Neil Shubin, the writer and narrator of Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body, is a paleontologist who researches early mammals, with a particular emphasis on how animals evolved to walk on land. Shubin’s work is focused on searching for undiscovered ancient animal species who might reveal how animals originally evolved limbs. However, finding such fossils is a difficult task, as “only a very small fraction [of ancient animals] are preserved as fossils” (8).

Though hunting for such fossils may seem like guesswork, paleontologists can pinpoint geographic locations likely to hold a desired type of fossil. By looking at the known fossil record, Shubin hypothesizes at what date in the earth’s history certain types of animals first developed. Shubin then consults geographic textbooks to discover areas where ancient rocks from this time period have been exposed to the earth’s surface through earthquakes or construction projects. Finally, Shubin searches for “sedimentary rocks: limestones, sandstones, silt-stones, and shales” (17), which are the most likely to contain preserved fossils.

Shubin’s research focuses on animals that existed between 380 and 365 million years ago, when ancient fish developed limbs and began walking on land as amphibians.