Answer:
Natural selection is the method of differential survival and reproduction of the individuals in the population of the species, this occurs due to the difference in phenotype. The organism exhibiting the more favorable phenotype will likely to adapt the changes that occur around the surrounding environment and are likely to survive and reproduce. The favorable traits are passed over the generations. This ensures the evolution of species due to passage of traits which favors the survival of organism under unfavorable conditions. It can be said that some organism have better advantage of survival over the others due to natural selection.
The evolution of neck of the giraffe species, is the evidence of natural selection. The giraffe population in the initial stage of evolution experienced the scarcity of food, therefore the neck elongation initiated in order to derive leaves from the tree tops. The following points which supports the Charles Darwin's natural selection theory based on giraffe evolution:
Natural selection is the one of the mechanisms that causes evolution over time,
beneficial variations will be passed on to future generations,
some organisms in a population are better equipped to survive than others