TCS Daily


The Blind Bookmaker

By Johnjoe McFadden - September 23, 2002 12:00 AM

Religion has been in retreat since Galileo's day. Copernicus cast the Earth from the centre of the universe; Newton captured the heavens in his laws of motion. The devout pinned their hopes on a special place for man but Darwin revealed us as monkeys that had climbed down from the trees. What is left for religion?

Just one big mystery: the origin of life. No entirely satisfactory scientific explanation has fully accounted for its emergence. Creationists pin their faith on life's improbability, which they see as evidence for the hand of God. But I believe that quantum mechanics unlocks this final mystery.

In the Garden

The early Earth was no Eden. Bombarded by comets and showered with volcanic ash, it wasn't until 3.8 billion years ago that conditions settled sufficiently for a stable water ocean to form - a prerequisite for life. Yet by that time there is isotopic evidence of photosynthesis in ancient rock. Fossil bacteria can be found in the most ancient intact rocks, which date to about 3.5 billion years ago. Life may have been improbable, but it was quick.

How did the chaotic chemistry in those ancient seas yield life? The problem is the enormous difference in complexity between living organisms and the products of the inorganic chemistry.

The genome of one of the simplest creatures - a bacterium called mycoplasma - has recently been sequenced and found to encode more than 400 different genes. Each gene is made up of about 1,000 genetic instructions. Making just one of these genetic units, a 'nucleotide base', is extraordinarily difficult.

The chemist, Cairns-Smith, estimated that it takes 140 steps to synthesize a nucleotide base from plausible 'primordial soup' precursors. The chances of each of these random steps occurring in the right sequence to yield even a single RNA base on the early Earth are remote. The chances of them coming together to yield a gene are infinitesimally small.

At this point, creationists often wheel in a band of monkeys with typewriters to drive home their point. The question is asked: how long would it take a simian typist banging wildly on the keys to type out the entire text of Hamlet? The answer is forever.

In fact if we had a cosmic army of monkeys, one for every single electron in the universe, and they had all been typing merrily away ever since the Big Bang, then even they would not have had sufficient time to type even Act One. Similarly, so creationists argue, random forces could not have generated life; only God makes life.

Simple Solutions

Most scientists believe instead that something much simpler must have preceded the first living cells. Although there is an obvious weakness in this argument (if life was simpler then, why is it so complex today?), most origin-of-life researchers opt for this solution. The standard theory is that before cells there were self-replicating molecules.

David Lee of California's Scripps Research Institute has recently constructed a small protein made up of 32 amino acids that can stitch two halves of itself together to make a copy (albeit under very un-primordial conditions). If a similar protein was made in the early seas then the Darwinian formula of 'replicate, vary, let the strong survive and the weak die' could have kick started evolution, leading eventually to the first cells and life as we know it.

Could Lee's self-replicator - or something like it - have been made in the primordial seas? Proteins are polymers of amino acids. In the 1950s Stanley Miller and Harold Urey startled the scientific world by showing how easy it was to make amino acids in a laboratory simulation. But Miller and Urey's experiments were actually a bit of a fix. They incubated their primordial soups in a hydrogen-rich atmosphere that scientists no longer believe existed on the early Earth. Without the hydrogen, the soups yield very few amino acids.

But perhaps, in some primordial pond, conditions were just right to make amino acids. Surely all that was then needed was to cook the organic soup for several million years to form more complex proteins like Lee's? Unfortunately, no amount of cooking yields complex proteins. As any chef knows, lengthy cooking destroys, rather than makes, complex polymers like proteins.

A further obstacle is the 'handedness' of life. Most amino acids come in left and right-handed forms but living cells are not ambidextrous; they can only handle one of the two forms. The laboratory-based primordial soups yield both left- and righted-handed amino acids and these mixtures do not polymerise to form proteins.

Even if all these problems were overcome and polymeric proteins were formed in the soup, how likely is it that Lee's protein would be among them? The final problem is one of numbers. Since there are 20 different amino acids that go into protein, Lee's replicator is just one amongst trillions.

To have a reasonable chance of making just one molecule of the Lee replicator, the primordial seas would have had to generate a mass of protein equivalent five thousand times the total biomass in all the world's tropical forests today. No primordial sea was that big.

Life's Origin

So how did life originate? I believe quantum mechanics provides the missing ingredient. Quantum mechanics is the strangest of sciences, yet it is built upon attempts to understand very simple experiments. One is known as the two-slit experiment. Shine a light through two holes and you will generate a series of light and dark bands on a screen known as an interference pattern. The bands are generated by the waves of light emerging from both slits recombining either with their peaks and troughs in step (light bands) or out of step (dark bands). Waves are spread out, allowing them to pass through two points (two holes) simultaneously and so generate interference.

Waves make waves but atoms and molecules are particles that have discrete sizes and locations. We do not expect them to be wavy. Yet in the two-slit experiment, they generate the same kind of interference patterns as you get with light. Somehow, these single particles are able to travel trough distinct points in space simultaneously, just like a wave.

Nobody really understands how they do it. The standard 'Copenhagen' interpretation claims that the world isn't entirely real (allowing an 'unreal' atom to travel through both hole) until a 'measurement' is made. Another proposal has signals travel backwards and forward in time to connect every particle in the universe, giving rise to the interference effects.

One of the most bizarre interpretations, but one that has the backing of Nobel prize-winning physicists, is to take the two-slit experiment at its face value. It looks like a single particle travels through both holes, so maybe it does. But the two holes are in parallel universes. In this 'multiverse' interpretation, every possible event that happens in this universe, a host of alternative events happen in other universes. Everything possible happens in a 'multiverse' of parallel universes.

The multiverse interpretation may sound preposterous, but it is at least simpler to visualise than its rivals. So let us look again at the early Earth, but within the multiverse. We are back in the primordial soup. The same reactions as before, but now every possible chemical reaction is taking place within the multiverse. The chances of the components coming together to form a molecular self-replicator - like Lee's peptide or even a living cell - are still extraordinarily low.

But - and it is a crucial but - that probability is not zero. So long as there is some possible path for electrons, protons and atoms to take that leads to a self-replicator, then that path will be taken in one of the trillions of possible universes that make up the multiverse.

So self-replication and life are bound to emerge - though in perhaps just one of a multitude of universes. But which universe do we inhabit? It must be the one that generated life. Our presence here guarantees that we live in the universe that struck lucky.

So life is a product not just of our universe, but of a multitude of parallel universes. But if you still don't like the multiverse, you can reframe this scenario in the interpretation of your choosing. In the Copenhagen interpretation, the early steps towards life would have taken place within a kind of probability cloud until a measurement was made. Life would have made that measurement.
The creationists can dismiss their bands of typing monkeys. Quantum mechanics guarantees life's emergence.

Johnjoe McFadden is professor of molecular genetics at the University of Surrey in southeast England, is the author of "Quantum Evolution" (Norton).
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