In Investigation Four, you learned that the genetic information of cells is translated into proteins by those cells. You also discovered that a mutation can alter the function of a protein. This can result in a change in the function of a trait found in a specific organism.

Each species consists of individual organisms that appear more similar to one another than to the individuals of another, different species. The fact that each species consists of individual organisms that are slightly different from one another is a consequence of the normal biologic variation within a species. For example, the species Homo sapiens (modern species of humans) includes a wide variety of individuals who are different in appearance from each other but are nearly identical to each other than to individuals of other primate species. A similar physical appearance, or phenotype, is due to the contribution of many different traits, all of which are similar but not identical for a species. All of these traits are controlled by genetic information contained in cells.

The genotype (genetic profile) of an individual or a species is the combination of the different genes that determine an individual or species’ phenotype (observable traits) since the genotype determines the phenotype. In the simplest case, each trait is determined by one of two different alleles of a single gene, one dominant allele, and one recessive allele.

In reality, most traits are so complex that each trait is determined by a combination of alleles of many different genes. Since the phenotypes within a species are slightly different, it is reasonable to assume that the genotype of a species is slightly different from individual to individual. These slight differences in both phenotype and genotype are a result of genetic variation. Sexual reproduction, with its recombination of genetic information, ensures the continuation of variation since each allele is paired with a different allele during sexual reproduction.

The environment of a species includes factors such as weather, temperature, food supply, water supply, and other organisms. All of these factors have a direct effect on the well-being of a species. Changes in one factor of a species’ environment over either a short or long time interval affect whether a species will effectively survive and reproduce. Adaptation of the species occurs via an increase in the proportion of the individuals that possess a trait that permits survival. Adaptation to environmental pressure is necessary if the species as a whole is to survive. If the species cannot survive an environmental change, all individuals will eventually perish and the species will become extinct.

Each individual within a species is slightly different because the traits of each individual are slightly different. When an environmental factor changes and environmental selection pressure is exerted, one of these slightly different traits may offer a survival advantage to the individuals that possess the trait. As these individuals reproduce, the trait is passed to the individuals’ offspring providing a survival advantage to new individuals. Those individuals without the advantageous trait do not survive but those with the trait survive and reproduce until all individuals of the species possess the particular gene and exhibit the advantageous trait. What was once genetic variation is now a gene common to all individuals of the species. Individual organisms do not adapt; the environmental pressure on the individuals of a species results in adaptation of the species as a whole, a process that is termed natural selection. The British biologist and geologist Charles Darwin was instrumental in discovering how natural selection, when applied over long periods of time, can cause species to change forms and evolve.

In this Investigation, you will use a model to test the effect of natural selection on a population of beetles. In this model, camouflage will be the advantageous trait. The better-camouflaged beetles will have a higher survival rate than beetles that are not well camouflaged. However, camouflage depends on the color of the environment as well as the color of the beetles. You will examine this population of beetles over a three-year time period and evaluate the traits which are passed to the beetles’ offspring.