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William Aird: When Oxygen Becomes the Limiting Factor
May 20, 2026, 15:00

William Aird: When Oxygen Becomes the Limiting Factor

William Aird, Professor of Medicine at Harvard Medical School, shared a post on LinkedIn:

”When Oxygen Is Limiting

Humans exposed to hypoxia typically shift the oxygen dissociation curve to the right. But evolution repeatedly selected the opposite strategy in organisms adapted to chronically low-oxygen environments.

The bar-headed goose, which flies over the Himalayas, evolved a left-shifted hemoglobin with higher oxygen affinity.

Llamas adapted to altitude the same way. The human fetus also uses a left-shifted hemoglobin, allowing oxygen extraction within the relatively hypoxic placental environment.

And classic studies of humans with high-affinity hemoglobin variants suggest remarkable tolerance of hypoxia at altitude.

Acute physiology and long-term evolution may not solve oxygen limitation the same way. Perhaps short-term compensation and long-term optimization are not always aligned.

A reminder that cultural evolution can outpace natural evolution, including in medicine.”

William Aird: When Oxygen Becomes the Limiting Factor

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