What is an organism? We tend to see organisms as bodies, composed of cells coming from the same origin and therefore sharing the same genome. It is getting progressively clear that this conception is an inappropriate reduction of a far more complex reality. While we know through the work of Mereshkowski (1905) and Margulis (1970) that already the building blocks of these bodies, cells, are functional, rather than genetic units, we are still far from appreciating that also organisms are not genetic, but functional units that often house life forms of completely different provenance.