The spread of certain types of grasses throughout southwest Africa between 8 and 3 million years ago was aided by a combination of wildfire and increasing aridity, reports a paper published online this week in Nature Geoscience. These grasses, known as C4 grasses, are today the dominant grass type in tropical regions of Africa.

Sebastian Hoetzel and colleagues analysed a marine sediment core collected off the coast of Namibia for pollen and other plant material, as well as for chemical tracers of past fire activity. They find that the emergence of the then newly evolved C4 grasses coincided with a period of high fire activity and increasing dryness. The authors suggest that more frequent wildfires promoted the spread of these grasses, which they say were better adapted to recovering in burnt areas.