In the book Your Inner Fish, by Neil Shubin, he introduces the concept of evolution and how we can trace the parts that make up the human body back to jellyfish, worms and even fish. The book explains not only how we became who we are today, but also the implications our ancestors had on our current body plan. In this essay I will demonstrate that I have digested Shubin's entire book by convincing you (dear reader) that everything in our body is based on simple changes to already existing systems. To make this point, I will use the evidence for limb development in a wide range of organisms, the four arches found in embryonic development, the structures inside our noses, and how our ears originated , all due to modifications. It's a plan common to all members: one bone, followed by two bones, then a bunch of small bones and finally numbers. This set of bones is seen in many species, including bats, whales and lizards. But how do these limbs develop and why do they all look the same? Shubin explains it by saying that there are certain genetic switches that help put together who we are. When scientists researched this genetic change in the limbs, they discovered a few areas of tissue in the limbs that allow this body plan to occur. “A band of tissue at the tip of the limb bud is essential for the development of any limb… This area of ​​tissue has been named the zone of polarizing activity (ZPA). » ZPA allows humans to have opposable thumbs and little fingers. In other organisms, it differentiates between the “thumb” side and the “little finger” side. Scientists then wanted to discover the molecule that allowed this change in ZPA, the answer is Sonic hedgehog. Shubin points out that every animal with limbs is in the middle of the paper. The rest of us is that we also share the Pax 2 gene which is active in the ear region and initiates a chain reaction of genetic activity leading to the development of the inner ear. This common gene shows evidence of a common history and shows how our bodies are made up of many modifications. Neil Shubin's book is very informative on how our inner fish is real and definitely present in our body today. I have given evidence to support how our bodies are based on (relatively) simple changes to already existing systems. This is still seen today when scientists study organisms with simpler body plans than ours to understand medical conditions and mutations in the human body. We were created through variations and modifications to become what we are today and that is an amazing thing. Our body plan was made possible by simpler organisms and this gave rise to the life we ​​know today..