Hemoglobin is well known as the molecule that transfers oxygen in blood, but its precursor, heme, is lesser known.
Finely tuned and exquisitely engineered, this system gave our ancestors enough oxygen not only to stay alive but to thrive in the face of grave challenges.
James Lovelock has pointed out that atmospheric levels of oxygen much above about 25 percent, let alone 30 percent, would cause raging conflagrations today.
Biologist Robert Waltzer briefly details the engineering wonder that permits oxygen to be carried by the blood.
How can Tibetans survive high altitudes that leave lowlanders gasping? The answer is found in broken genes.