Living creatures are divided into species. Over time (which may be comparatively short or very long) species change, i.e. they evolve. There are several essential components to natural evolution. Individuals (e.g. animals or plants) within a species population are different. As a result, some live longer and are more likely to have children that survive to adulthood than others (natural selection). These animals (or plants etc.) are said to be fitter (cf. “survival of the fittest”). Sometimes the variation has a genetic component, i.e. the children may inherit it from their parents. Consequently after a number of generations the proportion of individuals within the species with this favourable inheritable characteristic tends to increase. That is, over time the species as a whole changes or evolves.
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