group crossed the 17 miles of water to the Arabian peninsula and from there spread out. Some stayed in the Middle East. Others moved east on a southern route into Southeast Asia and Australia.
Another group went north to the mountains of Central Asia and eventually arrived in Europe. Still another took the longest, hardest route: the northern route to Siberia, where its people crossed into North America on the land mass joining the two continents at the time and made it down to Chile.
At the end of the program, Wells gathered together the people in Queens who gave cheek swabs. He initially divided them into five groups, based on their geographical roots. He then folded them into four groups, down finally into one group.
The feel-good conclusion of the show is we’re one big family, so why can’t we get along? A sweet question. Tell that to Greeks and Turks, Indians and Pakistanis, Arabs and Israelis. It’s enough to know our true roots without succumbing to wishful thinking.
Sam Allis can be reached at allis@globe.com 
