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Humans do it, bacteria do it, even viruses do it: they make copies of themselves. Now US researchers have built a flexible robot that can perform the same trick.

It's not the first self-replicating robot ever built, says Hod Lipson of Cornell University, who led the study. But previous machines with the capacity for copying themselves have been very simple, often spreading out in only two dimensions. And more complex devices existed only in computer simulations, not reality.

Lipson's robot, which is made of four cubes stacked on top of each other, has a flexible, three-dimensional design. "There is a whole world of possible machines," says Lipson, pointing out that you could make much more complex robots in the same way simply by using more cubes.

The researchers envisage machines that automatically repair themselves, making them ideal for use in hazardous environments such as outer space. The current version of Lipson's robot isn't quite up to that futuristic goal. But it is a good step forward, says Moshe Sipper, a self-replication expert at Ben-Gurion University in Beer Sheva, Israel.

Cubic copy

Lipson's robot consists of four cubes, each 10-cm to a side, which are sliced diagonally into halves that can rotate against each other. This allows the robot to change shape, he reports in Nature1. Provided it is fed with cubes, the robot can create a copy of itself within a few minutes.

To build a replica, a 'parent' robot bends down and places its own uppermost cube on the table next to it. This becomes the base of the 'child' robot. The parent then picks up a new cube, using electromagnets powered from contacts on the surface of the table, and stacks it on top of the child base. During this process, the child bends down to help the parent add cubes whenever it becomes too tall for the parent to reach. In the end, two four-cube columns stand next to each other.

Lipson says the cubes contain the electronic equivalent of DNA: a microprocessor with a memory of the robot's body plan and instructions on what to do during self-replication. By adjusting this information, it should be possible to make reproducing machines in any number of shapes or sizes, says Lipson. A robot made up of hundreds of much smaller blocks would have a huge number of shape options available to it.

Transformers

Lipson's machines have some limitations. They are particularly dependent on being fed new blocks, for example. Unlike living creatures, they can't forage for food or building material. And because the process is preprogrammed, if extra blocks aren't in precisely the right place at the right time, then assembly will stop.

Next, Lipson hopes to test whether unprogrammed versions of the cubes could evolve the ability to self-replicate, by having random changes introduced to their electronic DNA. "It would be interesting to see if they spontaneously learn how to self-reproduce using evolutionary principles," he says.

Such studies may trouble those who fear that tiny self-replicating robots will one day run riot, as they do in thrillers such as Michael Crichton's Prey. "As a matter of public policy, artificial machine systems should not be built that evolve, so that there can be no danger of them escaping our control," says Robert Freitas, co-author of a book on self-replicating machines, who works at the Institute for Molecular Manufacturing in Palo Alto, California.

But Lipson adds that there really is no need to worry. "I don't think we're anywhere near that," he says.

http://www.nature.com/news/2005/050509/multimedia/050509-6-m1.html[URL][/URL]