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The mechanism of evolution.
Evolution is not a modern concept. Since ancient times, a number of philosophers and naturalists (including Confucius and Aristotle in Greece) have suggested that complex species evolve from simpler pre-existing ones by a process of continuous and gradual change. However, it was not until the 19th century that scientists came up with plausible mechanisms for evolution. The mechanism that is widely accepted among biologists today is called neo-Darwinism. It is modern theory based on the work of the nineteenth- century naturalist Charles Darwin.
Darwin’s theory was based on three main observations: 1. Within a population are organisms with varying characteristics, and these variations are inherited (at least in part) by their offspring. 2. Organisms produce more offspring than are required to replace their parents. 3. On average, population numbers remain relatively constant and no population gets bigger indefinitely. From these observations, Darwin came to the conclusion that within a population many individuals do not survive, or fail to reproduce. There is a “struggle for existence”. For example, members of the same population compete to obtain limited resources, and there is a struggle to avoid predation and disease, or to tolerate changes in environmental conditions such as temperature. In this struggle for existence those individuals that are best adapted to their environment will have a selective advantage: they will be more likely to survive and produce offspring than less well-adapted organisms.
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