"If a new, unforeseen task emerges, a robot might construct a new, more suitable robot from scratch, and then the new robot will dismantle the old robot," he said. "These kinds of scenarios, where machines sustain themselves and adapt by consuming and recycling components, get a little closer to the way biology works."
The prevailing view holds that self-replication is an ability that organisms or objects either have in full or lack entirely. But Lipson's team theorizes that self-replication isn't a yes-or-no proposition, but exists at varying degrees.
The researchers present their new robot as an example of this theory.
The team says the extent to which something is self-replicating depends on many factors. For example, mineral crystals build exact replicas of themselves, but only in a solution. By contrast, rabbits reproduce themselves less accurately than crystals do but are less dependent on a specific environment.
Through understanding the principles of self-replication in nature, the team aims to make robots that are more robust and adaptive.
"We are interested in making a practical robot that can self-reproduce but also do something useful," Lipson said. "We are also interested in making these machines at microscale."
Nanotechnology involves the precise manipulation of atoms and molecules to create structures around the scale of one billionth of a meter. Proponents say this fast-expanding field, seen by some as the next industrial revolution, could potentially change the way almost everything is manufactured, from medicines to automobiles.
More advanced nanotechnology could see the creation of nanomachines. For instance, so-called nanobots could be programmed to attack and reconstruct the cells of cancer patients or perform surgeries a thousand times more precise than currently possible.
A crucial objective of nanotechnology is to make products inexpensively, says Ralph Merckle, a professor at the Georgia Institute of Technology's College of Computing in Atlanta.
"While the ability to make a few very small, very precise molecular machines very expensively would clearly be a major scientific achievement, it would not fundamentally change how we make most products," he said.
What's needed, he says, are huge numbers of robots working together at a molecular scale. Self-replication is seen as a way of achieving this, using nanobots that can create copies of themselves to form vast numbers of microscopic assemblers.
Such a scenario has sparked fears among environmentalists and others who have warned of an apocalyptic "gray goo" event, with self-replicating nanobots possibly running amok and consuming the planet in a matter of days.
Indeed, researchers at Rice University in Texas recently reported that nanosize buckyballs (soccer ball-shaped carbon molecules) are water soluble and can interfere with the respiration of soil microbes.
And last year scientists at Southern Methodist University, also in Texas, reported that those same molecules, often used in nanotechnology, cause brain damage in certain fish.
Prince Charles, heir to the British throne, is one of the more visible public figures to voice concerns over the potentially "enormous environmental and social risks" of nanotechnology.
However, proponents counter that the risks associated with self-replicating machines have been much exaggerated.
"Artificial self-replication is already a risk when it comes to computer viruses and genetically modified crops," Lipson, the Cornell researcher, said. "I think that mechanical self-replication is far down the priority list. There are plenty of other things to worry about before this."
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