What defines a selection coefficient in terms of evolutionary biology?

The selection coefficient is a quantitative measure used in evolutionary biology to describe how much a particular trait or mutation affects the fitness of an organism compared to a baseline or reference group. Specifically, it represents the relative difference in fitness due to a mutation. A positive selection coefficient indicates that a mutation increases the fitness of an organism, while a negative selection coefficient implies that it decreases fitness.

This concept is crucial for understanding how natural selection operates within populations. When a mutation confers a survival or reproductive advantage, the selection coefficient quantifies that advantage, allowing researchers to predict how quickly that mutation might spread through the population. It's an essential tool for measuring the strength of selection acting on particular alleles or traits.

The other options do not accurately capture the essence of what a selection coefficient is. For instance, the rate at which new mutations arise doesn't relate to the measure of fitness differences. Similarly, referring to a selection coefficient as a multiplier of a selective variable lacks the specificity of addressing its role in defining relative fitness. Lastly, while it may seem intuitive to think of a coefficient as something that "kills organisms," this oversimplifies the concept and ignores the complexity of how traits influence survival and reproductive success.