Gombe’s terrain is extremely rugged. The vegetation is tangled and thick; steep ridges rise abruptly from the lake, as much as 2,500 feet in just a mile and a half. The park cannot be reached by road, and its borders are a long walk from any village. These features make the preserve an Eden for chimpanzees, while mostly keeping people at bay. But Goodall had chosen — for my sake, perhaps, because as recently as two years ago she was still clambering over steep soggy slopes, pulling herself up with a vine — an easy path. Twenty minutes later, we reached a stream, and an odd moment ensued: Should I help her with her footing? An octogenarian in my company was walking on slippery rocks, wearing sandals no less. I crossed ahead of her and stood on the other side, waiting for her to hold a hand out; she did not.