![]() These experiments reveal the existence of a gene called Sonic hedgehog, which controls the embryonic development of limbs in all limbed creatures. Shubin describes a number of biological experiments performed on chicken embryos. In Chapter 3, Shubin explores the similarities between human DNA and that of creatures as diverse as chickens, flies, and sharks. The following chapters of Your Inner Fish consider other parts of human anatomy, delving into each structure’s evolutionary history. Tiktaalik is the first known creature to evolve a limb, and thus shows how an “inner fish” is embedded within the human body (8). Though Tiktaalik is a fish, it contains the bone structure of an animal limb embedded within its fin. Chapter 2 shows how the ancient Tiktaalik provides information about human bodies-in particular, our limbs. Though the first expedition proves fruitless, Shubin finally discovers the fossil of Tiktaalik during a 2004 expedition. ![]() ![]() Hoping to find a fully preserved specimen, Shubin plans an expedition to an area of the Arctic likely to contain the desired fossil. Tiktaalik is significant because it provides insight into how ancient fish evolved to walk on land.Ĭhapter 1 takes place during the 1990s, when Shubin discovers the fossil of an ancient fish fin that appears to contain the structure of a shoulder bone. The first two chapters of Your Inner Fish describe one of Shubin’s most important scientific contributions: the discovery of the fossil Tiktaalik, an ancient fish that lived around 375 million years ago. ![]()
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