In an interesting case of convergent evolution, people living at altitudes over 4,000 metres in the Andes have been found to have independently developed almost the same genetic response to mountain sickness as the Tibetans. The two genetic groups are divided by history and geography.
Their gene mutations differ slightly and occurred 20,000 years and 18,000 km apart, but their effect is identical: they permit humans to flourish on thin air, reports a new paper led by Elijah S Lawrence in Science Advances, the journal of the American Association for the Advancement of Science. Interest in convergent evolution which adapts to hostile habitats is more than academic, as the human race braces for climate change.
The adaptations in Tibetans and Andeans involve changes in the EPAS1 gene, which is well-researched as a site of responses triggered by hypoxia, the main cause of mountain sickness. The responses include the production of more red blood corpuscles and changes to blood vessels, to deliver far better perfusion and oxygenation than in other humans.
Increased efficiencies in the transport and metabolism of oxygen allow the owners of these mutations to function well in high-altitude atmospheres in which other people suffer pulmonary and cardiovascular distress. In Tibetans, the effects are epigenetic (working through pathways outside the genome) and do not seem to involve the coding sections of the EPAS1 gene that determine which amino acids are expressed during protein synthesis. In the case of Andeans, the genetic changes are in a coding region of the gene ― they’re baked right into the genetic code.
Are the two populations, in the Himalayas and in the Andes, as unrelated as geography suggests? The Tibetans are understood to have derived their versions of the gene from the Denisovans, the hominins discovered in a cave in the Altai mountains in Siberia.
There is uncertainty because only fragmentary material evidence of the group has been found, much less than for Neanderthals, for instance. But it is not impossible to conceive that while some of the Denisovan population may have moved southwards from Siberia to leave genetic traces in India, others may have moved east across the now-submerged Beringia into the Americas.
The discovery that an EPAS1 variant in the Andes addresses hypoxia is both theoretically and practically important. Theoretically, because science creates its taxonomies by a process of comparing and contrasting, and opportunities are restricted among humans, who can only be compared with other humans.
The human sciences are likely to celebrate the hardest when space aliens finally contact us. The more different they are, the more opportunities they would provide to compare and contrast humans with. If aliens turn out to be very human, it would be a great relief for politicians and diplomats eager for a firm handshake, but a terrible let-down for scientists.
In the absence of space aliens, students of humanity and its products, like culture and technology, have been restricted to comparing human variants. Race is of two kinds. The kind discussed in opinion pages is a cultural and political construct based on ideas of intrinsic superiority and inferiority. It is imaginary and disgusting. But the other form of race is biological and very real.
Evolution has separated groups of people divided by history and geography into biological races with distinct responses to their environment. For instance, nut allergies are common in North America but very rare in South Asia. Cancer doesn’t afflict people from all racial groups the same way, and responses to treatment also differ.
For instance, Ewing’s sarcoma is typically a cancer of white boys, and rarely attacks coloured girls. Until the early 2000s, the medical and scientific literature dismissed race as “biologically meaningless”, but over time, it has come to be seen as a useful guide in medicine.
The discovery that two distinct races on separate continents have adapted to high altitudes at the same genetic site is significant. The only other instance of such an EPAS1 response is in the coelacanth, a type of lobe-finned fish. The ‘living fossil’—and a favourite expletive of Captain Haddock—from the early Devonian period was only etched in stone from its discovery in 1893 until 1938 when a live specimen was discovered in a fisherman’s catch in the Indian Ocean by the self-taught South African naturalist Marjorie Courtenay-Latimer. It is surmised that in the 400 million-year lifespan of the species, it had responded to an event which lowered oxygen concentrations in seawater.
Now that it is known that the EPAS1 gene is the device of choice for adapting to hypoxia, it must be of interest in an overcrowded planet. The peopling of the seas has been and will probably remain the stuff of science fiction because home economics is too expensive. In comparison, highlands freed of permanent ice look more inviting. The glaciers of the Third Pole are melting at an alarming rate and Pakistan has suffered unprecedented flooding as a consequence.
More disastrous climate and geological effects are bound to follow, but the process could also make highlands habitable for humans who can breathe thin air. And as governments and corporations develop a taste for manned space missions again―in which the volume of oxygen to be carried or generated is a limiting factor―people who flourish at high altitudes could be in demand.
There’s a political irony here. Close to 90 percent of Tibetans have a variant of EPAS1, while only 9 percent of Han Chinese in the region do. If China were to plan a Mars base, the minority Tibetans would have a genetic edge in recruitment over the majority population.
Pratik Kanjilal
