Carol Beckwith and Angela Fisher have traversed 44 of Africa's 54 countries over four decades, documenting rituals used to mark milestones such as birth, death, and courtship, the graduation of girl to woman or the moment a warrior becomes a respected elder.
Now their archive - comprising more than a million images, hundreds of artefacts and field diaries, and thousands of hours of video - is looking for a home.
They want the collection to go to a university in Africa or some other venue that will guarantee access to African artists, historians and researchers.
"This record of Africa won't be taken again. It can't be taken again because 40 percent of it is already lost," said Fisher, a vivacious Australian draped in beads and red chiffon for their book launch in Nairobi on Sunday.
Heat lightning flashed across the sky as models, acrobats and dancers showcased traditional music and textiles at the event at Africa Heritage House, a private museum. But conflict, climate change, and the spread of technology are erasing or transforming many such customs.
LOSS OF IDENTITY
In South Sudan, decades of war has devastated traditional Dinka culture, said Beckwith, a petite, curly-haired American. Few now can make the beaded corsets whose patterns and colours would tell you the life story of its wearer.
In Ethiopia, desertification and land grabs are pushing nomads south into farming lands or towns. Samburu elders in Kenya worry that youngsters enamoured of cell phones and city life no longer care for time-consuming social ceremonies and the obligations they entail.
"It's really important for change to happen, but ... in a way that works without losing your identity," said Fisher.
Encouraged by conservationists, one Maasai community in Kenya changed from lion-hunting to athletic games as a way of proving male prowess, she said. The Wodaabe people in Niger still stage male beauty pageants famed for their use of make-up and grimaces.
The photographers' friend Nike Okundaye, a Nigerian chief and textile artist, is trying to revive the laborious methods for dying patterned indigo clothes, a tradition handed down from her great-great-grandmother.
Women once used the cloth - Nigeria's "colour of love", Okundaye says - to flaunt matrimonial harmony. But the months-long process to produce a piece makes it too expensive for most consumers, so now her work hangs in Washington's Smithsonian Museum and is pictured in the pages of Beckwith and Fishers' books. Okundaye has been working with them since 1967, she said.
"Carol loved the culture and Angela loved the tradition," Okundaye said. "We hope their photographs will inspire a new generation."