The five steps of the process of natural selection are variation, inheritance, selection, time and adaptation. Each step is indispensable to the process, and each has been observed either in nature, the laboratory or both.
The first element of natural selection is in the natural variation among organisms. Variation can be extremely subtle, such as a slight difference in camouflage patterns or minor differences in metabolism, but it serves as the raw material of evolution. The variable traits must, in order to be truly subject to selection pressure, be heritable. A trait is heritable if it can be passed from parents to offspring. This permits natural selection to work on multiple generations. Selection is the third element, and it consists of the differential rates at which subtly different lineages breed, survive and die. The selective pressures felt by populations are usually weak from one generation to the next, which is why the fourth element, time, is important. Evolution takes many generations to show noticeable effects, and new traits take time to achieve fixation in populations. The traits that survive the process of evolution are generally adaptive, which means they confer some advantage on their bearers. These proliferate at the expense of less-advantageous traits and increase the inclusive fitness of the gene pool in its environment.