Pressure of selection

In the theory of the evolution, the concept of pressure of selection indicates a phenomenon which results in an evolution of the alive species subjected to certain environmental constraints. In a coloured way, one can see these environmental constraints like a force which " pousse" the species to be changed in a given direction, from where the term of pressure .

One can distinguish two principal types of pressures of selection:

pressures of selection exerted by the others living beings pertaining to the ecosystem known as biotic pressures (Predatory S, Parasite, candidate)
pressures of selection due to not-alive factors (like the chemical composition of the environment, the Temperature, etc) known as abiotic pressures .

The extreme conditions of life in the Désert are an example of abiotic pressure of selection: in order to protect itself from heat and the Dehydration, the species which occupy this ecological niche developed for example mechanisms of internal temperature control of the body.

The solutions which the various species subjected to identical pressures of selection reached are sometimes so similar that one speaks about evolutionary Convergence. It is the case for example profile Hydrodynamique very similiaire of the Requin S and Dauphin S: whereas the first are Poisson S cartilagineux, the seconds are Mammifère S marine but these two groups of species are subjected to similar pressures of selection which support the individuals moving in the most effective way in the aquatic environment.

A posteriori, the pressures of selections are reflected in the adaptations which a species given during its evolution presents. It is necessary however to keep in mind that they are the individuals who are subjected to pressures of selection and not the species in itself, which would return to a form of Sélection of group. In fact, the pressures of selection can be intra-species, i.e., between individuals of the same species. It is for example the case in the sexual Sélection: a pressure of important and relatively widespread selection at the vertebrate ones appears by a tendency for the males to increase their body mass, indeed the male individuals largest have more reproductive success.

Lastly, it should be noted that the multiple pressures of selection which are exerted on the individuals of a species can have antagonistic effects. The sexual selection supports for example the Paon S males carrying an exuberant tail but the Natural selection, via the threat of the Prédateurs, supports on the contrary the individuals more with same to move effectively and to be dissimulated in the environment.

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