for National Geographic News
They don't sting or bite. They don't cause diarrhea or headaches. They don't even exist in a tangible form. But "digital organisms"— special programs that reproduce, mutate, and adapt —can thrive inside computers, and they are teaching scientists several lifetimes worth of information about evolution.
These artificial "bugs" show that complex functions that are the digital equivalent to something like human eyesight can evolve from the simplest of functions via a long and winding road of gradual mutation, according to a team consisting of a biologist, a computer scientist, a philosopher, and a physicist.
"From comparative studies of living organisms, as well as the fossil record, it's long been clear that new functions don't just suddenly appear out of nowhere, but rather organisms have evolved new structures and functions out of old ones, by tweaking bits and pieces here and there," said Richard Lenski, a biologist at Michigan State University in East Lansing.
Lenski and his colleagues Charles Ofria and Robert Pennock at Michigan State University and Christoph Adami at the California Institute of Technology in Pasadena report on their research with the digital organisms in the May 8 issue of Nature.
Thomas Ray, a biologist at the University of Oklahoma in Norman, who designed digital organisms in the early 1990s, said the study "doesn't surprise evolutionary biologists, but rather is a completely clear and detailed analysis of what we believe."
Digital Evolution
Ever since Charles Darwin theorized about evolution in the 19th century, biologists have believed that complex features such as eyesight must have arisen through many steps and that some of the intermediate steps must have served different functions from what is observed today.
But while functions change, biologists have assumed that each step along the path to a complex new function is a step up—an improvement—in terms of producing an organism that is better adapted to its environment.
The problem is that evolution in the natural world is a slow process, making it difficult to watch the process play itself out and thus test these assumptions, said Lenski.
To speed things up, he and his colleagues placed digital organisms in a computer environment that was programmed to allow the organisms to replicate, mutate, and compete.
"We created a world in which these things are possible and the right organisms can take advantage of it," said Adami, a physicist, who designed the simulated environment to allow the evolutionary process to work as it does in the natural world.
And since the process is saved on a computer, the scientists can analyze the sequence of events that leads to the ability to perform a complex new function.
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