Alison Jolly, an American-born primatologist whose research in the forests of Madagascar shed new light on the evolution of social intelligence and helped disprove a longstanding scientific tenet that males were dominant in every primate species, died on Feb. 6 in Lewes, East Sussex, England. She was 76.

The cause was breast cancer, said Barbara Orlando, a longtime friend.

Dr. Jolly’s two major insights emerged from her 1960s field studies of the lemur, a primate whose development in relative isolation on the island of Madagascar makes the species something akin to a living fossil.

Writing in the journal Science in 1966, Dr. Jolly cited lemurs’ complex social relationships as evidence of an unexplored trail in one of anthropology’s great mysteries: the evolution of higher intelligence. She suggested that the many hours lemurs spent in play, mutual grooming and networking — activities that establish social ties and hierarchies — may have been as important to the evolution of intelligence as the development of weapons and tools, then considered the hallmark of evolutionary advance.

More unnerving to colleagues was her discovery that in some primate species, females run the show. The finding upended a bedrock assertion in evolutionary biology, based on studies of chimpanzees and orangutans in captivity, that males dominated females in every primate species, including humans.