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Natural Selection The necessities of evolution are survival and reproduction. According to the theory of natural selection, these two aspects of living organisms determine the path of their biological evolution. When certain individuals in a population possess traits that help them to adapt more easily to their environment, they stand a better chance to survive, and reproduce more offspring. These traits are then passed on to the next generation, and may eventually lead the evolution of a new species. These adaptations, or winning traits, occur because organisms of the same species are capable of variations. Variations can both help or hinder the growth of organisms. The crux of the theory of natural selection states that nature tends to eliminate organisms with hindering variations, and favours those with helping variations, which are better known as adaptations. Evolution occurs within species and population, as well on a larger scale among groups of species. To differentiate between the two types of evolution, biologists refer to small-scale changes as microevolution, and large-scale changes as macroevolution. In other words, microevolution leads to macroevolution.
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