Unit of selection

Unit of selection is the level at which natural selection acts in biological systems. Natural selection occurs when organisms that have certain traits are more successful at surviving and reproducing than those without those traits. Selection affects the frequency of traits in a population. The unit of selection is the level at which that selection occurs, such as a gene, an organism, or a group of organisms. For example, an individual ant may carry a gene that makes it more likely to survive in a certain environment. That gene would be the unit of selection, since selection acts on it and affects its frequency in the ant population.