The evolution of the species is the phenomenon of change, not necessarily in the best way, of the phenotype, visible and direct expression of individual species of the genotype.

J.B. Lamark was one of the first scientists proposing an evolution theory. His theory was based on some principles: There is a spontaneous attitude of living beings to become more complex; The principle of use and non-use; The inheritance principle of the acquired characters.

In each environment the individuals of each population are in competition among them to reach natural resources. In this surviving fight, the environment operates a selection called natural selection.

The evolution theory of Darwin is based on five important observations: The species are equipped of a large fertility and products. Some descendants can reach the adult stage; Populations of each species include about the same number of individuals; Food resources are limitated, but relatively constant during the time; Identical individuals are not produced by sexual reproduction. There are plenty of changes; A lot of these changes are due to the inheritance principle.

This is why Darwin, in his book “The origin of species”, says that: In a world which has stable populations, where each individual has to fight for surviving, the living beings (gifted with the best characteristics) will have more possibilities to survive and so to transmit their descendants the favorable characteristics. From generation to generation the advantageous characteristcs will become dominant among populations. This is the natural selection that can produce some changes in a population, leading to the formation of new species (speciation). He said also that fossil documentation can be an important support to his observations, being itself a demonstration of the process. Finally, he theorized that every living species was a descendant from an old common ancestor. The modern test of DNA supports and attests this idea.

This work has been produced by: Nicola Berloco Francesco Careccia Annalisa Poggiani Valeria Reale