Natural selection and evolution

The Earth has a long history and all organisms, man included, originated during history and came after other forms of life. As a consequence, all species derive from other species, and all living beings have a common ancestor in the past. This was all possible because in time a series of changes occurred having an influence on species: this is evolution.
Lamarck and Darwin
Jean-Baptiste Lamarck, a French scientist (1744-1829) thought that the environment is the cause of evolution as it forces animals to use some parts of their body instead of others. With time passing, those parts of the body that are not used tend to disappear, while the most used ones develop more.
The English naturalist Charles Darwin (1809-1882) defined the natural selection process by stating that the interaction between individuals and the environment generate two different situations: some animals do not manage to survive while others survive and reproce themselves, transmitting to their offspring the variations that allow them to survive in that specific environment. This variability of individuals can be inherited and is expressed genetically.
Genetical variability is the basis for evolutionary changes, and almost all species show to change genetically, if they are assessed in time in the same place, but also if different placet are compared.
To understand it better
According to Lamarck, giraffes gradually stretch their neck to eat the leaves from the trees and transmit this modification from one generation to another. According to Darwin, inside a group of giraffes with a short neck one was born with a long neck. This long-neck giraffe was facilitated in reaching the leaves and therefore could eat better. As a consequence, that giraffe became stronger and more robust than the others. That different giraffe had been subject to a mutation of the gene that determines the neck characteristics. Since it was an advantageous characteristic, in time it spread to the whole species. This was possible because the children inherit the characteristics of their parents.

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