What is the key factor that determines the survival of individuals according to Darwin's theory?

The key factor that determines the survival of individuals according to Darwin's theory is the presence of genetic traits that enhance survival. This concept is central to the theory of natural selection, where individuals with advantageous traits are more likely to survive and reproduce in their environment. Such traits can include physical characteristics, behavioral adaptations, or physiological mechanisms that improve an organism's chances of finding food, escaping predators, or coping with environmental challenges. Over time, these advantageous traits become more common in the population as those individuals with the traits pass them on to their offspring. This process leads to evolution as species adapt to their environments based on the success of those genetic traits. In this context, while factors like food availability, climate adaptability, and population size can influence survival, it is the inherited genetic characteristics that fundamentally drive the process of natural selection.