EVIDENCE OF EVOLUTION There are four types of evidence that we use to remember how evolution has occurred: fossil evidence, comparative embryology, comparative anatomy, and molecular evidence.
FOSSIL EVIDENCE This refers to the fossils- ancient remains from the past- that have been kept preserved and stored over time. Most of the evidence from evolution actually comes from fossil records and discoveries. However, the fossil record often has gaps and do not show where the intermediate fossils or changes occurred. Often, these fossils display similar, or homologous, structures to the modern species that exist today. One example would be a modern alligator like the one shown below compared to older fossils. The fossils preserved from earlier years look similar to the common alligator species that we see today, much like other specimen.
COMPARATIVE ANATOMY There are two types of comparative anatomy: homologous structures, and analogous structures. Comparative anatomy itself describes the comparison of similar bone or organ structures of ancient organisms to modern species. When comparing homologous structures, we look for similar bone or organ structure. This displays that they have a common ancestor. However, the organisms have homologous structure, but do not have the same DNA or genes. One of the examples, shown to the left below, is the comparison between a human, lizard, cat, whale, bat, frog, and bird. When we look at the bone structure between the seven different species, we can see they have the same arm and hand bone structure. Analogous structures, unlike homologous structures, are not helpful and are not a good example of evidence. They describe organisms having the same job, but do not have similar structures, so they do not have the same genes. As shown below on the right, we can compare the structures of four different species. We can see they have similar wings- they are used for the same thing- but have different structures of wings.
COMPARATIVE EMBRYOLOGY This type of evidence describes how the first stages of a growing organism, known as an embryo, often relate to the embryos of another organism. The embryos usually experience very basic genes at the start, which makes it very easy to see the common ancestors between organisms. For example, as shown below, we can see the common similarities between a fish, salamander, tortoise, chick, pig, calf, rabbit, and human. Without the labels, it would be difficult to tell the difference between the embryos in their early stages. This displays the organism had or once had a common ancestor.
MOLECULAR EVIDENCE There are two types of molecular evidence that we look at in order to compare and contrast organisms. Studying molecular evidence describes the examination of an organism's genes or its proteins, which is very lab- intensive, but usually shows the majority of evidence for common ancestors and evolutionary relationships. The first type is amino acid sequences, which display that related mutations can happen within any population at the exact same rate. However, the difference of the populations will increase the longer the two separate populations are kept apart and isolated. These differences are known as a "molecular clock", which can estimate how long the two gene pools of the populations have been separated. As shown below on the left, we can see through a molecular clock that the difference between species A and species B is smaller than the difference between species B and species C. This displays that species A and species B were not distanced for as long as species B and species C were from each other. The second type is the comparison of DNA. This describes when several individuals of the same species have DNA that look similar. However, there are also a lot of chances for interbreeding species to spread mutations, which can very quickly reproduce and change in the gene pool. Isolated species can also create mutations, but they collect their own, and these mutations soon become vulnerable to environmental pressures. Over time, speciation will occur and a new species will be created, which will have identical DNA to the previous species. As shown below on the right, we can see the DNA sequences between a human, chimpanzee, and gorilla are almost identical, while the orangutan differs from the others. This displays that the human, chimpanzee, and gorilla once had or have a common ancestor.