Gorilla Mafia? Groups Ruled by Related Males, Study Says

John Pickrell in England
for National Geographic News
March 31, 2004

New genetic findings reveal that ruling dynasties may monopolize leadership of many neighboring communities of Africa's western gorillas—like a primate version of the Mafia.

Paternity tests reveal that leaders of adjacent western lowland gorilla territories in Africa are closely related as fathers, sons, and brothers.

The results, detailed in the current issue of the science journal Current Biology, may help to explain curiously peaceful interactions among neighboring social groups. The groups were observed in new behavioral studies of the western lowland gorilla (Gorilla gorilla gorilla).

The study could also provide clues about the role and development of kinship in early human society, say researchers behind the work.

Despite being the most numerous kind of gorilla, the western lowland gorilla species is the shyest and least understood. Up to a hundred thousand western lowland gorillas are thought to inhabit the forests of central Africa.

Aggressive Interactions

Most knowledge of gorilla behavior comes from studies of the eastern mountain gorilla (Gorilla beringei beringei), found mostly in Rwanda and Uganda. In that species several reproductively active mature males (silverbacks) may remain within the group in which they were born for life. And among the eastern mountain gorillas, it is the females that migrate when mature.

Competition among eastern mountain gorilla groups for females can therefore be fierce, and levels of aggression among males in neighboring mountain gorilla groups can be extremely high.

Studies have revealed that male mountain gorillas engage in displays of aggression over 90 percent of the time when neighboring groups come in close contact, said geneticist Brenda Bradley at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. These spectacular male-to-male displays often involve chest beating, charging, and hooting. One in five displays may culminate in physical violence, she said.

"That's why recent behavioral studies of western gorillas were really surprising," said Bradley, who is lead author of the new study.

Co-author Diane Doran-Sheehy, of the State University of New York in Stony Brook, has carried out pioneering studies of one of the very first groups of western gorillas that was habituated to human presence.

Studying lowland gorillas has proved more difficult than studying their mountain counterparts. The dense, flat forests that lowland gorillas call home do not provide them the long-range visibility that allows mountain gorillas to spot researchers from afar and slowly get used to their presence.

Continued on Next Page >>




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