How evolution evolved
Posted: Friday, January 09, 2009 11:53 AM by Alan Boyle
Janet Iwasa / Harvard Med. School and Mass. Gen. Hospital
This cutaway view shows a model protocell about 100 nanometers in diameter. The
protocell's fatty acid membrane allows nutrients and DNA building blocks to enter
the cell and create copies of the cell's DNA. The new DNA strands remain inside.
Scientists suggest this is how the first living cells began to evolve eons ago.
|
Where did the theory of evolution come from? And where's it going? Essayists and scientists are rallying to answer such questions during the countdown to Charles Darwin's 200th birthday.
The folks who want to build up Darwin's legacy (and the folks who want to challenge it) are gearing up for Feb. 12 by reflecting on the past, present and future of evolutionary theory. Scientific American has devoted virtually an entire issue of the magazine to the topic already, and this week the journal Science made Darwin its cover boy.
Evolution's past
Among the journal's highlights is a review article by Peter J. Bowler, a historian from the Queen's University of Belfast who focuses on the roots of Darwin's theory. Some might argue that Darwinism was so much "in the air" 150 years ago that if Darwin hadn't come up with the idea, someone else would have figured it out. But that's not the way Bowler sees it.
To be sure, other biologists had worked out the main outlines of the theory of natural selection - that is, the idea that advantageous traits become more common in succeeding generations. One of the reasons why Darwin published "On the Origin of Species" when he did was because another biologist, Alfred Russel Wallace, was working on his own theory along similar lines.
Bowler maintains, however, that Darwin's formulation of the theory "was both original and disturbing."
"It was not just that the idea of natural selection challenged the belief that the world was designed by a wise and benevolent God," Bowler writes. "There was a wider element of teleology or goal-directedness almost universally accepted at the time."
Darwin would have scoffed at the idea that the evolutionary process was designed to go in any particular direction, other than pointing toward survival in "the struggle for existence."
Some critics have complained that evolution the way Darwin saw it was a cold-hearted process, and laid the groundwork for the horrors of Nazism and Stalinism. (That theme comes through loud and clear in last year's anti-Darwin documentary, "Expelled.") In response, Bowler insists that "Darwinism was not 'responsible' for social Darwinism or eugenics in any simple way," but he acknowledges that some of the more disturbing aspects of his theory were exploited by later generations.
"We may well feel uncomfortable with those aspects of his theory today, especially in light of their subsequent applications to human affairs," Bowler writes. "But if we accept science's power to upset the traditional foundations of how we think about the world, we should also accept its potential to interact with moral values."
That's food for thought, well worth chewing over in the comment section below.
Evolution's present and future
Another essay in the journal, written by award-winning author Carl Zimmer, takes a closer look at the ultimate question that Darwin barely addressed in his writings: How did life itself arise? The full essay is available on Science's Web site as well as on CarlZimmer.com.
Zimmer touches upon several paths now being explored to address that question, including a reworking of the classic Miller-Urey experiment that changes the recipe for a "primordial soup" that could give rise to life's building blocks. The new brew is a better reflection of what scientists now think Earth's early atmosphere was like (with lots of carbon dioxide and a dash of nitrogen), and adds some extra chemicals that would allow amino acids to form when zapped by lightning.
Other lines of research look at the potential for simple molecules to bootstrap themselves into more complex, self-replicating molecules - eventually leading to life as we know it. For years, scientists have speculated that biology began with a molecular genetic system that no longer exists in nature, worked its way up to an "RNA world," and at last gave rise to the DNA-based system we see today.
Chemists are slowly closing in on what could be a plausible explanation of the process, Zimmer reports. "We've got the molecules in our sights," the University of Manchester's John Sutherland told him.
One of the most intriguing bits of research was published this week on Science's Web site: Biologists at the Scripps Research Institute report that they built a set of self-replicating RNA enzymes that could serve as "an experimental model of a genetic system." The chemical reactions gave rise to the game of life, without biology.
Wired Science's Alexis Madrigal quotes one of the paper's co-authors, Gerald Joyce, as saying the experiment showed how evolution can take hold in the RNA world. "All the original replicators went extinct and it was the new recombinants that took over," Joyce said. "There wasn't one winner. There was a whole cloud of winners, but there were three mutants that arose that pretty much dominated the population."
Still other researchers are working on the artificial cells to contain artificial life. The aim here isn't to create Frankenmicrobes: A team from Penn State explained last year that studying artificial cells could help scientists develop more effective pharmaceuticals for natural-born cells. Such experiments could also shed light on how the first protocells took shape on the early Earth.
Animation by Janet Iwasa shows how a protocell can form from fatty acids.
The latest revelations demonstrate how evolutionary theory - and practice - is still evolving today. There's also a spurt of differentiation in how the field is being covered: Just this week, Science launched its Origins blog to keep track of all the Darwin doings, and the bicentennial will be a leading theme during next month's annual meeting of the American Association for the Advancement of Science.
Here are a few more resources on evolutionary biology and the Darwin bicentennial:
