Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body

by Neil Shubin

In the mid-1800s, anatomists began to learn of mysterious living fish from the southern continents. One of the first was discovered by German anatomists working in South America. It looked like a normal fish, with fins and scales, but behind its throat were large vascular sacs: lungs. Yet the creature had scales and fins. So confused were the discoverers that they named the creature Lepidosiren paradoxa, “paradoxically scaled amphibian.” Other fish with lungs, aptly named lungfish, were soon found in Africa and Australia. African explorers brought one to Owen. Scientists such as Thomas Huxley and the anatomist Carl Gegenbaur found lungfish to be essentially a cross between an amphibian and a fish. Locals found them delicious. A seemingly trivial pattern in the fins of these fish had a profound impact on science. The fins of lungfish have at their base a single bone that attaches to the shoulder. To anatomists, the comparison was obvious. Our upper arm has a single bone, and that single bone, the humerus, attaches to our shoulder. In the lungfish, we have a fish with a humerus. And, curiously, it is not just any fish; it is a fish that also has lungs. Coincidence?