**Core Concept**
Population genetics is the study of the distribution of genetic variation within and among populations. It involves the analysis of genetic data to understand the evolutionary history, migration patterns, and other demographic processes that shape the genetic makeup of populations.

**Why the Correct Answer is Right**
Population genetics is closely related to evolutionary biology, as it seeks to explain the mechanisms by which populations change over time. This includes the study of genetic drift, gene flow, mutation, and natural selection, which are all key drivers of evolutionary change. By analyzing genetic data, population geneticists can reconstruct the evolutionary history of a population and understand how it has been shaped by various demographic and selective pressures.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because population genetics is distinct from molecular biology, which focuses on the structure and function of biomolecules at the molecular level.
**Option B:** This option is incorrect because population genetics is not primarily concerned with the study of individual organisms, but rather with the analysis of genetic variation within and among populations.
**Option C:** This option is incorrect because population genetics is not directly related to the study of disease epidemiology, although it may be used to inform epidemiological studies.

**Clinical Pearl / High-Yield Fact**
One key concept in population genetics is the Hardy-Weinberg principle, which states that the frequency of alleles in a population will remain constant over time in the absence of genetic drift, mutation, or gene flow. This principle is widely used in population genetics to predict the expected genotype frequencies in a population.

**Correct Answer:** D. Evolutionary biology