The roof of the world, north of the Himalayas, stretches over two and a half million square kilometres. It is inhospitable, arid and permafrosted. When it rains, it mainly hails. It’s the highest place on the planet where you can stand on flat ground and be near the heavens, and standing there will thicken your blood. Unless you carry the EPAS1 gene.
This gene stops you over-producing haemoglobin – the oxygen-carrier in red blood cells. Too much haemoglobin raises blood pressure and, with it, the risk of stroke, among other bloody things.
This gene came from an ancient, extinct subspecies of human called the Denisovans. We know this because scientists sequenced Denisovan DNA four years ago. This DNA came from a fragment of a pinky and two teeth found in a cave.
The ancestors of today’s Tibetans had sex with Denisovans. Genes were passed around. The useful ones remained. This allows Tibetan people to survive on the roof of the world.
I wrote about the science for this week’s BioNews. Have a read.