Which factor does NOT contribute to the concept of fitness in natural selection?

The concept of fitness in natural selection refers to an organism's ability to survive and reproduce in its environment. This typically encompasses several factors, such as survival of the fittest, the ability to reproduce, and adaptability to the environment, as all these elements directly influence an organism's success in passing on its genes to the next generation.

The size of an organism does not inherently determine its fitness. While size can impact various aspects of an organism's survival (like predator avoidance and resource acquisition), it is not a definitive measure of fitness. Fitness is more accurately assessed by an organism's reproductive success and how well it can adapt to its environment over its lifetime. Thus, size may play a role in the ecological dynamics of certain species, but it does not directly contribute to the concept of fitness in the context of natural selection.