Darwin's finches were distinct from one another due to the size and shape of their beaks. Darwin noted that these distinct beaks allowed the different birds to eat specific food groups. The varying food groups allowed the animals to coexist in the same habitat, without resorting to competing for natural food resources. Each species had evolved to occupy a unique ecological niche in order to survive with minimal competition for resources.

Evolution is a theory that accounts for the changing and transformation of organisms throughout history. For evolution to take place, mutations must occur and change the genetic identity of a population. Essentially, evolution is evidenced by changes in genetic diversity and allele frequency. Each of the answer choices contributes towards the theory of evolution.

Natural selection was coined by Darwin, whose work helped with the theory, and describes the tendency for traits that aid in survival to become more prevalent in a population. Vestigial structures are organs in modern organisms that serve no purpose in increasing biological fitness, but may have been useful to ancestral species in history. Common ancestor organisms are different species that share genetic information with modern species, suggesting that genetic changes in the historic species may have produced the modern species. The fossil record provides genetic material and physical evidence of historic species to use for comparison with modern organisms.

The correct answer is that mitochondrial DNA is found in the mitochondria, where it takes the form of a plasmid, or ring-shaped structure characteristic of bacterial DNA. (This provides evidence in favor of the endosymbiotic theory.) Furthermore, in humans and in many other organisms, mitochondrial DNA is passed down solely through the maternal line. Note that the answer choice "It is found in a plasmid in the nucleus" is inherently non-sensical; plasmids are characteristic of prokaryotes, which do not have nuclei, as they do not have membrane-bound organelles.

Homologies are physical similarities resulting form common ancestry. This is the reason that related species share similar features. Therefore, homologous structures are anatomical similarities in organisms due to a shared ancestry. On the other hand, analogous structures are the result of convergent evolution. Convergent evolution is defined as the evolution of similar anatomical features in independent evolutionary lineages. In response to a changing environment, natural selection favored animals with similar traits or features that evolved independently as a result of adaptation to environmental alterations.

When a mutation in a gene prevents it from being read, it may be advantageous if the compound produced by the encoded enzyme can be readily obtained from outside sources, saving energy needed to produce the compound on one's own.

A well-known example of this is the GLO gene for vitamin C production. In fruit-eating animals like bats, guinea pigs, and humans, the gene is still present but has a broken promoter, rendering it nonfunctional.

Homologous structures show the existence of a shared ancestry through the observation of structural similarities between different species; however, while a human's hand and a cat's paw are structurally similar, they have very different functions.

Structures that are similar as a result of convergent evolution are referred to as analogous structures, such as the wings of beetles and birds. These animals do not share a common ancestor, and developed the trait for wings independent of one another. Homologous structures arise when two organisms share a trait due to linkage with a common ancestor. For example, legs of a dog and the legs of a cat are considered homologous.

Phylogeny refers to the evolutionary history of a lineage, and can be used to identify common ancestors. Taxonomy is the naming and classification of organisms. Binomial nomenclature is the scientific name for an organism containing its genus and species.

Analogous structures are anatomical structures that have similar functions, but arose independently. Due to environmental stresses and natural selection, organisms of different species evolved and adapted independently, resulting in the existence of body parts with similar functions. This refers to convergent evolution. An example of analogous structures are the wings of several different animals. A moth, hummingbird, and a bat are only extremely distantly evolutionarily related, yet they all have wings of some sort, which serve the common purpose of transportation through air. Homologous structures are body parts that are anatomically similar and may share similar anatomical forms, but are not the result of convergent evolution, rather they are the result of divergent evolution. These commonalities within organisms show descent from a common ancestor. An example of homologous structures are the "arms" of three different mammals, a human, a bat, and a whale. Each "arm" has very similar anatomical organization of bones, but is used for very different functions.

Before any truly accurate scientific work on evolution and inheritance could be done, the academic community had to accept the notion that the Earth and its species change over time. If species were fixed, then genetic variation, natural selection, and evolution could not be plausible. Once the scientific community acknowledged the changes in organisms, they were able to proceed into studies to determine why and how such changes occur.

By definition, vestigial structures are structures that are thought to have had a biological function a long time ago but have since lost that function due to evolutionary changes. The human appendix is considered to be an example of a vestigial structure.