What is Evolution?

Evolution is a change in the gene frequencies for a population (Belmont, Calif, 1984). Natural selection is the central idea of evolution. It means that organisms who can match better in nature and its changes are more likely to survive and pass their characteristics to the next generation. It is extremely important to pass the advantage that the organism has to the next generation so it can survive, otherwise for instance, there is no point for somebody to live till 120 but don't has a child.

Changes in nature could be for example, overpopulation of a specie, changing environment, predators, etc. There are three types of natural selection: stabilizing, directional and disruptive.

In stabilizing selection individuals with the average form or median of a trait have the highest strength, anything which selects against the average is not stabilizing selection. For example, Robins typically lay four eggs, because two might not be enough and 6 can be feed, but four is balanced. On the other hand, directional selection tends to be more outside the average.

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The opposite selection of the original population, it tends to be extreme in one direction left of right of the average curve. This selection is often seen in changes in weather, climate, food availability, etc. in general environmental changes. For example, the peppered Moth population of England during the Industrial revolution, darker coloured were well camouflaged, so they couldn't get eaten by birds like the lighter colour.

Lastly, the third is disruptive selection still refers to the extreme variation of a trait, are more likely to survive and pass out the gens.

Basically, the more average the worse could fit, only extremes survive. That creates two alternatives and split the population into two. For example, small fish can hide from the predators and hide their eggs, as well as big fish are strong to not be eaten and protect their eggs, but medium size fish can't protect their eggs nor hide easily.

To conclude, the natural selection occurs when the species must pass their gens and more specifically their most well-suited characteristics. In the stabilizing selection more average to the population of the specie the better can survive, the directional and disruptive are better, for the specie, to be extreme from the original population, either one way or both ways from the average because the average can't help them to survive and pass out the gens.