Likewise, they were drawn to "Lady" Thelma Short Doswell whose historical research was the basis of both family trees.
Doswell, a certified genealogist whose mother was a Blackwell, acted last night as sort of a "griot" - the West African term for a village elder who is the keeper of oral history.
Doswell is a plain-talking, direct woman of "over 65 years."
Last night she dispensed advice to awed participants, and described how she began compiling the Blackwell geneaology in 1952 based on the recollections of an aunt who was 109 years old.
"The oral history was my foundation," said Doswell, a widow who lives in Hyattsville, Md.
"Then I went to the record and it took about two years to finish. There's 3,333 names there."
The conference, at the International House, 38th and Chestnut streets, is sponsored by the city's Coalition of African American Cultural Organizations Inc., and is part of the Black History Month celebration.
Participants can attend reunion workshops and panel discussions today, and a family ecumenical service will be held tomorrow.
Doswell was invited to the conference by JoAnne Blackwell Winborne, a native Philadelphian who now lives in Pennsauken, N.J.
When asked just how they were related, Winborne, 40, paused and thought for a few seconds.
"Ask Thelma," she said, slightly embarrassed.
"Her great grandfather and my great grandfather were brothers," Doswell said after a moment's calculation.
"Am I right? . . . Yeah," she said with a smile.
Doswell, who has appeared on television talk shows and has been the subject of numerous newspaper articles, said the Blackwells' oral tradition was found to be "about 95 percent accurate" when compared with family records.
The Blackwell genealogy, she said, started with Ama, a West African, who was brought on the slave ship Doddington to Yorktown, Va.
Plantation owner James Glenn Blackwell bought Ama and later gave her to his son Robert, who started a plantation of his own, said Doswell.
Ama had a daughter, Tab, who married Odofo, another West African, and they begat . . .
The names branched and flowed all over the canvas. Among the names was that of tennis star Arthur Ashe Jr., who Doswell said has attended Blackwell reunions.
The family's reunions occur every fourth Saturday in October in various places in the South and the Northeast. One, in Baltimore a few years back,
drew about 1,300 family members.
Last night, two Mount Airy cousins, Connie Lowber and Skip Fleming, asked Doswell for tips on how to get their own fledgling reunion efforts off the ground.
The problem, said Lowber, 48, was they had had two reunions and, well, there were some organization kinks that needed ironing out.
Doswell, who gives families advice on organizing reunions, listened and offered Lowber a few suggestions.
Iona Vargus, who is dean of Social Administration at Temple University and studies family traditions, said last night that "values get passed down the generations (at reunions)."
Reunions, Vargus said, stress "identification that comes through finding missing links. It's also role modeling and encouraging kids to achieve."