Final answer:
Increased selective pressure would increase the rate of evolution by natural selection for a particular trait.
Step-by-step explanation:
The correct answer is d. Increased selective pressure. Increased selective pressure would favor individuals with certain traits, increasing the rate at which those traits are passed on to future generations through natural selection. This can lead to the evolution of the trait over time. Decreased heritability (option a) would decrease the rate of evolution, as traits would be less likely to be inherited. Decreased genetic variation (option b) would also decrease the rate of evolution, as there would be less variation for natural selection to act upon. Increased environmental variation (option c) may increase the rate of evolution, but the most direct and impactful factor is increased selective pressure (option d).