Theory of Evolution: Descent with Modification by Natural Selection
Our modern theory of evolution was proposed by Charles Darwin and consists of mainly two parts: Evolution is a "Descent with Modification" and it happens through natural selection.
Descent with Modification
In wildlife, all the species tend to produce more offspring than can possibly survive in the competition. Therefore a "struggle to survive" occurs and only those most fit to the environment can survive and reproduce. In addition, among the offspring usually many variations in all traits of the species are found (due to mutation, gene flow, genetic drift). Some variations make the offspring more suitable ("fit") to the environment and are more likely to survive (survival of the fittest). In reverse, those variations less fit to the environment are more likely to die. This process is also called natural selection.
Types of Natural Selections
There are 3 types of natural selections that change a population.
1. Stabilizing Selection
Descent with Modification
In wildlife, all the species tend to produce more offspring than can possibly survive in the competition. Therefore a "struggle to survive" occurs and only those most fit to the environment can survive and reproduce. In addition, among the offspring usually many variations in all traits of the species are found (due to mutation, gene flow, genetic drift). Some variations make the offspring more suitable ("fit") to the environment and are more likely to survive (survival of the fittest). In reverse, those variations less fit to the environment are more likely to die. This process is also called natural selection.
Types of Natural Selections
There are 3 types of natural selections that change a population.
1. Stabilizing Selection
In a Stabilizing Selection, the most common variation of the species becomes even more common and there are less extremes.
2. Directional Selection
2. Directional Selection
In a Directional Selection, one extreme variation is more fit and survives and reproduces more than the former intermediate variation.
3. Disruptive Selection
3. Disruptive Selection
In a Disruptive Selection, two extremes are more fit than the intermediate variation. Therefore, the intermediate amount of organisms decreases because it is harder to survive and the amount of extreme variations increases.
The Evolution of a Human