Tim Severin's book about the East Indonesian Spice Islands is blissfully free of Ginger Spice but full of insights as it retraces a journey through places of fabulous natural and cultural diversity by the first person to articulate evolutionary theory, Alfred Russel Wallace. In restaging parts of Wallace's perilous explorations, recorded in his enthralling The Malay Archipelago (1869), Severin repeats the formula of previous books and duplicates the earlier traveller's difficult conditions. Wallace's book "reveals a truly extraordinary man" who inspired Severin to monitor later changes in the Spice Islands and efforts to preserve their unique habitats. He condenses Wallace's 60 or 70 journeys over eight years into one continuous route and a few months.

Any book about Wallace would be a fascinating one. He was "a learned maverick" willing to think the inconceivable, a man of ability and modesty, possessed with phenomenal curiosity. Severin deserves credit for bringing us to him in this moving biography which is itself a work of exploration and witness.

The story of Wallace's life is interspersed with accounts of Severin's visits, in a traditionally built boat, around the remote islands east of Borneo, such as Sulawesi and the tiny Banda and Kei islands. Although the intensive logging and rapid industrialisation which have wrecked other parts of Indonesia and caused its current environmental catastrophe have barely reached them, Severin finds plentiful evidence of man-made disaster.

The bad news is very bad, and fulfils Wallace's worst prophecies. He was unequivocally hostile to commercial greed and the way in which imperialism mostly enriched "large capitalists". When he returned to Victorian Britain, he concluded that its vast inequalities had produced "a state of social barbarism". Severin makes more hesitant criticisms on finding economic and political conditions comparable to those Wallace condemned.

But there is also good news: here Severin begins to match Wallace for inspiration and commitment, so that his project really comes alive. Among sketches of jungle life, Severin assumes Wallace's enthusiasms and approach. Funded by sales of rare specimens, Wallace returned home with two live birds of paradise. But he was less fortunate than Severin (funded by BP) in his pursuit of the rare Red Bird of Paradise. Severin's account of watching those birds in their "dancing trees" is intoxicating, as is his witness of the sea turtle's struggle to lay its hunted eggs and the crew's efforts to hide them.

Remoteness is the best protection. He discovers that the trade in nutmeg maintains the Bandas' independence, and that villages on the Kei Islands retain their traditional lifestyle in equilibrium with the forest.

Indeed, Severin's conclusions invite links between the survival of ancient ways of life and the preservation of environmental diversity. A vital element is the ethical curiosity displayed here about other people and the cultural differences they represent. These lessons can seem intangible, but the value of Severin's book is that it makes them concrete, engaging and enjoyable. The Spice Islands Voyage should inspire new readers to discover the remarkable writings of Wallace himself.

Little, Brown, pounds 20