They are the most common beings on earth. They have possibly been around as long as biological life has existed. They are considered dangerous and deadly – but they are much more than that. They are everywhere. Viruses.

Species of species renews our representation of the tree of life and reveals to us that the millions of species that inhabit the planet, ours included, all belong to a single and immense family. How to classify living species? What criterion should be used to sort them? The number of legs? The presence of wings, feathers, hair, scales? Not so simple...