Final answer:
The sum total of an individual's direct and indirect fitness is known as inclusive fitness, which includes their relative ability to survive, reproduce, and pass on genes to future generations either directly or indirectly through relatives.
Step-by-step explanation:
The sum total of an individual's direct and indirect fitness is known as inclusive fitness. This concept revolves around an individual's ability to survive and reproduce relative to the rest of the population, often referred to as relative fitness. Direct fitness pertains to an organism's success in passing genes on through its own offspring, while indirect fitness refers to the success of passing genes indirectly, such as through the support of relatives' offspring. Scientists measure fitness to understand how different traits contribute to the success of individuals in their environments, and thus, how populations evolve over time. More adapted individuals are more likely to survive and pass their traits on to the next generation, influencing the evolutionary (Darwinian) fitness of the population.