The first theory of evolution of living has been advanced by Jean-Baptiste Lamarck in his Philosophie Zoologique in 1809. As its title indicates, it presents itself as a philosophical system, although it lays the essential foundation for understanding living organisms and their evolution. Fifty years later, in 1859, with the publication of The Origin of Species, Charles Darwin proposed a scientific explanation of evolution as a mechanism simple, with the principle of natural selection. Over time, the original theory of Darwin has been refined with the results of experiments and observations that biologists have made. The theory which is now consensus that the synthetic theory of evolution or neo-Darwinism.
The evolutionary nature of life for so long been discussed and is even questioned by some people outside the scientific community, but none of these objections to the theory of evolution is scientifically based. The scientific community has been overwhelmingly accepted the evolution of life as a fact proven by experience and observation on numerous occasions including:
- examination of fossils in paleontology, which shows the evolution of life forms through time
- the comparative anatomy highlighting the morphological similarities between different animals but
- the inheritance that explains the genetic variation from one generation to another
- comparative study of genomes of several organisms which shows the distance more or less important in the phylogenetic tree, allowing to track changes and isolation of different life forms
- the artificial selection that practiced by humans from animals and plants he has domesticated, is the implementation by the Man of the principle of natural selection.
If biology is so vast, it is because of the extreme diversity of life that comes in so many forms that can be difficult to discern commonalities. A hierarchy of living has still been achieved, which is the area of systematic and taxonomy. All living things are classified into three areas:
- the bacteria
- the archaea
- the eukaryotes.
Structure in 3D of the molecule of DNA
Although different, all life forms share common characteristics. This suggests that life on Earth originated in a single life form, referred to as the acronym of LUCA (for Last universal common ancestor), which would have appeared on Earth there are at least 2.5 billion 'years.
The main characters are universal life:
- the carbon, which by its physical characteristics serves as a "template" to all organic compounds;
- the DNA and the RNA, which support the genome and provide translation of the latter to the offspring during reproduction;
- the cell is the smallest living unit. This last point is discussed within the scientific community, because viruses are considered alive by some biologists as they have no cells.