The capacity to overproduce is a characteristic of all species but only a small fraction of offspring produced complete their development and reproduce successfully to leave offspring of their own.
individuals of a population vary extensively in their characteristics; no two individuals are exactly alike
(Observe. 1-3) production of more individuals than the environment can support leads to a struggle for existence among the individuals of a population with only a fraction of the offspring surviving each generation.
(Observ.4-5) differential reproductive success- in which organisms with traits favored by the environment produce more offspring than do organisms without those traits= result in the favored traits being disproportionately represented in the next generation. This is what is meant by survival of the fittest- it had nothing to do with size or strength.