The mammoth herd approaches the rushing river. A calf ambles close to her mother�s huge legs, brushing their long, glossy hair now and then with her trunk. The sky is brilliant blue, and a dry wind hisses through the grasses, which billow like oceanic swells across a steppe 10,000 miles wide, spanning the northern arc of the Ice Age world. The long winter is over; birdsong and the scent of damp loam fill the air.