AP Photo

The ability to control fire marked a major milestone in human evolution, helping our ancestors stay warm in the cold, enhance the nutritional value of their food and keep predators at bay, among other uses. But exactly when humans mastered flame has proved difficult to establish. The oldest signs of fire in association with human activity date to around 1.5 million years ago, but because they come from open-air settings (as opposed to caves), the possibility exists that they represent wild fires instead of anthropogenic ones.