How is "fitness" best defined in the context of evolution?

In the context of evolution, "fitness" is best defined as the ability of some individuals to be better suited for survival and reproduction. This concept encompasses more than just physical health or current reproductive capabilities; it emphasizes the relative advantages that certain traits confer that enhance an organism's likelihood of surviving in a specific environment and successfully passing on its genes to the next generation.

Fitness is shaped by various factors, including a species' specific environment, available resources, and interactions with other organisms. Those individuals with advantageous traits—such as better camouflage, superior hunting skills, or resistance to disease—will generally have higher reproductive success compared to their peers, thereby increasing the frequency of those traits in subsequent generations.

While the ability to reproduce is an important aspect of fitness, it is not solely about reproduction at any given time, but rather about the overall effectiveness of an individual in contributing to future generations. Therefore, focusing on the broader definition of fitness that includes the interplay of survival and reproduction better captures the essence of how evolution operates. This understanding underscores the adaptive nature of species and highlights the dynamic process of natural selection.