Natural selection refers to the varying frequency of genes in a population because of the differential success in reproduction and survival of different genotypes. The traits which are the most common in a population are the traits originating from the predecessors which left the most descendants. This is the result of natural selection in action.
Natural selection is the primary driving force of evolution. It is a mechanism which causes diversity in different environments. Although the concept was first introduced by Charles Darwin in 1859, it wasn’t until around the 1930s that biologists begun to accept this theory.
The ability of natural selection to drive evolution depends on their being variation between individuals and this variation needs to be heritable. There is variation in the behavioural, morphological and physiological traits of organisms and these are traits which all affect survival. Thus, natural selection can act on all of these traits.
Evidently natural selection acts on traits, not on individuals or the population at large. Natural selection favours the traits which are advantageous and promote an individual’s ability to survive and reproduce. It is these traits which get selected for and passed on through natural selection. Although genetic variation comes from mutations, sexual reproduction and the interaction between genes and the environment, it is natural selection promoting which genes become the most common over subsequent generations.
Furthermore, natural selection is also an observable phenomenon. Bacterial resistance to antibiotics is an example. Bacterial infections are fought with antibiotics, but sometimes, especially when the duration of the drug is short, some bacteria will have randomly obtained mutations making them less susceptible to the drug. Once the drug is stopped, if these bacteria survive, natural selection will favour these new traits increasing microbial resistance for that drug.