I n many ways, the last two northern white rhinos on Earth spend their days as if they were not the last two northern white rhinos on Earth. They lumber majestically along a dun and dusty landscape, as their ancestors have done for millions of years. They graze with dedication on tremendous amounts of grass — more than 100 pounds a day — uprooting the plant with the flat, powerful lips that evolution painstakingly bestowed. They wallow in the mud, or rest in the shade of acacia trees, or gaze,