"Biological diversity means the variability among living organisms from all sources [...] this includes diversity within species, between species and ecosystems".
Convention on Biological Diversity, Article 2.

Biodiversity refers to all forms of life on our planet and involves three different but interdependent levels :

• Genes. Genetic variation between members of the same species (intra-species variation) explains the  unique character of every living being.
• Species. Including everything from animals and plants to fungi and micro-organisms (algae, bacteria, etc.).
• Ecosystems. These are dynamic complexes made up of a non-living milieu (the biotope), the organisms that inhabit that milieu (the biocenoses) and the interaction between the two.

Little-known living species

Main groups of species described

Source : Total / France's National Museum of Natural History

Scientists estimate that taxonomists have so far only described 1.75 million of the 14 million species thought to exist on our planet.

The animal kingdom accounts for three quarters of the species described so far, with insects alone making up half of the number. Scientific knowledge of higher plants and mammals is regarded as relatively satisfactory, but our knowledge of insects and fungi is still far from complete. Thousands of plants and animals will never be observed/described because they are disappearing faster than they can be identified.
About 10,000 new species are described each year.

Respect for the unknown and its extensive potential
Adaptation
As most living species on Earth have yet to be identified, it is difficult to evaluate their impact on the global environment and the effective role they play. However, the fact that there is broad genetic diversity present can only improve the chances of living species adapting to changes (climatic, ecological, etc.) in their environment.

Inspiration
Bionics, which is a science based on the observation of Nature, allows scientists to understand and to translate the way living beings function into scientific and technological applications. As early as 1890, Clement Ader used the bat as inspiration in building his “Eole” flying machine, while the materials used to coat today’s competition swimsuits and divers'flippers are modelled respectively on the skin of the dolphin, and its caudal fin.  

Health
Biodiversity also provides humankind with food and medicines. More than half of the substances used by the pharmaceuticals industry are derived from plants and animals. Major research programmes are now under way, focusing particularly on fungi, which contain a number of active substances that may be effective against various types of illnesses, notably cancer and diabetes.

Enrichment
Last but not least, biodiversity enhances the richness and the beauty of the landscapes that surround us, making life more pleasant for all.
In short, it is important that we protect all living species, each of which carries and transmits its specific genetic heritage. It is also vital to preserve the ecosystems that provide a framework for both intra-specific and inter-specific diversity. Tropical rain-forests, for example, are home to more than half the living species identified on Earth so far. And coral reefs alone are home to about 25% of our planet’s living marine species. Because of the less favourable abiotic factors in play (temperature, water, light, soil, wind), extreme milieus such as deserts, the ocean depths and mangrove zones are usually home to endemic species, i.e. plants and animals found nowhere else.