How does natural selection work?

Natural selection requires three criteria to be met:Offspring inherit some characteristics from their parentsParents have more children than will survive to adulthoodThose children that are better adapted to their environment are more likely to surviveWhen these are met, as they are in nature, the population of offspring that survive to the next generation will a selection of individuals that are, on average, better adapted to the environment than the previous generation, because those that are less adapted have not survived. The offspring of the new generation will inherit the characteristics of said generation and will also be more adapted to the environment than the original, now grandparent, generation. This pattern repeats, and over time, species can gradually evolve.