As England's footballers struggle to deal with the effects of altitude on their bodies ahead of their first World Cup match in South Africa, they may wonder how people living day in day out at even higher levels get by at all.
A new study published this week in PNAS reveals that natural selection has enabled humans to better cope with living in Shangri La.
Shangri La here is not the mythical Eastern earthly paradise, but the very real province high up in the Tibetan plateau where the indigenous population lives at altitudes of 3,200m to above 4,000m – much greater than the 1500m Gerrard, Lampard and the rest will be playing at on Saturday.
The international team of researchers from the UK, Ireland, China and the US searched for evidence of selection at the genetic level among people living at these high altitudes where there is so little oxygen.
The study’s corresponding author, Professor Peter Robbins of Oxford’s Department of Physiology, Anatomy and Genetics, confirms that ‘Tibetans are better equipped for life at high altitude.’
People who move to live at high altitudes tend to be at risk of a chronic mountain sickness. The body makes too many red blood cells, giving excessive levels of haemoglobin, in an attempt to capture the little oxygen there is in the air. But native Tibetans manage to remain unaffected.
So the scientists compared the genetic profiles of groups of Tibetans living at these high altitudes with nearby populations in lowland China, and they found changes in a single gene were present at high frequency among the Tibetans.
The researchers showed that having a different version of the EPAS1 gene gives Tibetan populations an advantage: it keeps levels of haemoglobin low and so protects them against developing chronic mountain sickness. ‘This is where individuals make too many red cells and the blood becomes very sticky,’ says Peter Robbins. ‘[Having the EPAS1 variant] may also help with reproductive fitness at high altitude, but that is more speculative.’
This is good evidence that the lack of oxygen at these altitudes has exerted an evolutionary selection pressure over the 10,000 years or more people have been living in these areas.
‘There are probably not more than a handful of definitive examples of human evolution to their environment at the genetic level that have so far been described,’ says Peter Robbins. ‘There are genes for variation in skin colour, certain genes that confer protection against malaria (for malaria infested environments) and possibly one or two dietary adaptations (but these are a bit more speculative).’
There may also be some pay off from this work for future English footballers (or, depending on the result, fewer excuses):
EPAS1 – also known as HIF2a (hypoxia-inducible factor 2) – is a major gene involved in keeping oxygen levels stable, explains Peter Robbins. ‘As oxygen transport is the principal limiting factor to much endurance exercise, everything we can understand in relation to human variation here will probably help us to understand better the constraints on athletic performance.’
‘In addition, as low oxygen (hypoxia) is a feature of so much disease (eg lung disease, heart disease, vascular disease, cancer), understanding human variation in the response to low oxygen may help us to understand why some people seem so much better at surviving conditions of low oxygen than others.’