THE TELEPHONE EXCHANGE OF LIFE
There is no spirit-driven life force: we are just bytes and bytes and bytes of
digital information, argues Richard Dawkins I DON'T usually drop names but on occa- sion the temptation is severe. Francis Crick and James Watson happen, inde- pendently, to have been our dinner guests these past two weekends and I have been reflecting on their importance to this cen- tury's culture.
Writing of their joint achievement, the discovery of what genes exactly are, the great scientist and polymath Sir Peter Medawar said, 'It is simply not worth arguing with anyone so obtuse as not to realise that this complex of discoveries is the greatest achievement of science in the twentieth century.'
Medawar's remark, for some, will typify the arrogance of science, and arrogance is a charge which, at one time or another, both Watson and Crick have faced with equanimity. Medawar may have gone too far, but not much too far and the point is one that can be defended. If I were to undertake a defence I should not appeal to the immense medical and other practical benefits that have followed, and will increasingly follow, from what those two young men did in 1953. I should make an altogether more radical claim. This is that Watson and Crick delivered the final, killing blow to vitalism in all its forms. Up until 1953 it was still possible to believe that there was something deeply and irre- ducibly mysterious in living protoplasm. No longer. Even those philosophers who had been predisposed to a mechanistic view of life would not have dared hope for such comprehensive fulfilment of their wildst dreams. We can get an inkling of this from a somewhat surprising source — an analo- gy with digital telephones.
Gramophones, most tape-recorders and, until recently, most telephones, have used analogue codes. Compact discs, computers and most modern telephone systems use digital codes. In an analogue telephone system, continuously fluctuating waves of pressure in the air (sounds) are transduced into correspondingly fluctuating waves of voltage in a wire. At the other end of the line these voltage waves are reconverted, by a vibrating membrane in the earpiece, directly back into the corresponding air pressure waves so that we can hear them. The code is a simple and direct one: elec- trical fluctuations in wire are proportional to pressure fluctuations in air. All possible voltages, within certain limits, may pass down the wire and the differences between them matter.
In a digital telephone, only two possible voltages, or some other discrete number of possible voltages such as eight or 256, pass down the wire. The information lies not in the voltages themselves but in the pattern- ing of discrete levels. This is called Pulse Code Modulation. The actual voltage at any one time will seldom be exactly equal to any of the eight, say, nominal values, but the receiving apparatus will round it off: will assume the nearest of the expected voltages. You can arrange things so that what emerges at the other end of the line can be well-nigh perfect even if the trans- mission along the line is poor. All you have to do is set the discrete levels far enough apart so that random fluctuations can never be misinterpreted, by the receiving instrument, as the wrong level. This is the great virtue of digital codes and it is why audio systems, video systems and informa- tion technology generally are increasingly going digital.
The sounds that enter the mouthpiece of a digital telephone and leave the earpiece are still analogue fluctuations in air pres- sure. Actually, the waves from your voice stay analogue, as a voltage fluctuating in a wire, until they reach the local telephone exchange. It is the information travelling from exchange to exchange that is digital. Some kind of code has to be set up to translate analogue values, microsecond by microsecond, into sequences of discrete pulses — digitally coded numbers. When you plead with your lover over the tele- phone, every nuance, every catch in the voice, every passionate sigh and yearning timbre, is carried along the wire solely in the form of numbers. You can be moved to tears by numbers . . . provided they are encoded and decoded fast enough. Mod- ern electronic switching gear is so fast that the line's time is divided into slices, rather as a chess master may divide his time between 20 games in rotation. By this means, tens of thousands of conversations are slotted into the same telephone line, apparently simultaneously yet electronical- ly segregated without interference.
The deficiencies of analogue signals don't matter too much as long as they aren't copied repeatedly. A tape-recording may have so little hiss on it that you hardly notice it. But if, say, you make a tape of the tape, then a tape of the tape of the tape . . . after 100 'generations' a horrible hiss will be all that remains. Something like this was a problem in the days when telephones were all analogue. Any tele- phone signal fades over a long wire and has to be boosted — reamplified — every hundred miles or so. In analogue days this was a great bugbear because each amplifi- cation stage increased the proportion of background hiss. Digital signals, too, need boosting. But, for the reason we've already seen, the boosting does not introduce any error: things can be set up so that the information gets through perfectly, no matter how many boosting stations inter- vene. Hiss does not increase even over hundreds and hundreds of boosted miles.
I learned as a child that nerves are the telephone wires of the body, but are they analogue or digital? A mixture of both. Each nerve cell communicates via a long thin tube along which waves of chemical change pass — like a trail of gunpowder fizzing along the ground. Except that, unlike a trail of gunpowder, the nerve soon recovers and can fizz again after a short rest period. The absolute magnitude of the wave — the temperature of the gun- powder — may fluctuate as it races along the nerve, but this is irrelevant. The code ignores it. Either the chemical pulse is there or it is not, like two discrete voltage levels in a digital telephone. To this extent the nervous system is digital. But nerve impulses are not dragooned into bytes: they don't assemble into discrete code numbers. Instead, the strength of the message (the loudness of the sound, the brightness of the light, maybe even the depth of the emo- tion) is encoded as the rate of impulses. Engineers know this as Pulse Frequency Modulation and it was popular with them, as an intermediate technology, before Pulse Code Modulation was adopted .
A pulse rate is an analogue quantity, but the pulses themselves are digital — they are either there or they are not, with no half measures. And the nervous system reaps the same benefit from this as any dig- ital system does. Because of the way nerve cells work, there is the equivalent of an amplifying booster, not every hundred miles but every millimetre — 800 boosting stations between the spinal cord and your fingertip. If the absolute height of the gun- powder wave mattered, the message would be distorted beyond recognition over the length of a human arm, let alone a giraffe's neck. Digital coding offers the only solu- tion, and natural selection has duly adopt- ed it.
The most revolutionary consequence of Watson and Crick's discovery is that the genes, too, are seen to be digital. We already knew, from the work of the Mendelians beginning in the last century, that heredity was particulate. But this just meant that you either have a gene or you don't. Genes from your mother and your father don't mingle with each other on their way through you to your children. Every gene in a child comes from one, and only one, of its four grandparents, and from one and only one of its eight great- grandparents This is digital, certainly, but only at a gross level. After Watson and Click, we know that genes themselves, within their minute internal structure, are long strings of pure digital information. What is more, they are truly digital in the full and strong sense of computers and compact discs, not in the weak sense of the nervous system. It is not a binary code, as in computers, but a quaternary code. Apart from this, the machine-code of the genes is uncannily computer-like.
The following science fiction plot is fea- sible, using a technology that differs from today's only in being a little speeded up. Professor Jim Crickson has been kid- napped by an evil foreign power and forced to work in their biological-warfare labs. To save civilisation, it is vitally impor- tant that he should communicate some top-secret information to the outside world, but all normal channels of commu- nication are denied him. Except one . The DNA code consists of 64 triplet `codons', enough for a complete upper- and lower-case English alphabet plus a space character, ten numerals and a full stop. Professor Crickson takes a virulent influenza virus off the laboratory shelf and engineers into its genome the complete text of his message to the free world, in English.
He repeats his message over and over again in the engineered genome, adding an easily recognised 'flag' sequence, say the first ten prime numbers. He then infects himself with the virus and sneezes in a room full of people. A wave of flu sweeps the world and medical labs in dis- tant lands set to work to sequence its genome, in an attempt to design a vaccine. It soon becomes apparent that there is a strange repeated pattern in the genome. Helped by the prime numbers — which cannot arise spontaneously but only by deliberate intention — somebody tumbles to the idea of applying simple code-break- ing techniques to it. From there it would be short work to read the full English text of Professor Crickson's message, sneezed around the world.
Our genetic system — which is the uni- versal system of all life on the planet — is digital to the core. With word-for-word accuracy, you could encode the whole of the New Testament in those parts of the human genome that are at present filled with 'junk DNA' — that is, DNA that is never used in the ordinary way by the body. Every cell in your body contains the equivalent of 23 immense data tapes, reel- ing off digital characteis via numerous reading heads working simultaneously. The tapes themselves contain the same information in every cell, but the reading heads in different kinds of cells seek out different parts of the database for their own specialist purposes. That is why muscle cells are different from liver cells. There is no spirit-driven life force, no throbbing, heaving, pullulating, protoplasmic mystic jelly. Life is just bytes and bytes and bytes of digital information.
Genes are pure information, information that can be encoded, recoded and decoded, without any degradation or change of meaning. Pure information can be copied and, since it is digital information, the accuracy of the copying can be immense. DNA characters are copied with an accura- cy that competes with the best that modern engineers can do. DNA letters are copied down the generations, with just enough occasional errors to introduce variety. Among this variety, those coded combina- tions that become more numerous in the world will obviously and automatically be the ones that are most 'successful'. What does 'successful' mean? It means those DNA messages which, when decoded and obeyed inside cells, make those cells com- bine into bodies which take active steps to preserve and propagate those very same DNA messages. We — and that means all living things — are survival machines pro- grammed to propagate the digital database that did the programming. Darwinism is now seen to be the survival of the survivors at the level of pure, digital code.
With hindsight, it could not have been otherwise. An analogue genetic system could be imagined. But we have already seen what happens to analogue informa- tion when it is recopied over successive generations. It is Chinese Whispers. Boost- ed telephone systems, recopied tapes, nerve cells, photocopies of photocopies all analogue signals are so vulnerable to cumulative degradation that copying can- not be sustained beyond a limited number of generations. Genes, on the other hand, can self-copy for 10 million generations and not degrade. Darwinism only works because, apart from discrete mutations which natural selection can positively weed out or preserve, the copying process is per- fect. Only a digital genetic system is capa- ble of sustaining Darwinism over the wastes of geological time. 1953, the year of the double helix, will come to be seen not only as the end of mystical and obscuran- tist views of life. Darwinians will see it as the year their subject went digital.
Richard Dawkins is author of The Selfish Gene and fellow of New College, Oxford.