Why Birds Can Fly over Mount Everest

Bar-headed geese cross the Himalayas at extreme altitudes, where oxygen is scarce. Their ability to fly over Everest comes from birds’ highly efficient lungs: air flows in one direction through them, so oxygen-rich air keeps reaching the lungs during both inhalation and exhalation. Birds inherited this respiratory system from their dinosaur ancestors. The story asks why dinosaurs evolved such lungs, then traces a chain of consequences back hundreds of millions of years to plants colonizing land.

Land plants needed rigid support to grow tall, and lignin provided it by strengthening their cells. For a long time, fungi and bacteria could not break lignin down, so dead trees accumulated and buried carbon. The account links this carbon burial to a rise in atmospheric oxygen, which allowed insects and amphibians with less efficient respiratory systems to grow exceptionally large. As oxygen kept increasing, microorganisms faced the danger that the atmosphere could become flammable. Eventually, fungi evolved enzymes that dissolve lignin, enabling decay and returning oxygen to the cycle. The tale presents evolution as nature’s research and development: adaptations solve immediate problems but can create unforeseen effects. It connects plant evolution, fungal decay, changing atmospheric chemistry, dinosaur physiology, and birds’ high-altitude flight in one long sequence.