Speciation responds to reproductive isolation that is either caused by natural selection or genetic drift. The process of natural selection often trims down a population size, and the remaining individuals cause changes in the gene pool. On the other hand, genetic drift usually occurs in a small population by chance. Therefore, a small population size is likely to lead in speciation.

B. small population size

Genetic variation is often caused by several factors including mutations, random mating, and gene recombination, whereas polygenic traits can only affect the distribution of phenotypes in a particular population.

C. I and III only

Since the nature favors the middle-sized lizards than the small and large ones, it shows a stabilizing selection. It indicates that the individuals at the center have a higher fitness that the individuals at the end sides of the curve.

C. stabilizing section

If two species reproduce offspring at different times, this isolating mechanism is called temporal isolation.

A. temporal isolation

Genetic equilibrium is condition characterized by constant allele frequencies in a particular population. This event do not lead to evolution in the population.

A. genetic equilibrium

A gene pool consists of the sum of a population’s genetic material or genetic information.

E. gene pool

In biology, the term fitness represents an individual’s ability to survive life and to reproduce offspring. If an individual is able to live longer and reproduce more offspring in a given environment or condition, it has a high fitness.

A. Fitness

In his experiment, Mendel used pea plants that have a single-gene trait with a dominant and recessive inheritance pattern wherein each gene is controlled by two alleles.

B. Single-gene trait

In 1950, the graph shows a stabilizing selection. After 40 years, which is in 1990, the data in the graph indicates a disruptive selection. This means that the crabs in medium tan color have become less common, compared to the crabs in light tan and dark tan.

D. disruptive selection

Since the data in the graph shows a disruptive selection, it indicates that the nature favors the crabs in light tan and dark tan, which are on the either ends of the graph. This event made the crabs in medium tan color become less common since they appear more visible to predators; hence, they are more likely to be hunted and consumed.

D. A new beach color makes medium-tan crabs the most visible to predators.