Which process refers to the unique combination of traits passed down from one generation to another?

The process that refers to the unique combination of traits passed down from one generation to another is heritable variation. This concept is fundamental to genetics as it emphasizes the role of heredity in the transmission of traits from parents to offspring. Heritable variation occurs because individuals inherit different combinations of alleles, which leads to diverse expressions of traits within a population.

This variation is crucial for evolution, as it provides the raw material for natural selection to act upon. When certain traits confer advantages in survival or reproduction, they are more likely to be passed on to the next generation, ultimately influencing the genetic makeup of future populations. This process highlights the importance of genetic diversity and how it shapes the evolution of species over time.

The other options, while related to genetics and evolution, describe different mechanisms or processes that do not specifically refer to the unique combination of traits inherited between generations. Heritable variation focuses directly on the inheritance of traits, making it the most accurate answer in this context.