Development of genetically modified organisms is an example of artificial selection due to human intervention. Desirable organisms are allowed to generate offspring, passing on the selected genes. Non-optimal organisms are prevented from creating offspring.

The other options are all evolutionary changes that occurred naturally. Snake coloration is a mechanism to avoid predators and stalk prey. A giraffe's neck facilitates accessibility to its food source. An insect that is resistant to a certain chemical will survive to create offspring.

As an example of decent with modification, Darwin observed different species of finches on the Galapagos Islands and thought that they had descended from a common ancestor. Individuals that have inherited advantageous traits are likely to produce more offspring than other members of the population, which drives natural selection. This occurs within a particular environment or geographic location. Decent with modification is essentially the theory of inherited mutations that can alter the gene pool of a population, eventually resulting in speciation.

Natural selection is the unequal survival and reproduction of organisms resulting in the preservation of favorable adaptations. Natural selection favors individuals with higher biological fitness, which is defined by the individual's ability to produce viable offspring.

Convergent evolution is the independent evolution of similar structures among unrealted organisms as a result of similar environmental pressures. Evolution is any change in the proportions of different genotypes in a population from one generation to the next. Genetic drift is a change in the allele frequencies of a small population purely by chance. An adaptation is a characteristic of an organism that helps it survive and reproduce in a particular environment. 

Natural selection is a theory that explains that organisms better adapted to their environment will have a higher likelihood of survival. In the case of the giraffes, the height at which giraffes found leaves is the selective pressure. Assuming that the population has variable neck length, those that had neck lengths better suited for the height at which the leaves were at had better survival. This meant that those with necks that were either too long or too short were unable to reach the leaves as effectively, resulting in less survival. Therefore, the populations phenotypic frequencies will shift, favoring optimal neck lengths. The idea that ideal neck length would be reached within one's lifespan is Lamarkian, and was disproven. 

While observing South America aboard the Beagle, Darwin noticed how well animals were suited for their environments.  He also noted that the animals on the Galapagos were quite similar to those on the mainland, although they had differences that helped them thrive in their different habitats.  Due to the unity/similarity and yet the diversity of life, Darwin hypothesized that animals from the mainland colonized the islands.  From a few species, many more developed and evolved to fill the niches of the island. 

Directional selection occurs when conditions favor individuals exhibiting one extreme of a phenotypic range.  In this example, conditions on the island favor the birds with small beaks, which alters the population’s frequency curve for the phenotypic character in one direction (towards smaller beaked individuals).  Disruptive selection would act in favor both large and small beaks (phenotypic extremes), while stabilizing selection would act against both extremes. In other words, stabilizing selection would act in favor of medium sized beaks or those that lie in the median of the phenotypic curve. 

Maintaining a recessive allele that can cause a sickly phenotype when an individual is homozygous recessive does not seem advantangeous. However, if the recessive allele is maintained in one population over another, then it suggests that being heterozygous for this trait may produce a fitness benefit based on habitat.  As a result, it is not eliminated from the population. A similar example is sickle cell anemia in humans. In particular cases of sickle cell anemia, heterozygous individuals are protected from malaria while individuals that are homozygous have health problems. In other words, the fitness advantage associated with heterozygous carriers selects for maintining recessive alleles within the population.

Due to the fact that the blue beetles are toxic to the birds that prey on them, the birds will likely start to avoid the blue beetles and only eat the green ones. In this manner, natural selection selects against the green beetles and for the adaptations of the blue beetles. As a result, more blue beetles will survive and reproduce. Over time, this will lead to a population beetles that are mainly blue and toxic.

Stabilizing selection occurs when the individuals on both phenotypic extremes are selected against. In this case, individuals that are smaller or larger than the average possess a fitness disadvantage. THis scenario would result in stabilizing selection.