What does the term fitness refer to in evolutionary biology?

In evolutionary biology, the term fitness specifically refers to the ability of an individual to survive and reproduce in a given environment. Fitness reflects how well a particular genotype or phenotype is suited to its surroundings, which influences its chances of leaving offspring that carry its genetic material into future generations. This concept encompasses not only survival but also reproductive success, as being fit means more than just surviving; it includes the successful passing on of genes to the next generation.

This understanding of fitness goes beyond mere physical attributes or lifespan. While physical strength and lifespan may influence an individual's ability to thrive, they do not capture the holistic view of fitness that includes reproductive success, which is critical for natural selection. In essence, individuals that are better adapted to their environment are likely to produce more offspring, thereby enhancing their genetic contribution to the population over time.