Evolution must occur over many generations and a long time scale. Changes within the life of an individual do not constitute evolution. Thus, a tadpole becoming a frog is not evolution.

After the Industrial Revolution's smog polluted the trees and resulted in them darkening in color, it was much easier for the black moths to survive and reproduce, because the darkened trees provided them with better camouflage than the light-colored trees had. The white-colored moths, on the other hand, were now exposed to predation at a greater rate, because they were not camouflaged. Due to this change in the environment, the moth population became predominantly black-colored as it adapted. This is an example of natural selection in action.

The mechanism of evolution was described by Darwin as the "survival of the fittest." We need an answer that addresses the fact that the individuals best suited to survival pass on their genes more often than individuals that aren't as well-suited, and that over long periods of time, these changes an accumulate until new species arise. This means that the correct answer is "There are always differences in the genes of individuals of a species. Some differences give certain individuals a better chance of survival. In each generation, those individuals best-suited to survive the current conditions will have the highest success in passing on their genes. Over many generations, the accumulation of these changes leads to the creation of new species from existing species."

A selective pressure is a factor that promotes evolution by selecting for a trait that will allow better survival for the organism that is at risk for compromised survival. In the case of anoles, the presence of the brown anole has promoted an evolutionary change for the green anole. There is no evolutionary change that can be observed in the other instances. 

Evolution occurs over a given time and may be punctuated or stagnant.  As individuals are produced with different characteristics more fit for their environments, the population gradually changes.  Evolution may even cause speciation or the merging  of two species.  Evolution is the response of a changing environment and different species interactions- individuals do not evolve; rather, natural selection works in favor of those individuals who are more fit for the current environment.  Those more fit individuals will go on to produce more offspring with their same qualities, leading to a gradual change, or evolution, of a species, population, and community. 

Coevolution describes how two species that interact closely with each other for their survival can evolve in response to one another. Another example is lichens, which are fungi and bacterial cells that grow together to act as a single living organism. 

Sexual dimorphism is a phenotypic differentiation between males and females of the same species. These altered phenotypes occur in organisms that reproduce through sexual reproduction. Commonly referenced possible examples are body size, physical strength and morphology, ornamentation, behavior and other bodily traits. An example would be comparing bright green male peacocks to the brown and grey female peacocks. Genetic drift is a different, unrelated evolutionary concept. Evolutionary monomorphism and the sperm-egg model do not refer to real concepts.

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.

A vestigial trait is an attribute that has lost its function but has been retained through evolution. Examples include the formation of goose bumps in humans and pelvic remnants in boas and pythons. A change in the DNA sequence (genome) of a cell is a mutation. A trait that makes an organism better suited for a habitat is an adaption. Structures that arise in organisms that share a common ancestor, but perform different structures are called homologous structures. An example of a homologous structure is the "arm" of a mammal. Mammals have very similar bone and muscle organization in their arms (whales, humans, bats), but the function of each is much different (swimming, grabbing, flying).