Bill Bryson - A short history of nearly everything

Proteins, in short, are complex entities. Hemoglobin is only 146 amino acids long, a runt by protein standards, yet even it offers 10 190possible amino acid combinations, which is why it took the Cambridge University chemist Max Perutz twenty-three years-a career, more or less-to unravel it. For random events to produce even a single protein would seem a stunning improbability-like a whirlwind spinning through a junkyard and leaving behind a fully assembled jumbo jet, in the colorful simile of the astronomer Fred Hoyle.

Yet we are talking about several hundred thousand types of protein, perhaps a million, each unique and each, as far as we know, vital to the maintenance of a sound and happy you. And it goes on from there. A protein to be of use must not only assemble amino acids in the right sequence, but then must engage in a kind of chemical origami and fold itself into a very specific shape. Even having achieved this structural complexity, a protein is no good to you if it can’t reproduce itself, and proteins can’t. For this you need DNA. DNA is a whiz at replicating-it can make a copy of itself in seconds-but can do virtually nothing else. So we have a paradoxical situation. Proteins can’t exist without DNA, and DNA has no purpose without proteins. Are we to assume then that they arose simultaneously with the purpose of supporting each other? If so: wow.

And there is more still. DNA, proteins, and the other components of life couldn’t prosper without some sort of membrane to contain them. No atom or molecule has ever achieved life independently. Pluck any atom from your body, and it is no more alive than is a grain of sand. It is only when they come together within the nurturing refuge of a cell that these diverse materials can take part in the amazing dance that we call life. Without the cell, they are nothing more than interesting chemicals. But without the chemicals, the cell has no purpose. As the physicist Paul Davies puts it, “If everything needs everything else, how did the community of molecules ever arise in the first place?” It is rather as if all the ingredients in your kitchen somehow got together and baked themselves into a cake-but a cake that could moreover divide when necessary to produce more cakes. It is little wonder that we call it the miracle of life. It is also little wonder that we have barely begun to understand it.

So what accounts for all this wondrous complexity? Well, one possibility is that perhaps it isn’t quite-not quite-so wondrous as at first it seems. Take those amazingly improbable proteins. The wonder we see in their assembly comes in assuming that they arrived on the scene fully formed. But what if the protein chains didn’t assemble all at once? What if, in the great slot machine of creation, some of the wheels could be held, as a gambler might hold a number of promising cherries? What if, in other words, proteins didn’t suddenly burst into being, but evolved .

Imagine if you took all the components that make up a human being-carbon, hydrogen, oxygen, and so on-and put them in a container with some water, gave it a vigorous stir, and out stepped a completed person. That would be amazing. Well, that’s essentially what Hoyle and others (including many ardent creationists) argue when they suggest that proteins spontaneously formed all at once. They didn’t-they can’t have. As Richard Dawkins argues in The Blind Watchmaker , there must have been some kind of cumulative selection process that allowed amino acids to assemble in chunks. Perhaps two or three amino acids linked up for some simple purpose and then after a time bumped into some other similar small cluster and in so doing “discovered” some additional improvement.

Chemical reactions of the sort associated with life are actually something of a commonplace. It may be beyond us to cook them up in a lab, à la Stanley Miller and Harold Urey, but the universe does it readily enough. Lots of molecules in nature get together to form long chains called polymers. Sugars constantly assemble to form starches. Crystals can do a number of lifelike things-replicate, respond to environmental stimuli, take on a patterned complexity. They’ve never achieved life itself, of course, but they demonstrate repeatedly that complexity is a natural, spontaneous, entirely commonplace event. There may or may not be a great deal of life in the universe at large, but there is no shortage of ordered self-assembly, in everything from the transfixing symmetry of snowflakes to the comely rings of Saturn.

So powerful is this natural impulse to assemble that many scientists now believe that life may be more inevitable than we think-that it is, in the words of the Belgian biochemist and Nobel laureate Christian de Duve, “an obligatory manifestation of matter, bound to arise wherever conditions are appropriate.” De Duve thought it likely that such conditions would be encountered perhaps a million times in every galaxy.

Certainly there is nothing terribly exotic in the chemicals that animate us. If you wished to create another living object, whether a goldfish or a head of lettuce or a human being, you would need really only four principal elements, carbon, hydrogen, oxygen, and nitrogen, plus small amounts of a few others, principally sulfur, phosphorus, calcium, and iron. Put these together in three dozen or so combinations to form some sugars, acids, and other basic compounds and you can build anything that lives. As Dawkins notes: “There is nothing special about the substances from which living things are made. Living things are collections of molecules, like everything else.”

The bottom line is that life is amazing and gratifying, perhaps even miraculous, but hardly impossible-as we repeatedly attest with our own modest existences. To be sure, many of the details of life’s beginnings remain pretty imponderable. Every scenario you have ever read concerning the conditions necessary for life involves water-from the “warm little pond” where Darwin supposed life began to the bubbling sea vents that are now the most popular candidates for life’s beginnings-but all this overlooks the fact that to turn monomers into polymers (which is to say, to begin to create proteins) involves what is known to biology as “dehydration linkages.” As one leading biology text puts it, with perhaps just a tiny hint of discomfort, “Researchers agree that such reactions would not have been energetically favorable in the primitive sea, or indeed in any aqueous medium, because of the mass action law.” It is a little like putting sugar in a glass of water and having it become a cube. It shouldn’t happen, but somehow in nature it does. The actual chemistry of all this is a little arcane for our purposes here, but it is enough to know that if you make monomers wet they don’t turn into polymers-except when creating life on Earth. How and why it happens then and not otherwise is one of biology’s great unanswered questions.

One of the biggest surprises in the earth sciences in recent decades was the discovery of just how early in Earth’s history life arose. Well into the 1950s, it was thought that life was less than 600 million years old. By the 1970s, a few adventurous souls felt that maybe it went back 2.5 billion years. But the present date of 3.85 billion years is stunningly early. Earth’s surface didn’t become solid until about 3.9 billion years ago.

“We can only infer from this rapidity that it is not ‘difficult’ for life of bacterial grade to evolve on planets with appropriate conditions,” Stephen Jay Gould observed in the New York Times in 1996. Or as he put it elsewhere, it is hard to avoid the conclusion that “life, arising as soon as it could, was chemically destined to be.”

Life emerged so swiftly, in fact, that some authorities think it must have had help-perhaps a good deal of help. The idea that earthly life might have arrived from space has a surprisingly long and even occasionally distinguished history. The great Lord Kelvin himself raised the possibility as long ago as 1871 at a meeting of the British Association for the Advancement of Science when he suggested that “the germs of life might have been brought to the earth by some meteorite.” But it remained little more than a fringe notion until one Sunday in September 1969 when tens of thousands of Australians were startled by a series of sonic booms and the sight of a fireball streaking from east to west across the sky. The fireball made a strange crackling sound as it passed and left behind a smell that some likened to methylated spirits and others described as just awful.