Breath of Fresh Air

When Napoleon Bonaparte invaded Egypt in 1798, he brought more than ships, soldiers, and weapons with his army. Seeing himself as a scientist, he wanted to transform Egypt by helping it control the Nile, improve its standard of living, and under­stand its cultural and natural history. His team included some of France's leading engineers and scientists. Among them was Étienne Geoffroy Saint-Hilaire (1772–1844).

Saint-Hilaire, at twenty-six, was a scientific prodigy. Already chair of zoology at the Museum of Natural History in Paris, he was destined to become one of the greatest anatomists of all time. Even in his twenties, he distinguished himself with his ana­tomical descriptions of mammals and fish. In Napoleon's retinue he had the exhilarating task of dissecting, analyzing, and nam­ing many of the species Napoleon's teams were finding in the wadis, oases, and rivers of Egypt. One of them was a fish that the head of the Paris museum later said justified Napoleon's entire Egyptian excursion. Of course, Jean-François Champol­lion, who deciphered Egyptian hieroglyphics using the Rosetta Stone, likely took exception to that description.

With its scales, fins, and tail, the creature looked like a standard fish on the outside. Anatomical descriptions in Saint-Hilaire's day entailed intricate dissections, frequently with a team of art­ists on hand to capture every important detail in beautiful, often colored lithographs. The top of the skull had two holes in the rear, close to the shoulder. That was strange enough, but the real surprise was in the esophagus. Normally, tracing the esophagus in a fish dissection is a pretty unremarkable affair, as it is a simple tube that leads from the mouth to the stomach. But this one was different. It had an air sac on either side.

This kind of sac was known to science at the time. Swim bladders had been described in a number of different fish; even Goethe, the German poet and philosopher, once remarked on them. Present in both oceanic and freshwater species, these sacs fill with air and then deflate, offering neutral buoyancy as a fish navigates different depths of water. Like a submarine that expels air following the call to "dive, dive, dive," the swim bladder's air concentration changes, helping the animal move about at vary­ing depths and water pressures.

More dissection revealed the real surprise: these air sacs were connected to the esophagus via a small duct. That little duct, a tiny connection from the air sac to the esophagus, had a large impact on Saint-Hilaire's thinking.

Watching these fish in the wild only confirmed what Saint-Hilaire inferred from their anatomy. They gulped air, pulling it in through the holes in the back of their heads. They even exhib­ited a form of synchronized air sucking, with large cohorts of them snorting in unison. Groups of these snuffling fish, known as bichirs, would often make other sounds, such as thumps or moans, with the swallowed air, presumably to find mates.

The fish did something else unexpected. They breathed air. The sacs were filled with blood vessels, showing that the fish were using this system to get oxygen into their bloodstreams. And, more important, they breathed through the holes at the top of their heads, filling the sacs with air while their bodies remained in the water.

Here was a fish that had both gills and an organ that allowed it to breathe air. Needless to say, this fish became a cause célèbre.

A few decades after the Egyptian discovery, an Austrian team was sent on an expedition to explore the Amazon in celebra­tion of the marriage of an Austrian princess. The team collected insects, frogs, and plants: new species to name in honor of the royal family. Among the discoveries was a new fish that, like any fish, had both gills and fins. But inside it also had unmistakable vascular plumbing: not a simple air sac, but an organ loaded with the lobes, blood supply, and tissues characteristic of true human-like lungs. Here was a creature that bridged two great forms of life: fish and amphibians. To capture the confusion, the explorers gave it the name Lepidosiren paradoxa—Latin for "paradoxically scaled salamander."

Excerpted from Some Assembly Required by Neil Shubin. Copyright © 2020 by Neil Shubin. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.