SCIENCE

SENDING DNA MESSAGES TO FUTURE CIVILISATIONS

Dr Jonathan Cox, University of Bath, on 26 January 2001

In January last year, a very interesting note entitled "A Y3K Bug" appeared on the editorial page of the journal Nature Biotechnology. The note described a submission to a New York Times Magazine competition to create a time capsule in which every 1999 issue of that periodical would be sent to citizens of the year 3,000. The submission, made by a virtual-realist, a neuroscientist and a technical illustrator, suggested encoding the magazine in the four base format of DNA. Once the DNA encoding the magazine had been assembled, they suggested it could be used to replace the introns of cockroaches, and the cockroaches bred to create a living message in a bottle. In commenting on this idea (which sadly did not win the competition), the Nature Biotechnology note highlighted the fact that DNA was an extremely good storage medium (after all, life on earth has employed it for nearly 4 billion years) unlikely to ever become obsolete.

The cockroach proposal raises some fundamental questions. For instance, what information would be transmitted? Also, can we be sure that the recipients of the message would recognise it as such and if so, would they be able to decrypt it? This last point is perhaps not as silly as it sounds - use of Egyptian hieroglyphics is thought to have stopped around 400 A.D., yet it took until the 19th century, the extremely serendipitous finding of the Rosetta Stone, and not a small amount of brilliance, to work out what they meant. Given that those who inscribed the hieroglyphics did not deliberately hide their meaning, devising a script that will be read and understood easily in a few thousand or even a million years' time would be a significant undertaking (we cannot assume that the future civilisation will read or speak English, or any other language currently in use).

Using the example of cuneiform to demonstrate what is required for a successful decipherment, the talk focused on how DNA might be used to encode a message that was glaringly obvious to anyone who sequenced that DNA. The achievements of Niebuhr, Duperron, de Sacy, Grotefend and especially Rawlinson were mentioned in connection with the decipherment of cuneiform. (Reference was also made to scripts which have not yet been successfully deciphered, such as the pictorial script which appears on the Phaistos disc, and it was emphasised that the language in which the script is written must be known in order to break into the script).

An example of a DNA cipher that might be used in the encryption process was presented. This prototype cipher was based on a suggestion the physicist George Gamow had made some years ago regarding the genetic code (his `combination code'). The cipher uses combinations of the three DNA bases in groups of three to represent each letter of the alphabet, with letters separated by the fourth base, and word divisions represented by a triplet of the fourth letter. For example, if the four DNA bases are A, B, C and D, the letter `a' might be represented by AAA, `b' by BBB, `d' by ABB, `x' by BAC etc. (note only A, B and C are used for the letters) and the letter divider could be D and the word divider DDD.

Jonathan Cox

Discussion

It was queried whether we should aim to communicate with a civilisation a million years hence or a thousand years. A long period is desirable because extinctions of most life on earth by disasters occurs infrequently. Astronomical and geological data is perhaps more important to store than cultural data. It was suggested that baked clay tablets had been shown to be durable for several thousand years and would be more obvious to future explorers than DNA, but for transmission through space to other civilisations, DNA would be more compact. A detailed discussion of the proposed code and others took place.

Donald Lovell

Bibliography

The Code Book by Simon Singh, 4th Estate, 1998

The Code Breakers by David Kahn, Scriber, 1996