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Wednesday, June 13, 2007
LIFE'S ORIGINS IN THE SOUP
Religion's cute, but creation chemistry is complex
By ROWAN HOOPER
The ancient Chinese believed the universe began inside a cosmic egg. In Japanese mythology, two gods, Izanagi and Izanami, stirred the oceans with a giant spear, forming the islands of Japan and, eventually, its people. There are countless more creation myths. Every culture has them. But I like to think that the Buddha understood the absurdity of speculating about the origin of life, when he reportedly said the following:
"Conjecture about the origin of the world is an unconjecturable that is not to be conjectured about, that would bring madness and vexation to anyone who conjectured about it."
I think he's right, because conjecture based on mythology can only bring madness, or delusion. He was a wise man to see that.
Luckily however, long after the Buddha died, a system of learning about the world came along — a system known as science, that isn't based on conjecture, but on collecting and verifying information. Using this system, scientists do indeed make conjectures about origins.
Another wise man, Charles Darwin, was one of the first in the modern world to do that. Life, he wrote in 1871, may have begun in a "warm little pond, with all sorts of ammonia and phosphoric salts, lights, heat, electricity, etc. present, [so] that a protein compound was chemically formed ready to undergo still more complex changes."
Since then, Darwin's suggestion has been much refined.
Before life arose we know there must have been some chemical mechanisms for generating energy — that is, some simple metabolic process must have been available to convert food into energy. There also must have been some sort of genetic system for telling the metabolic processes how to copy themselves. Understanding these processes is one thing, but the problem remains: What preceded these pre-life steps?
Ken Dill, a pharmaceutical chemist at the University of California, San Francisco, has an idea that this column is only too happy to report, seeing as it is based on natural selection — except that Dill's idea has natural selection operating on a nanoscale. Enzymes can cooperate and compete with each other in simple ways and, Dill says, successful ones become stable, or "locked in."
It's analogous, Dill says, to the way memories form, and ants forage. In the brain, neurons fire at different rates and connections form between different points. Neural pathways are laid down and a wiring pattern gets set into the architecture of the brain. When ants forage, they wander about randomly. When they discover food, they lay down a trail that other ants can follow. The ants that follow then lay down their own "food this way" chemical, and the trail grows stronger and clearer.
Dill, working with colleague Justin Bradford, built a mathematical model to investigate how this process could work in the "primordial soup" of simple chemicals that Darwin envisaged.
Natural selection works by picking out the traits that are best suited to the environment, and Dill and Bradford used the same principle in their model. Instead of genes and traits being selected — as happens in "normal" natural selection — in the model, chemicals interact.
So what happens?
In the "soup" of the model are two types of enzymes — chemicals that catalyze reactions. Enzyme A catalyzes reaction 1, and enzyme B catalyzes reaction 2. The researchers assume that A produces a chemical that B uses. A will naturally "seek out" enzyme B because it "wants" that chemical. The result is that the two enzymes will come into proximity, and form a complex, AB.
I'm using "seek out" and "wants" as shorthand. The enzymes don't make conscious decisions, of course. But if one makes a chemical that the other uses, it follows from basic chemistry that more complex molecules will form. It doesn't require any consciousness — nor even life.
Dill is excited about what this means.
"A major question about life's origins is how chemicals, which have no self-interest, became 'biological' — driven to evolve by natural selection," he says. "This simple model shows a plausible route to this type of complexity."
Complexity is a factor that puzzled biologists for centuries before Darwin solved the problem of how it arises.
The puzzle is what drove people to creation myths such as the Chinese cosmic egg, or the various myths in Judaism, Christianity or Islam that describe a supreme being who created the universe, the world and everything in it? Some religious people falsely think they can use science to support their myths, most notoriously at the moment, the creationists of the so-called Intelligent Design movement.
Darwin showed how life could evolve complexity through a simple, unconscious process — natural selection — that leads to things such as eyes and hands that look like they've been designed for a purpose but don't actually require any direction. Dill and Bradford, writing in the Proceedings of the National Academy of Sciences, show how complex molecules could also arise without direction.
"This simple model shows a plausible route to this type of complexity," said Dill.
What's exciting about the work is that it can be tested. An experiment can be set up that tests to see if real catalysts, such as A and B in the model, do form complexes. Cosmic eggs and Abrahamic stories of God creating the heavens and the earth are cute enough, but they're only stories. How much more thrilling to think that we may one day be able to explain how life began.
The second volume of Natural Selections columns translated into Japanese is published by Shinchosha, priced 1,500 yen. The title is "Hito wa ima mo shinka shiteru (The Evolving Human: How new biology explains your journey through life)."
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