Your Inner Fish: Chapter 1 Summary & Analysis

Preface. Neil Shubin describes how he taught a human anatomy course at the University of Chicago, though his degree was in paleontology and his specialty was fish. Yet Shubin’s knowledge of other animals gave him the opportunity to explain complex human anatomy in terms of simpler animal anatomy. The second year he taught the course, Shubin found a fossil fish from the period of transition between water animals and land animals, and this discovery reframed how he thought about the human body.

Shubin has now spent many summers in the Arctic looking for fossil fish. Fossils are the only way to see what life was like on Earth in the distant past, and therefore are a key part of understanding how life developed into human life. These fish give fundamental clues to understanding the human body.

Digging Fossils – Seeing Ourselves. On Ellesmere Island, with a latitude of 80 degrees north, Shubin finds a fossil fish with a flat head. He is in the Arctic because the Arctic region is one of the best places to reliably find fossils. With new technology that allows paleontologists to scan potential field sites before digging, fossils are in some ways easier to find than they once were. But fossils are so fragile that digging them out by hand is still laborious, time-consuming work – often in harsh terrain and weather conditions.

Fossil sites depend on three things: rocks of the right age, rock types that can preserve fossils, and rocks that are exposed on the surface. To look for fossils from the transition between water animals to land animals, Shubin has to find rocks that are older than 365 million years old. Luckily, the arrangement of rock layers on Earth leaves a relatively stable timeline with the oldest rocks on the bottom and more recent rocks on top. Earthquakes and fault shifts can disturb this pattern, but there is usually enough evidence to put the timeline back together.

Fossils inside the rock layers also follow the progression of oldest on bottom to youngest on top, starting with jellyfish-type creatures, moving through various animals with skeletons, all the way to humans. Looking at a zoo from today can actually help paleontologists predict what type of animal will be in each age of rock layer. They do this by focusing on the traits that animals share.

Everything in the zoo has a head and two eyes. A subset adds limbs. The next subset adds another feature. The more unique a subset is, the younger it is. Thus Shubin expects to find fossils with a head and two eyes in rock layers below fossils with a head, two eyes, and limbs. By analyzing thousands of animal characteristics and species, paleontologists have formed a catalogue of what age rock holds which type of fossils.

For the first fossils with limbs, the rock layer comes from the critical time period from 380 million years ago to 365 million years ago. 360-million-years-old rocks already show diverse life forms that look like modern day amphibians (frogs and salamanders). Shubin decided to focus on 375-million-years-old rocks to maximize his chances of finding fossils of the first creatures with limbs.

The best type of rock for finding fossils is sedimentary rock, as volcanic and metamorphic rocks form in conditions too violent to allow fragile fossils to stay intact. Sedimentary rocks all over the world show that the geography and climate of Earth has changed significantly over time, with oceans or tropical rainforests where there are now mountains and deserts.

The last step for choosing a fossil site is finding a layer of sedimentary rocks of the right age that is not covered by human settlements. These three factors are almost always easier to find in deserts. However, it is very expensive to mount a full fossil-finding expedition to a desert like the Gobi or the Arctic.

Shubin starts his fossil-finding expedition researching the origin of limbs in his hometown of Philadelphia. The Catskill Formation of Pennsylvania actually holds rocks from the Late Devonian Period that contain valuable fish specimens. Shubin and one of his students, Ted Daeschler, check sites of exposed rock recently blasted by the Pennsylvania Department of Transportation to make new roads. They are rewarded with a shoulder bone from a hynerpeton, a small amphibian.

With one new fossil found, Shubin and Daeschler are ready for more. Looking at a geology textbook, they notice that rocks from the Devonian Period are also in the Alaskan Yukon (which has already been well-studied), the coast of Greenland (where Jenny Clack found an early creature with limbs), and the Canadian Arctic—which has rocks almost identical to the rocks in Pennsylvania. Shubin and Daeschler decide to go to Canada because it has not yet been explored by vertebrate paleontologists.

An expedition to the Arctic comes with many dangers, including the local wildlife, unpredictable weather, and the limited ability to carry supplies when the team is airlifted to dig sites. Furthermore, Shubin and his team can only go to the Arctic during the summer. Shubin brings in Dr. Farish Jenkins, his graduate advisor from Harvard, who has years of experience leading expeditions in similar conditions in Greenland.

Shubin spends the first few weeks at the dig site worrying about polar bears. The Arctic landscape is vast and empty, making the search for fossils less than four feet long even more improbable. In 1999, Shubin and his team find plenty of fish fossils from deep water, but none of the shallow-water fish they need to start looking for the transition to land-living animals.

In 2000, Shubin and his team move their dig site east to Ellesmere Island. There, a college undergraduate named Jason Downs is late returning to camp one night. Just as the senior members of the team are ready to mount a search party for Downs, Downs returns to camp with his pockets full of fossil fragments. The whole team heads out to the river bed where Downs identified these fossils, and they spend several days identifying the exact rock layer that might hide intact fossil fish skeletons. They eventually find intact skeletons, but the fish are all of species that have already been documented.

In 2004, Shubin and his team make one last expensive trip to the Arctic. Finally, Shubin finds a fish fossil fragment with a jaw that suggests the fish had a flat head. Then another team member, Steve Gatesy, finds a full fish skeleton with the same flat jaw. Over the next two months, fossil preparators meticulously expose this fossil from the rock, discovering that it is an intermediate between fish and land animals. This fish fossil has scales like a true fish, but a neck, flat head, and small limbs like a land animal.

This fish find is a huge success for the idea that there is a transitional stage between fish and amphibians at the 375-million-year time period. Shubin, Daeschler, and Jenkins decide to thank the Inuit people for allowing them to work in the Nunavut territory by giving the fish fossil a name that reflects the Inuit heritage. The Inuit Committee of head elders suggests Siksagiaq or Tiktaalik. Shubin decides on Tiktaalik, which means large freshwater fish.

Tiktaalik’s discovery is a huge news story in 2006, but Shubin is most affected by a moment in his son’s preschool class. Shubin takes the Tiktaalik fossil to his son Nathaniel’s show-and-tell. When one child asks if the fossil is a fish or a crocodile, another child responds that it can be both. More than bridging the gap between fish and reptiles, Tiktaalik offers insight into all the body structures that land animals share.

Tiktaalik shows human’s history as fish the same way that the famous “Lucy” (an early human ancestor discovered in Ethiopia) shows human’s history as highly advanced primates. Human anatomy is the result of millennia of small shifts in the bone structure of all animals. These shifts can be seen in the fossil record, as well as in genes and DNA.