The Centre Valbio research station, a modern building of stone and glass set in the jungled hills at the edge of Madagascar’s Ranomafana National Park, was starting to look like the third season of The Wire. Big tackboards lined the walls, each one covered with dozens of pinned-up photographs. Some images were grouped together in families, while others floated alone, unconnected. It was 2012, and Rachel Jacobs was using Detective McNulty-style tactics to sort out the associations in a very different kind of crew: the park’s population of red-bellied lemurs.