Which is the longest mountain range on land?

The Andes, about 7,000 kilometres down the western edge of South America through seven countries - and on land is the necessary qualifier, because the mid-ocean ridge system runs for some 65,000 kilometres and is nine times longer, almost all of it underwater and unmapped in detail until the twentieth century.

The Andes are being pushed up by the Nazca plate sliding beneath the continent, which is also why the region has the volcanoes and the earthquakes - the largest ever recorded, magnitude 9.5, struck Chile in 1960 and produced a tsunami that killed people in Japan a day later.

The range has shaped the people on it physically. Andean populations carry adaptations to thin air - notably higher haemoglobin concentration - which is a different solution from the one Tibetans evolved, and the Tibetan variant appears to have been inherited from Denisovans. Two populations, two mountain systems, two entirely separate genetic answers to the same problem, which is about as clean a natural experiment in human evolution as exists.