-Comparative Anatomy Provides Structural Evidence of Evolution
Appearance has long been used as an indicator of the relatedness of organisms. Structure, inexorably tied to function, also provides evidence of descent with modification. The elephant and the mammoth, for instance, clearly have similar anatomies and share a common ancestor.
Unrelated Species in Similar Environments Have Evolved Similar Forms
Evolution by natural selection also predicts that, given similar environmental demands, unrelated species might independently evolve superficially similar structures, a process called convergent evolution. Such outwardly similar body parts in unrelated organisms, termed analogous structures, may be very different in internal anatomy, because the parts are not derived from common ancestral structures. The wings of flies and of birds are analogous structures that have arisen by convergent evolution; the fat-insulated, streamlined shapes of seals (mammals) and of penguins (birds) .
Homologous and Vestigial Structures Provide Evidence of Relatedness of Organism Adapted to Different Environments
Modern organisms are adapted to a wide variety of habitats and lifestyles. The forelimbs of birds and mammals, for example, are variously used for flying, swimming, running over several types of terrain, and grasping objects such as branches and tools. Despite this enormous diversity of function, the internal anatomy of all bird and mammal forelimbs is remarkably similar. It is inconceivable that nearly the same bone arrangement could be ideal for different functions, as we would expect if each animal had been created separately. Such similarity is exactly what we would expect, however, if bird and mammal forelimbs were derived from a common ancestor. Through natural selection, each has been modified to perform a particular function. Such internally similar structures are called homologous structures, meaning that they have the same evolutionary origin despite possible differences in function. Studies of comparative anatomy have long been used to determine relationships among organisms, on the grounds that the more similar the internal structures of two species, the more closely related the species must be; that is, the more recently they must have diverged from a common ancestor.
-Biogeography is an active field, exploring how geographic distribution of life is affected by history, climate, geology, and behavior. As predicted by evolution, the geographical arrangements of related species repeats in different groups. This comparison of multiple lineages shows how the shared history of an area produces similar patterns of common ancestry, and allows us to test hypotheses about evolution. The rapid ecological and morphological diversification of organisms on islands shows how quickly evolution can produce novelty. -The DNA in living things is highly conserved. DNA has only four nitrogenous bases that code for all differences in living things on Earth. Adenine, Cytosine, Guanine, and Thymine line up in a specific order and a group of three, or a codon, code for one of 20 amino acids found on Earth. The order of those amino acids determines what protein is made.
Remarkably enough, only four nitrogenous bases that make only 20 amino acids account for all diversity of life on Earth. There has not been any other code or system found in any living, or once living, organism on Earth. Organisms from bacteria to humans to dinosaurs all have the same DNA system as a genetic code. This may point to evidence that all life evolved from a single common ancestor.
The more closely species are related on the phylogenetic tree of life, the more closely their DNA sequences will overlap. Even very distantly related species will have some degree of DNA sequence overlap. Certain proteins are needed for even the most basic processes of life, so those selected parts of the sequence that codes for those proteins will be conserved in