Maggie, a 55-year-old chimpanzee at the San Francisco Zoo, died from lymphoma just before her 56th birthday. She was known for her colorful blanket nests and subtle matriarchal role within the troop.

Scientists have long thought intelligence tends to develop through social interactions with an animals’ own species.

In nature, interactions between species are often framed in terms of survival - those that hunt and those that are hunted. But research is showing ...