Evolution happens to populations, and is the direct result of bell curve traits in a changing environment. Over time certain traits provide individuals advantage. These individuals thrive, and produce offspring who pass on the trait to their children. Consider a child who grows up with a father. Data clearly shows that this child is going to be more successful than his fatherless peers. The fathered child will be capable of producing more, higher quality, children. He will likely be the boss of his unfathered peers. High school biology defines success as being directly tied to quantity of reproduction, but in college you learn that quality is also important. Evolutionary fitness is the result of resource gathering, social interaction, reproductive bottlenecks and epigenetic adaptations.