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1-Page Summary of Your Inner Fish

Overall Summary

In his book, Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body, author Neil Shubin explores how humans evolved from other animals on Earth. As he does this, he shows how closely related we are to all living things on Earth and why they’re so important to us today.

The first two chapters of Your Inner Fish describe one of Shubin’s most important scientific contributions: the discovery of Tiktaalik, an ancient fish that lived around 375 million years ago. Tiktaalik is significant because it provides insight into how ancient fish evolved to walk on land. During his 1990s expedition in search of fossils, Shubin discovered a fossil fin that contained the structure of a shoulder bone. Hoping to find more evidence, he planned another Arctic expedition for 2004 and finally found Tiktaalik during this trip. The ancient Tiktaalik shows how humans evolved from fish—humans have limbs like those embedded in fins.

The author then explores the inner workings of other parts of our anatomy, such as DNA. He delves into how similar it is to creatures as diverse as chickens, flies and sharks. The author describes a number of experiments performed on chicken embryos that reveal the existence of a gene called Sonic hedgehog which controls limb development in all limbed creatures.

In the fourth chapter, Shubin talks about how fossil records show that mammalian teeth have existed for millions of years. However, mammals developed a unique jaw structure suited for consuming diverse diets when they evolved. In the fifth chapter, Shubin explains that human skulls appear to be internally complex but are actually governed by a precise pattern shared with all living things on earth.

In Chapter 6, Shubin describes a number of biological experiments performed on salamander and fly embryos. These experiments reveal the existence of the Organizer, a small patch of tissue that tells the embryo how to build a body structure. In Chapter 7, Shubin discusses how creatures with bodies first evolved millions of years ago. Experiments on living single-celled organisms called choanoflagellates reveal that these organisms contain all of the molecular tools necessary to form a multi-cellular body.

Chapter 8 focuses on the evolutionary history of our sense organs. It explains how we were able to smell with a single gene that corresponds to each odor we can detect. Chapter 9 reveals how eyesight is made possible by a molecule called opsin, which exists in the eyes of every creature, regardless of eye structure. Chapter 10 talks about ears and how mammals evolved their middle ear bones from jaw bones of fish and reptiles so they could hear higher-frequency sounds.

In Chapter 11, Shubin discusses why it’s important to understand the evolutionary history of our body parts. He mentions how many illnesses arise due to the “inner fish” inside us. For example, human hiccups occur because we have a vestigial tadpole breathing system that looks like a tail. In addition, hernias happen because sharks have their gonads in an unusual location which influences the structure of the human scrotum and leads to hernias. Shubin also explains mitochondria, bacteria from another species that live within our cells today.

Chapter 1: “Finding Your Inner Fish”

Neil Shubin is a paleontologist who studies early mammals. He has a particular interest in how animals evolved to walk on land, but it’s difficult to find fossils of ancient animals. Only a very small fraction are preserved as fossils.

Paleontologists can find fossils by looking at the known fossil record and figuring out when certain types of animals first existed. They then look up information about where those rocks are located, such as in textbooks that show earthquakes or construction projects exposed them to the surface. Then they search for sedimentary rocks, which are most likely to contain fossils.