Life at the Extremes

The introduction opens with a tragedy from November 1999. Golf champion Payne Stewart and four others die aboard a Learjet: at about 11,300 metres the cabin loses pressure, the passengers die of lack of oxygen, and the plane flies on autopilot until its fuel runs out. From this the author draws her central idea: every day, mostly without noticing, we live on the edge of life. We fly at heights where life is impossible, swim in icy water and go diving. The book's questions follow: what happens when a freezer door locks behind you, when you are trapped under ice, or when you are stranded in a desert without water?

The most honest part of the introduction concerns experiments on people. Physiologists first tested the dangers on themselves; the famous scientist J. B. S. Haldane said he had been his father's guinea pig since the age of four and went on to become a distinguished physiologist himself. But the author does not hide the dark side: Nazi experiments at Dachau, experiments on prisoners of war, and in the West, condemned prisoners who «volunteered» in exchange for a stay of execution. Ashcroft writes plainly that this was no real choice.

The Kilimanjaro essay contains the book's most personal pages. Starting in tropical rainforest, the author climbs through giant plants and spends a sleepless night with a headache at 4,600 metres. The climb up the volcanic cone begins at two in the morning, three steps up and two sliding back. The strongest member of the group collapses on the way and has to turn back, showing that no one can predict whom mountain sickness will strike.

Chapter one opens with a question: if you were lifted from sea level to the summit of Everest in one go, you would lose consciousness within seconds. So how did Peter Habeler and Reinhold Messner climb it without oxygen? To answer, the author turns to history. A Chinese source from the first century BC tells of men and animals suffering headaches and vomiting on the «Great Headache Mountain» and «Little Headache Mountain». In 1590 the Spanish priest José de Acosta described air in the Andes «so thin that however much you breathe in, it is not enough».

Midway through the chapter the author marks the limits of where people can live. About 15 million people live in high mountain regions, mostly in the Andes, the Himalayas and Ethiopia. The highest permanent human settlement is a miners' camp at 5,340 metres on Aucanquilcha in the Andes; although the sulphur mine lay at 5,800 metres, the miners preferred to climb an extra 460 metres every day rather than sleep higher. It was the French physiologist Paul Bert who first showed that lack of oxygen is the main cause of mountain sickness, using a pressure chamber big enough for a person, which he built at the Sorbonne.

The most fascinating pages concern the Incas and the Spanish. The Incas had two armies: one was kept permanently at altitude to stay acclimatised, the other fought on the coast. The Spanish built the city of Potosí at 4,000 metres, but their babies died within two weeks of birth; the first Spanish child to survive, born on Christmas Eve 1598, fifty-three years after the city's founding, was hailed as a «miracle». Then come the balloonists. In 1862 the meteorologist James Glaisher passes out, and Henry Coxwell, his hands useless, pulls the valve cord with his teeth to bring the balloon down.

• A structure that blends personal experience with history and scientific explanation
• Attention to the colourful people behind the discoveries
• Clear prose that unpacks complex physiology with everyday examples
• A tone that tells tragedies without sensationalism, as lessons