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
It is the natural/genetic ability of an organism to avoid or repel attack by biotic agents (pests etc.) or to withstand the effects of abiotic agents example (chemicals).
