Natural currencies
If we refer to the
definition of what currencies are, we can observe that currencies have been invented by the nature a long time before humanity.
Granular structures such as hormones, photons, spores, electrons, or vibratory signals such as light, nervous transmission, can be considered as natural technologies for transacting, measuring, capitalizing. Our own bodies are using such system for their internal economy, i.e. exchange, regulation and balance.
Because monetary systems are a universal function of the living universe, it is quite normal that humankind has used this process for building its own social body.
Arthur Brock has written an interesting paper on these ideas, and has a name for this way of looking at currencies:
Operating System Earth