Researchers observed three chimpanzee communities of the Tai National Park. They kept full demographic records and collected fecal samples to conduct paternity tests on all new community members, for up to 30 years. Catherine Crockford, the lead author, says: "When we study our closest living relatives, like chimpanzees, we can learn about the ancient environmental factors that made us human. Our study shows that a mother's presence and support throughout the prolonged childhood years was also likely a trait in the last common ancestor that humans shared with chimpanzees six to eight million years ago. This trait is likely to have been fundamental in shaping both chimpanzee and human evolution".