Here's why:

* Natural selection is about survival and reproduction: It's not just about surviving longer, but about surviving long enough to reproduce and pass on your genes.

* Differential reproduction means some individuals have more offspring: This is driven by variations within a population. Individuals with traits that make them better suited to their environment are more likely to survive, reproduce, and pass those traits on to their offspring.

* Over time, beneficial traits become more common: As the individuals with the advantageous traits produce more offspring, those traits become more prevalent in the population, leading to evolution.

In short, natural selection favors individuals that are better at reproducing, not just surviving.