15 MARCH 2007
SANTA BARBARA – For evolution to produce complicated forms of life, offspring must resemble their parents.
New life forms emerge because the fittest offspring survive and reproduce, while less fit offspring tend to go extinct. Survivors pass on the beneficial traits they've inherited to subsequent generations. Over time, beneficial traits accumulate and more complex forms of life evolve.
If offspring did not resemble their parents, though, evolution would go nowhere.
Each subsequent generation would be just a new bunch of life forms, and the
battle for survival would start from scratch all over again.
Evolution therefore requires high-fidelity reproduction, along with an accurate genetic code so inherited traits can be accurately recorded. Today, the cellular machinery accomplishing that task is complex, consisting of dozens of enzymes and assorted RNA and protein molecules working together in harmony.
So where do all those molecules come from? Courtesy of the parent cells, of course. You inherit the machinery you need to produce the molecules that make inheritance possible.
If that sounds like a chicken and egg problem, you're catching on to the biggest problem in evolutionary biology: namely, how did it all get started in the first place?
Once you have a cellular machine capable of high-fidelity reproduction, evolution takes off, says Eugene Koonin, of the National Center for Biotechnology Information in Bethesda, Md. Beneficial mutations are preserved in offspring and natural selection does the rest. But how could complicated reproduction machinery evolve before natural selection was possible?
The standard answer is that current hereditary machinery, based on the famous double-stranded molecule DNA, was preceded by some more primitive system. Most likely, many experts say, DNA's chemical cousin RNA appeared first. RNA molecules store information and possess chemical capabilities that could make reproducing such information possible.
Serious
work on the details, though, has not yet shown how RNA could produce a
reproduction system faithful enough to generate the complexity that natural
selection requires, as Koonin explained in a recent talk at the Kavli
Institute for Theoretical Physics at the University of California, Santa
Barbara.
So perhaps, he says, the problem is too hard to solve with Earthbound biology. Instead it might require an explanation of cosmic magnitude. Koonin argues that the solution to the evolution chicken-egg riddle may be hidden deep in the history of the universe itself.
Photo from Wikipedia taken by Paul Smith for http://www.apepta.co.uk and kindly supplied by Martin Fox at http://www.elvis2k.co.uk
Current theories suggest that the visible universe originated 13.6 billion years ago when a tiny patch of nothingness suddenly puffed up into something like space as we know it. That original puffball then expanded into the vast cosmos that the Hubble Space Telescope likes to take pictures of today.
Plenty of evidence supports the idea of the initial puff-up, known as inflation. And if that puffing up process happened once, some experts believe, it probably happened again. And again and again, eternally. If so, there would be an infinite number of universes. Not all would be just like ours, but there would be as many just like ours as you'd like.
Now, infinity is creepy. In an infinite number of universes, anything that is possible (allowed by the laws of physics) will happen, an infinite number of times. Consequently, as Koonin points out in a recent paper, in some universes Elvis is still alive.
More important for evolution, though, in some universes the cellular machinery for high-fidelity reproduction would assemble itself just by chance. Sure, it's not very likely. But with an infinity of universes, it would certainly happen someplace. And wherever it happened, that's where life as we know it would then have evolved, producing the complex organisms (such as people) making that universe interesting, while most others would remain lifeless and boring.
True, in some universes, people would just pop into existence, because any possible arrangement of molecules will happen, somewhere. Any conceivable history can occur. In fact, the RNA World that some biologists believe in would also happen someplace. "All histories are real," Koonin said in his talk. "The question is, which one is ours? . . . What we are trying to figure out is the most likely history for our world."
At first glance, Koonin's ideas seem similar to those discussed by advocates of "intelligent design," who say God (or somebody) just made things the way they are, since it is too improbable for life to get going on its own. But Koonin's point is actually just the opposite. In a realm with an infinity of universes, nothing is too unlikely to happen. It doesn't matter how improbable something is, it will still happen with certainty.
"I believe this approach just closes the door to intelligent design," Koonin declared.
Still, Koonin's idea has potential flaws. For one thing, discovery of life elsewhere in the galaxy would demolish his argument -- spontaneous assembly of complex cellular machinery is too rare to happen more than once in the same universe.
F
or
that matter, further research may show how RNA actually could construct
the reproductive system that natural selection needs. And the multiple-universe
inflation idea, while compelling to some astronomers, has not really been
conclusively established yet, either.
Nevertheless, such ideas are worth pursuing, just to see where they go. In science, hard problems might need unusual, even fantastic, solutions. Wild ideas that go nowhere will eventually go extinct, anyway. But the wild ideas that survive could be the ancestors to the successful theories of future generations.
E-mail: tsiegfried@nasw.org
