Final answer:
The heritability of a trait is controlled by genetics and environment. Genetics provide the heritable material, while environmental interactions influence the expression of those genetics in the phenotype. Selection strength affects how genetic variance is acted upon in a population over time.
Step-by-step explanation:
The heritability of a trait is determined by two primary factors: genetics and the environment. While genetics provide the blueprint for the traits and behaviors by defining alleles and genotype, it is the interaction with the environment that influences how these genetic potentials are expressed, called the phenotype. Not all variation can be passed down to offspring; only genetic variance is heritable and therefore subject to natural selection.
Environmental factors, such as temperature, nutrition, and sun exposure, can greatly influence the expression of genetic information in the phenotype but do not change the underlying genotype. This interaction highlights the complex relationship between nature (genes) and nurture (environment), playing a significant role in population dynamics and evolutionary pressures, such as selection strength. It is within this context that we understand an organism's traits and their potential changes over generations.
Summarily, while both listed factors in the question are indeed influential, the correct answer to which two factors control the heritability of a trait are genetics and environment. Selection strength is a factor in evolution, but it applies to the process of natural selection acting on the genetic variance within the population, not directly on the heritability of an individual trait.