The key difference between sexual and natural selection is that natural selection acts on traits which increase fitness, whereas sexual selection favors any adaptation which enhances mating success. Differentiate between the two by choosing the example of sexual selection.

Sexual selection example; The brightness of the feathers of a peacock. You may also see similar traits in other birds, where some dance and show off bright feathers to attract a mate, where other build nests. These specific traits do not increase their chance of survival, and are not learned. They increase their fitness because they increase their chances of reproduction and passing on their genes.

Survival of the fittest = Survival of those who survive, and reproduce