Editor’s Note: Call to Earth is a CNN editorial series committed to reporting on the environmental challenges facing our planet, together with the solutions. Rolex’s Perpetual Planet Initiative has ...

Photographs of a 1930 expedition to Uganda, Eastern Belgian Congo [Democratic Republic of Congo], and the Sudan to collect zoological and botanical specimens for the British Museum of Natural History.

It was a vast, unwieldy expedition. Three giant inflatable rafts, two watercraft jets, six rubber dinghies, eight Land Rovers and six Range Rovers, 89 tons of gear, and one Beaver aircraft which was ...