Overproduction, variations, the constancy of population size, natural selection sequence was proposed by Darwin and Wallace for organic evolution.
Overproduction: There is an overproduction of organisms due to high reproductive rate, even when the resources are limited. Even though the population increases enormously, the number of individuals in every generation remains constant.
Variation: means differences, like you have black and white peppered moths, red, green capsicum and hundreds of colours of butterflies. And they are all different because they are adapting themselves, to be better than each other.
Natural selection: It states that nature creates struggle and selects those animals which win in the competition. The organisms which have useful variations will win in the competition. Whereas the organisms which have no such useful variations will die.