How does natural selection occur?

There are two important terms to understand (and state in an exam!) to answer this question. 1) Genetic diversity = the number of different alleles of genes in a population. Genetic diversity is a main factor that enables natural selection to occur. 2) Natural selection = process by which a species changes over time, in response to changes in the environment or competition between organisms, in order for the species to survive. Natural selection results in species that are better adapted to their environment, and is a main factor that allows evolution of populations over time.3) Adaptation = any alteration in structure or function of an organism or any of its parts that results from natural selection and by which the organism becomes better fitted to survive and multiply in its environment. These adaptations may be anatomical, physiological or behavioural.So how does natural selection occur? (this is an ideal 'framework' answer):1) Within a population, there are many individuals who possess different alleles of a gene.For example, in a population of giraffes, there may be a gene for 'neck size'. 2) A random mutation (or 'de novo' mutation) can result in new alleles of a geneFor example, in this giraffe population, certain individuals may have an allele for a 'long neck', others for a 'short neck'.3) This increases the genetic diversity of the population.4) It is important to note that many mutations may not be beneficial (or even harmful), but in certain environments the new allele of a gene might benefit its possessor.For example, the giraffes with a short neck may not be able to reach the leaves they eat at the top of trees (harmful), while the giraffes with long neck will (beneficial).5)The population with the beneficial allele will better be able survive (eat the leaves) and compete with other members of their population (for food). This is adaptation.6) ...Ultimately leading to increased reproductive success. 7) The advantageous allele is inherited by members of the next generation. Basically, the members of the species with the most desirable characteristics are able to produce the best-adapted offspring.8) As a result, over many generations, the new allele increases in frequency in the population.Keeping with the giraffe example, the baby giraffes will inherit the long neck gene and better be able to survive, grow and reproduce...9) And this continues in a cycle throughout generations...Tips:This is a commonly asked question so is very useful to 'learn off'. Usually how it is asked will be a short paragraph describing a population (e.g. giraffes) whereby a certain trait (e.g. long necks) has become common, and it would ask you to describe why this trait has become common... the answer is natural selection! It is useful to take a step by step approach, using a frameworkRemember this process involves POPULATIONS (not individuals) and TAKES A LONG TIME -over multiple generations- to occur.Use as much detail and key "buzzwords" (in bold) as possible - show off what you know!This brings me onto..Have a list of buzzwords from each topic, this will make answering questions a lot easier. Use examples - apply it from the question, because it is there to help you :)