What is one key factor that leads to natural selection?

Natural selection is a process fundamental to evolution, driven largely by the existence of variation in traits among individuals in a population. This variation provides the raw material for natural selection, as it allows certain traits to be advantageous in a given environment. Individuals with traits that enhance their survival and reproductive success are more likely to pass on these desirable traits to the next generation, leading to a gradual change in the population over time.

In the context of the other choices, predetermined genetic makeup does not facilitate the adaptability necessary for natural selection, as it implies a fixed set of traits without variation. Neutral mutations do not significantly impact fitness or survival, and therefore do not contribute effectively to natural selection. Lastly, uniform survival rates across all species would imply no competition or differential survival based on traits, which contradicts the very essence of natural selection, where not all individuals survive equally based on their traits. Hence, the presence of variation is essential for the process of natural selection to occur effectively.