Editor’s Foreword

The Blood That Never Thickened

On Professor Girma Berhanu’s review of the genetic architecture of high-altitude adaptation in Ethiopia — what the highland body records, and what it cannot be made to say.

At three thousand metres above the sea, the air is still one-fifth oxygen. The proportion never changes; the pressure does. Every breath drawn on the Simien escarpment delivers fewer molecules to the blood than the same breath drawn on the Red Sea littoral, and the body must make up the difference or fail. Most bodies, arriving suddenly, make it up badly. The marrow floods the circulation with red cells, the blood thickens, the heart labours, and the newcomer acquires — sometimes permanently — the cluster of afflictions that mountain medicine calls chronic mountain sickness.

The farmer walking to market above Debark does not acquire it. His haemoglobin is, by the standards of the physiology textbooks, unremarkable. His arterial oxygen saturation is likewise unremarkable. By every measure that ought to declare him a highlander he reads as a man at sea level — and yet he is not at sea level, and he is not ill. That is the puzzle Professor Girma Berhanu’s review sets out to survey, and the answer the literature supplies is that the peoples of the Ethiopian highlands appear to have solved the problem of thin air by a route no other high-altitude population took.

There are, on current evidence, three great natural experiments in human hypoxic adaptation: the Andes, the Tibetan plateau, and the Ethiopian highlands. Andean populations carry elevated haemoglobin. Tibetans carry comparatively low haemoglobin with reduced saturation and a well-characterised genomic signal. Ethiopians, as Cynthia Beall and her colleagues reported in 2002, display neither compensation and no evident cost — a third solution, arrived at independently. The genomics followed a decade later, when two 2012 studies identified candidate loci among Amhara highlanders that are largely distinct from the Tibetan signal while sitting, in part, within the same oxygen-sensing pathway. This is convergent evolution in its textbook form: separate roads to the same summit.

It is worth noticing how late this arrived. The Andes and Tibet have been studied for the better part of a century; Ethiopia entered the genomic literature only in the past fifteen years. That lateness is not a fact about Ethiopian bodies. It is a fact about where laboratories are built and whose questions get funded, and it is the reason this Tribune takes an interest in a review that might otherwise belong solely to the journals.

Professor Berhanu does not conceal the argument that moved him to write, and we would not permit him to. He is answering a claim now in wide circulation: that the Amhara are not a people but a residue — a miscellany of origins fused by an administrative language, invented late and by decree. He finds this claim in uneasy company with itself. The same discourse that declares the Amhara never to have existed as a community identifies them with great precision when they are counted among the dead.

The Tribune publishes this review, and publishes it with a stated boundary. Professor Berhanu draws that boundary himself, in his own third paragraph, and it is the most important sentence in the manuscript: genetics can illuminate ancestry and continuity, but cannot by itself determine when an ethnic identity came into being. Long habitation of the highlands is a question of evidence, and the evidence is strong. The formation of a self-conscious Amhara community is a question of history, and history is where it must be argued. A reader who comes to these pages hoping to find a biological warrant for a political claim will not find one. The author has taken some care that he should not.

The same caution applies, doubled, to the review’s passages on the brain. Professor Berhanu engages the literature that once proposed cold climates as engines of intelligence and dismisses it as methodologically and conceptually unsound, which is the settled view and the correct one. He then asks the open question — whether long ecological demand shapes cognition at all — and answers that the evidence is insufficient. We would put it more flatly. Nothing in this literature licenses the ranking of Ethiopia’s peoples against one another, and any reader who extracts such a ranking from it has misread it deliberately.

One figure deserves to be carried out of the manuscript and held up on its own. When researchers compared Amhara and Oromo highlanders in 2012, the genome-wide divergence between the two populations measured 0.0098 — a number so small it means, in plain terms, that they are very nearly the same people. Their physiological differences are real and appear to track how long each community has lived in thin air, not how far apart they stand. In a country where difference is the working currency of politics, that decimal is the most eloquent line in the paper.

The highland body keeps a record older than any chronicle, written in vessels rather than in Ge’ez. It says only that people were here, for a very long time, and that they endured. That is not a small thing to know. It is also not a licence for anything at all.

— The Editor, The Ethiopian Tribune

Synopsis

The Genetic Architecture of Adaptations to High Altitude in Ethiopia: The Amhara People as a Case Study. Girma Berhanu, Professor, Department of Education and Special Education, University of Gothenburg. A review of the literature.

Point of Departure

The review opens by separating two propositions frequently conflated in Ethiopian debate: the antiquity of human occupation in the highlands, which the archaeological, genetic and physiological record supports strongly, and the historical emergence of Amhara ethnic identity, which the author holds to be a question for historians and linguists rather than geneticists. He states the political provocation openly — the contention that the Amhara are a recent linguistic assemblage rather than an indigenous community — and answers it with the documentary record of highland settlement while conceding that admixture, migration and intermarriage are universal and diminish nothing.

The Physiology of Thin Air

Falling atmospheric pressure, not falling oxygen concentration, produces chronic hypoxia at altitude. Populations resident for many generations show adaptations in chest morphology, lung volume, vascular regulation and metabolism — but not identical ones. Elevated haemoglobin, long treated as the signature of successful adaptation, carries costs in blood viscosity and cardiovascular strain. Ethiopian highlanders, the review argues, largely avoid that trade-off.

The Ethiopian Pattern

Drawing on Beall and colleagues (2002), Cheong and colleagues (2017) and Getu (2022), the review sets out the distinctive Ethiopian profile: normal haemoglobin concentration with maintained arterial oxygen saturation and no chronic mountain sickness. The proposed mechanism is vascular rather than haematological, involving nitric oxide and cyclic GMP signalling that improves vasodilation and tissue oxygen delivery without recourse to excess red cell production. Notably, the pattern is not uniform within Ethiopia: Oromo highlanders from Bale have shown greater erythropoietic response than Amhara populations of the Simien.

The Genomic Evidence

Genome-wide work by Scheinfeldt and colleagues (2012) identified candidate loci — CBARA1, VAV3, ARNT2 and THRB — associated with hypoxic adaptation among Amhara highlanders, largely distinct from Tibetan and Andean signals though partly convergent within the hypoxia-inducible factor pathway. Alkorta-Aranburu and colleagues (2012) compared Amhara and Oromo participants born and raised at comparable elevations and found divergent adaptive phenotypes against negligible genome-wide differentiation (mean F_ST = 0.0098), proposing duration and intensity of highland residence rather than separate evolutionary histories as the likelier explanation.

Brain, Cognition and the Limits of Inference

The review surveys neuroimaging findings on chronic hypoxia — structural change in the insula, anterior cingulate, prefrontal and motor cortices — and stresses that outcomes depend on exposure duration, developmental history, nutrition, health and degree of adaptation. It examines and rejects the racial-IQ tradition on methodological and empirical grounds, treats the animal literature on high-elevation problem-solving as suggestive but not transferable, and concludes that no present evidence establishes permanent cognitive differences between human populations attributable to altitude.

Conclusion

Ethiopia’s highlands constitute one of the world’s most significant and least studied laboratories of human adaptation. Multiple pathways to hypoxic tolerance exist among neighbouring and closely related populations, which the author reads as an argument against hierarchy rather than for it. Existing work concentrates on Bale, Arsi, Welega, Shewa and the northern highlands; its findings cannot be extended to Afar, Somali or other lowland communities, and the author calls for research spanning Ethiopia’s full ecological range.

Professor Berhanu’s full review, with complete citations and the discussion in his own words, follows below: Read the full article ↓the-genetic-architecture-of-adaptations-to-high-altitude-in-ethiopia.docx