Dry grasses rustled as we carefully skirted the gorge of Ethiopia’s biggest river, the rumbling, crashing sound of the water far below rising as we neared the edge, where a dirt track led several hundred metres down to flatter ground adjacent to the river itself. The light was already very low and fading quickly, as we were only 9 degrees north of the equator. Unseen animals lurked in the thorny scrub alongside our trail. . . .