The evolutionary path from simple microbe to complex forms, on Earth or anywhere in the universe, is long, gradual and very Darwinian, according to a new experiment conducted with an "alien form of life" in a virtual petri dish.
Researchers prodded and annoyed life-like digital entities over more than 15,000 generations to learn that evolution among simple creatures is in fact based on the Darwinian notion of survival of the fittest and that the progress is plodding.
"The little things, they definitely count," says Richard Lenski, a Michigan State University evolutionary biologist who worked with a team of scientists from diverse backgrounds in creating and fostering artificial life inside a computer.
Basic disagreements
Scientists do not know how life on Earth evolved from simple organisms, which reigned for about 2.2 billion years, to more complex forms like flowering plants and galloping animals. Further, though most biologists agree evolution among higher life forms is Darwinian, they don't understand how it takes place.
Darwin looked at more than just how one species might become another. He also suggested the modern eye, for example, could not just have appeared, but must have evolved through many random mutations and the natural selection of those that proved beneficial. No one has proved that.
Among the biggest questions today among evolutionary theorists -- and this is a hotly debated one -- is how complex genes ever came to be. Genes are the basic units of information that define a creature and allow it to survive, adapt and procreate.
While simple observation might suggest that you are more complex than a microbe, experts don't even agree on a general definition of complexity. Also controversial is whether complexity actually increases with evolution.
Research with digital organisms assumes evolution does beget complexity, because the mutations inherent in species change give rise to more genes packing more information about a critter and its environment.
The ALife, as Lenski and his colleagues call their software creations, advance from simple organisms that could not perform any logic functions to complex organisms with great logical prowess. Their evolution was gradual, building on mutated abilities to perform simple functions.
The research was supported by the National Science Foundation and will be detailed in the May 8 issue of the journal Nature.
Bad is good
"Our work allowed us to see how the most complex functions are built up from simpler and simpler functions," Lenski said. "We also saw that some mutations looked like bad events when they happened, but turned out to be really important for the evolution of the population over a long period of time."
Lenski's team included philosopher Robert Pennock and computer scientist Charles Ofria, both from Michigan State, and Christoph Adami, a computation and neural systems researcher at Caltech and NASA's Jet Propulsion Laboratory.
Each digital organism is essentially a little computer program turned loose in the playground of life and rewarded for its ability to do math. An organism that makes successful computations is allowed to replicate, thereby gaining more computer time that can be used to achieve greater success.
"In a sense it's an alien form of life that we use in experiments to study evolution," Adami told SPACE.com, stressing that once the virtual world was set up, it ran just like a typical biological experiment. He called it a " bona fide life form" that has "nothing to do with any life form on Earth."
On any planet
Adami, who specializes in artificial-life research, said the premise of the study is that evolution is universal. "We think evolution should happen the same here as on any other planet," he said. That presumes there is life elsewhere, widely expected as a given by many leading scientists but not yet born out by any observational evidence.
Adami explained that the digital organisms evolved genes that develop computational skills, just as biological organisms develop genes that exploit energy-rich chemicals.
Importantly, the experiment found that complex logical ability never evolves unless simpler abilities -- foundational mutations -- are rewarded.
The virtual organisms are asexual. They reproduce by "binary fission." More research is needed to understand what role
plays in a Darwinian world, the scientists say. In the Nature paper, the researchers write that "sex might accelerate the evolution of complex features by combining functions that independently evolved in different lineages. On the other hand, asexuality permits beneficial combinations of mutations to spread even when they are individually deleterious, as sometimes occurred in our experiments."
An overseer program, called avida, serves as Nature and randomly infuses organisms with bugs, to simulate mutations that occur in the real world. In less than a hundred generations, the offspring can develop computer code -- their blueprints for thriving and reproducing -- that bear little or no resemblance to what Adami and his colleagues gave them to begin with.
Total control
Because the whole setup is virtual and controlled to some extent by its human creators, generations upon generations can be spawned in a relative eyeblink. The approach is known as evolutionary design.
Unlike a biological experiment, every nuance of the Avida world can be precisely logged. Also, biologists are vexed by many missing links in the long history of life on Earth.
"The cool thing is that we can trace the line of descent," Lenski said. "Out of a big population of organisms you can work back to see the pivotal mutations that really mattered during the evolutionary history of the population."
Not all biologists accept ALife as true life forms. Benton Clark, an astrobiologist at the University of Colorado and Lockheed Martin, says the term "digital organisms" might be confusing or misleading. He prefers to call them "artificial, simulated organisms" or "virtual organisms."
Whatever they're called, the critters designed by the Avida system seem to have shown real-world scientists the limits of their own evolution.
"Evolutionary design can often solve problems better than we can using our own intelligence," said Pennock, the philosopher.
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