Fitness is defined as the ability of an organism to adapt to new environmental situations. This means that an individual organism that is able to survive and reproduce in a changing environment has a higher fitness level than one that cannot. Fitness is also related to the quality of offspring produced, as an organism with a higher fitness level will likely produce offspring that are also able to adapt and survive in their environment. Additionally, fitness is related to the number of genes contributed by an individual to the next generation, as an organism with a higher fitness level will likely pass on more of its genes to its offspring. Therefore, all of the choices are correct in defining fitness. It is important to remember that fitness is a crucial aspect of health for an individual organism, as it impacts its ability to survive and reproduce.