Technology / Computers

If you want to find alien life-forms, hold off on booking that trip to the moons of Saturn. You may only need to catch a plane to East Lansing, Michigan.

The aliens of East Lansing are not made of carbon and water. They have no DNA. Billions of them are quietly colonizing a cluster of 200 computers in the basement of the Plant and Soil Sciences building at Michigan State University. To peer into their world, however, you have to walk a few blocks west on Wilson Road to the engineering department and visit the Digital Evolution Laboratory. Here you’ll find a crew of computer scientists, biologists, and even a philosopher or two gazing at computer monitors, watching the evolution of bizarre new life-forms.

These are digital organisms—strings of commands—akin to computer viruses. Each organism can produce tens of thousands of copies of itself within a matter of minutes. Unlike computer viruses, however, they are made up of digital bits that can mutate in much the same way DNA mutates. A software program called Avida allows researchers to track the birth, life, and death of generation after generation of the digital organisms by scanning columns of numbers that pour down a computer screen like waterfalls.

After more than a decade of development, Avida’s digital organisms are now getting close to fulfilling the definition of biological life. “More and more of the features that biologists have said were necessary for life we can check off,” says Robert Pennock, a philosopher at Michigan State and a member of the Avida team. “Does this, does that, does this. Metabolism? Maybe not quite yet, but getting pretty close.”

One thing the digital organisms do particularly well is evolve. “Avida is not a simulation of evolution; it is an instance of it,” Pennock says. “All the core parts of the Darwinian process are there. These things replicate, they mutate, they are competing with one another. The very process of natural selection is happening there. If that’s central to the definition of life, then these things count.”

It may seem strange to talk about a chunk of computer code in the same way you talk about a cherry tree or a dolphin. But the more biologists think about life, the more compelling the equation becomes. Computer programs and DNA are both sets of instructions. Computer programs tell a computer how to process information, while DNA instructs a cell how to assemble proteins.

The ultimate goal of the instructions in DNA is to make new organisms that contain the same genetic instructions. “You could consider a living organism as nothing more than an information channel, where it’s transmitting its genome to its offspring,” says Charles Ofria, director of the Digital Evolution Laboratory. “And the information stored in the channel is how to build a new channel.” So a computer program that contains instructions for making new copies of itself has taken a significant step toward life.

A cherry tree absorbs raw materials and turns them into useful things. In goes carbon dioxide, water, and nutrients. Out comes wood, cherries, and toxins to ward off insects. A computer program works the same way. Consider a program that adds two numbers. The numbers go in like carbon dioxide and water, and the sum comes out like a cherry tree.

In the late 1990s Ofria’s former adviser, physicist Chris Adami of Caltech, set out to create the conditions in which a computer program could evolve the ability to do addition. He created some primitive digital organisms and at regular intervals presented numbers to them. At first they could do nothing. But each time a digital organism replicated, there was a small chance that one of its command lines might mutate. On a rare occasion, these mutations allowed an organism to process one of the numbers in a simple way. An organism might acquire the ability simply to read a number, for example, and then produce an identical output.

Adami rewarded the digital organisms by speeding up the time it took them to reproduce. If an organism could read two numbers at once, he would speed up its reproduction even more. And if they could add the numbers, he would give them an even bigger reward.Within six months, Adami’s organisms were addition whizzes. “We were able to get them to evolve without fail,” he says. But when he stopped to look at exactly how the organisms were adding numbers, he was more surprised. “Some of the ways were obvious, but with others I’d say, ‘What the hell is happening?’ It seemed completely insane.”

On a trip to Michigan State, Adami met microbiologist Richard Lenski, who studies the evolution of bacteria. Adami later sent Lenski a copy of the Avida software so he could try it out for himself. On a Friday, Lenski loaded the program into his computer and began to create digital worlds. By Monday he was tempted to shut down his laboratory and dedicate himself to Avida. “It just had the smell of life,” says Lenski.

It also mirrored Lenski’s own research, launched in 1988, which is now the longest continuously running experiment in evolution. He began with a single bacterium—Escherichia coli—and used its offspring to found 12 separate colonies of bacteria that he nurtured on a meager diet of glucose, which creates a strong incentive for the evolution of new ways to survive. Over the past 17 years, the colonies have passed through 35,000 generations. In the process, they’ve become one of the clearest demonstrations that natural selection is real. All 12 colonies have evolved to the point at which the bacteria can replicate almost twice as fast as their ancestors. At the same time, the bacterial cells have gotten twice as big. Surprisingly, these changes didn’t unfold in a smooth, linear process. Instead, each colony evolved in sudden jerks, followed by hundreds of generations of little change, followed by more jerks.

Similar patterns occur in the evolution of digital organisms in Avida. So Lenski set up digital versions of his bacterial colonies and has been studying them ever since. He still marvels at the flexibility and speed of Avida, which not only allow him to alter experimental conditions with a few keystrokes but also to automatically record every mutation in every organism. “In an hour I can gather more information than we had been able to gather in years of working on bacteria,” Lenski says. “Avida just spits data at you.”

With this newfound power, the Avida team is putting Darwin to the test in a way that was previously unimaginable. Modern evolutionary biologists have a wealth of fossils to study, and they can compare the biochemistry and genes of living species. But they can’t look at every single generation and every single gene that separates a bird, for example, from its two-legged dinosaur ancestors. By contrast, Avida makes it possible to watch the random mutation and natural selection of digital organisms unfold over millions of generations. In the process, it is beginning to shed light on some of the biggest questions of evolution.