But I digress. Back to genomes. A genome is a digital computer program of immense complexity. The slightest mistake would alter the pattern, dose or sequence of expression of its 20,000 genes (in human beings), or affect the interaction of its hundreds of thousands of control sequences that switch genes on and off, and result in disastrous deformity or a collapse into illness. In most of us, for an incredible eight or nine decades, the computer program runs smoothly with barely a glitch.
Consider what must happen every second in your body to keep the show on the road. You have maybe ten trillion cells, not counting the bacteria that make up a large part of your body. Each of those cells is at any one time transcribing several thousand genes, a procedure that involves several hundred proteins coming together in a specific way and catalysing tens of chemical reactions for each of millions of base pairs. Each of those transcripts generates a protein molecule, thousands of amino acids long, which it does by entering a ribosome, a machine with tens of moving parts, capable of catalysing a flurry of chemical reactions. The proteins themselves then fan out within and without cells to speed reactions, transport goods, transmit signals and prop up structures. Millions of trillions of these immensely complicated events are occurring every second in your body to keep you alive, very few of which go wrong. It’s like the world economy in miniature, only even more complex.
It is hard to shake the illusion that for such a computer to run such a program, there must be a programmer. Geneticists in the early days of the Human Genome Project would talk of ‘master genes’ that commanded subordinate sequences. Yet no such master gene exists, let alone an intelligent programmer. The entire thing not only emerged piece by piece through evolution, but runs in a democratic fashion too. Each gene plays its little role; no gene comprehends the whole plan. Yet from this multitude of precise interactions results a spontaneous design of unmatched complexity and order. There was never a better illustration of the validity of the Enlightenment dream – that order can emerge where nobody is in charge. The genome, now sequenced, stands as emphatic evidence that there can be order and complexity without any management.
On whose behalf?
Let’s assume for the sake of argument that I have persuaded you that evolution is not directed from above, but is a self-organising process that produces what Daniel Dennett calls ‘free-floating rationales’ for things. That is to say, for example, a baby cuckoo pushes the eggs of its host from the nest in order that it can monopolise its foster parents’ efforts to feed it, but nowhere has that rationale ever existed as a thought either in the mind of the cuckoo or in the mind of a cuckoo’s designer. It exists now in your mind and mine, but only after the fact. Bodies and behaviours teem with apparently purposeful function that was never foreseen or planned. You will surely agree that this model can apply within the human genome, too; your blood-clotting genes are there to make blood-clotting proteins, the better to clot blood at a wound; but that functional design does not imply an intelligent designer who foresaw the need for blood clotting.
I’m now going to tell you that you have not gone far enough. God is not the only skyhook. Even the most atheistic scientist, confronted with facts about the genome, is tempted into command-and-control thinking. Here’s one, right away: the idea that genes are recipes patiently waiting to be used by the cook that is the body. The collective needs of the whole organism are what the genes are there to serve, and they are willing slaves. You find this assumption behind almost any description of genetics – including ones by me – yet it is misleading. For it is just as truthful to turn the image upside down. The body is the plaything and battleground of genes at least as much as it is their purpose. Whenever somebody asks what a certain gene is for, they automatically assume that the question relates to the needs of the body: what is it for, in terms of the body’s needs? But there are plenty of times when the answer to that question is ‘The gene itself.’
The scientist who first saw this is Richard Dawkins. Long before he became well known for his atheism, Dawkins was famous for the ideas set out in his book The Selfish Gene. ‘We are survival machines – robot vehicles blindly programmed to preserve the selfish molecules known as genes,’ he wrote. ‘This is a truth that still fills me with astonishment.’ He was saying that the only way to understand organisms was to see them as mortal and temporary vehicles used to perpetuate effectively immortal digital sequences written in DNA. A male deer risks its life in a battle with another stag, or a female deer exhausts her reserves of calcium producing milk for her young, not to help its own body’s survival but to pass the genes to the next generation. Far from preaching selfish behaviour, therefore, this theory explains why we are often altruistic: it is the selfishness of the genes that enables individuals to be selfless. A bee suicidally stinging an animal that threatens the hive is dying for its country (or hive) so that its genes may survive – only in this case the genes are passed on indirectly, through the stinger’s mother, the queen. It makes more sense to see the body as serving the needs of the genes than vice versa. Bottom–up.
One paragraph of Dawkins’s book, little noticed at the time, deserves special attention. It has proved to be the founding text of an extremely important theory. He wrote:
Sex is not the only apparent paradox that becomes less puzzling the moment we learn to think in selfish gene terms. For instance, it appears that the amount of DNA in organisms is more than is strictly necessary for building them: a large fraction of the DNA is never translated into protein. From the point of view of the individual this seems paradoxical. If the ‘purpose’ of DNA is to supervise the building of bodies it is surprising to find a large quantity of DNA which does no such thing. Biologists are racking their brains trying to think what useful task this apparently surplus DNA is doing. From the point of view of the selfish genes themselves, there is no paradox. The true ‘purpose’ of DNA is to survive, no more and no less. The simplest way to explain the surplus DNA is to suppose that it is a parasite, or at best a harmless but useless passenger, hitching a ride in the survival machines created by the other DNA.
One of the people who read that paragraph and began thinking about it was Leslie Orgel, a chemist at the Salk Institute in California. He mentioned it to Francis Crick, who mentioned it in an article about the new and surprising discovery of ‘split genes’ – the fact that most animal and plant genes contain long sequences of DNA called ‘introns’ that are discarded after transcription. Crick and Orgel then wrote a paper expanding on Dawkins’s selfish DNA explanation for all the extra DNA. So, at the same time, did the Canadian molecular biologists Ford Doolittle and Carmen Sapienza. ‘Sequences whose only “function” is self-preservation will inevitably arise and be maintained,’ wrote the latter. The two papers were published simultaneously in 1980.
It turns out that Dawkins was right. What would his theory predict? That the spare DNA would have features that made it good at getting itself duplicated and re-inserted into chromosomes. Bingo. The commonest gene in the human genome is the recipe for reverse transcriptase, an enzyme that the human body has little or no need for, and whose main function is usually to help the spread of retroviruses. Yet there are more copies and half-copies of this gene than of all other human genes combined. Why? Because reverse transcriptase is a key part of any DNA sequence that can copy itself and distribute the copies around the genome. It’s a sign of a digital parasite. Most of the copies are inert these days, and some are even put to good use, helping to regulate real genes or bind proteins. But they are there because they are good at being there.
The skyhook here is a sort of cousin of Locke’s ‘mind-first’ thinking: the assumption that the human good is the only good pursued within our bodies. The alternative view, penetratingly articulated by Dawkins, takes the perspective of the gene itself: how DNA would behave if it could. Close to half of the human genome consists of so-called transposable elements designed to use reverse transcriptase. Some of the commonest are known by names like LINEs (17 per cent of the genome), SINEs (11 per cent) and LTR retrotransposons (8 per cent). Actual genes, by contrast, fill just 2 per cent of the genome. These