Choose the correct words for the blanks. Use this word bank and be careful with the spelling! Not all words will be used. Word bank: Homologous, DNA, evolution, fossils, proteins, similar, different, embryos, ancestor, offspring type your answer. is the theory that organisms gradually change over time. This theory has been thoroughly tested and there is enough conclusive data that evolution occurred in the past and continues to take place today. Several types of evidence support the theory of evolution including anatomy, early development, similarities in DNA, and the fossil record. type your answer. structures are body structures (ex. bone structures) that are type your answer. and shared by two or more organisms. These structures have helped us to classify vertebrate organisms including fish, amphibians, reptiles, birds, and mammals which all share a similar internal skeleton with a backbone. These structures help to show how certain species may have inherited a trait from a common type your answer. Similarities in embryological development can also provide evidence for evolution. Observing type your answer. of different species during various stages of early development can reveal similarities. Many different species share similar structures early on such as tails or gill slits, which demonstrates relationships and reveals common ancestors. The more structures they have in common, the more closely related the organisms. We can also compare the type your answer.. of organisms to note how many nitrogen base pairs (A-T; C-G) are the same. The more bases that match, the more similar two organisms are to one another. Because bases along a gene call for specific type your answer. to be created, scientists can compare the order of amino acids in a protein to see how similar species are. type your answer. provide "hard" evidence that organisms of today originated from a common ancestor and changed over time. Unfortunately, the evolutionary history of the earth and its fossil record is incomplete because many organisms don't leave behind fossils, creating gaps or "missing link." A missing link is a transitional fossil or species that exhibits traits common to both an ancestral group and its descendants. For example, the discovery of the Archaeopteryx bridged the gap between dinosaur and present day birds.