How does natural selection affect reproduction?
If an organism has a trait that doesn't allow it to grow to maturity, this may prevent it from reproducing.
The classic example of this is the peppered moth. In the pre-industrial age, trees in Europe were light coloured so those moths with light coloration thrived and were able to reproduce and pass on this trait to the offspring. Consequently, if you were a dark coloured moth you would probably get eaten by birds or whatever and therefore never have the chance to reproduce. In the same example in Europe, when pollution discoloured the trees and made them dark coloured, the entire situation changed - dark coloration was in and light was out!