Quote by Frédéric Bouchard

“Thus, it appears that unicellulars are biological individuals whose cohesiveness presupposes the constant action of an immune system. According to the view defended in the previous sections, it means that they are true 'organisms'. If this is correct, it means that the reflection offered about the emergence and maintenance of individuality in multicellular organisms through the activity of an immune system needs in fact to be raised at the level of the much more ancient transition from independent replicators to the first prokaryotic cell. Because this transition is not very well known, and because basically nothing is known of the possible role of the immune system in this transition, I will leave this discussion for now, pending more experimental evidence in the near future. I think, though, that it raises the fascinating hypothesis that immunity has been a key element in both the evolutionary transition to multicellularity and the very ancient evolutionary transition to the first cell - often conceived of as the first 'true' biological individual. It also suggests that each cell in multicellular organisms like us may have its own immune system. RNA silencing has been convincingly described as the 'genome's immune system'. Within this perspective, one can conceive a hierarchy of immunological individuals, or 'organisms': a multicellular living thing like us is an organism insofar as it possesses an immune system, and in addition it comprises billions of cells, which themselves are organisms insofar as they each possess their own immune system. It is an attractive hypothesis, though it probably needs to be complemented by an analysis of the way in which the whole organism regulates immune responses at the level of each cell.”

Quote by Frédéric Bouchard