Common descent has proven to be the most parsimonious way to explain the connections that have been and still are found between seemingly unrelated organisms. In this essay I will demonstrate that I have digested Shubin's entire book by convincing you that there is a lineage that connects all vertebrates. To illustrate this case, I will describe several connections observed in fossils and in the genes of different animals. Many of these connections involve a common pattern, modifications of which are found in all vertebrate species. These designs observed in both primitive and modern vertebrates serve as excellent evidence of descent from a common ancestor. Shubin described Sir Richard Owen's discovery of an underlying design in the arrangement of limb bones in land animals, which he refers to as an Owen two-bone. model of bones-many blob figures. In humans, for example, the humerus always articulates with the ulna and radius, followed by the carpals which connect with the fingers. The difference in this design between species is visible in the size and shape of the bones. This recurring pattern in vertebrate land animals can be explained by descent from a common ancestor who had the limb bones arranged in the same way. It therefore follows that there should be a fossil of this common ancestor indicating the transition between finned fish and limbed amphibians. Not unexpectedly, Tiktaalik, a perfect intermediate was found in a rock of suitable age. It has a flattened head and neck seen in land animals and the one-bone, two-bone, and many shapeless digit pattern in its fins. It also has scales and webbed fins, characteristic of fish. By examining fossils and extant organisms such as zebrafish, lungfish,...... middle of paper...... quality is easily explained by descent from a common ancestor. In conclusion, I know it is safe to say the list of evidence Shubin provides for common descent continues. They range from similar patterns in the embryonic development of ears, to the way different vertebrates produce odors. Fossils and genes individually provide a good deal of evidence of an unbroken evolutionary line, but together the evidence has greater significance. You might wonder why it is so important to prove descent from a common ancestor. For some, it might just be to satisfy curious human nature, but for others, it's much more. For example, practitioners of modern medicine will benefit immensely from understanding this history. In any case, the evidence is there, but everyone is free to choose what to do with it and how it influences (or does not influence) their beliefs..