"I Am Not a Number - I Am a Free Man!"

Tagging objects with unique, artificial DNA sequences that act as a barcode is not new; but I had no idea that it had progressed to the point where it was almost routine, as in this collectibles tagging service. It works by marking the object with an invisible ink containing small quantities of a synthetic DNA tag.

Although the collectibles story mentions using lasers and fluorescence to authenticate the tag, a more scalable approach would be to read the DNA directly: that requires fast, cheap DNA sequencers, and there's plenty of those under development.

As the cost of DNA synthesis and sequencing plummets, so this kind of barcoding is likely to become common. It's easy to apply, does not disfigure the object as a conventional barcode does (to say nothing of an RFID chip), and so does not need to be removed when the customer takes the item home.

But there is a dangerous downside to this ingenious approach. It will make the idea of DNA tagging uncomfortably mundane. And once people are used to the practice in their daily lives, it's only a short step for companies and governments to move on to identifying people by some very special sequences of DNA - their own.

The big advantage is that you don't even need to apply the invisible ink: practically every cell in our body already has the DNA tag. That tag is unique (modulo the odd identical twin), and you can't change your underlying genomic sequence (local mutations aside). In effect, this DNA forms your very own permanent identification number - written in the quaternary digits A, C, G and T - that is ideal for key documents like passports, driving licences and health cards. What government could pass up the opportunity to adopt such a logical approach?

Moreover, because the number never changes, you leave behind in your life a continuous trail of DNA tags - in the form of discarded cells (hair, skin, saliva, blood) - that forms a complete record of where you went. Put another way, for any given event, governments will be able confidently to assign names to most of the people who were involved, as well as to innocent witnesses - sorting out which is which is merely a forensic detail - on the basis of the genomic calling-cards they inevitably leave behind.

So much for freedom, Number 6.