ONE of the most popular characters in “Dr Who”, a British television science-fiction series, was a robot dog called K9. On June 1st, science fiction became science fact when Sony launched its latest product, Aibo. Described as “a one-of-a-kind artificially intelligent pal”, Aibo is a dog that never needs to be walked, fed or washed. Nor does it make a mess or get into fights with other dogs. It has stereo microphones for ears, can recognise colours and shapes, and emits a variety of bleeps and chirps. A sensor in its head can distinguish between an amiable pat and a reproachful slap. And the pause button on its chest means it can be switched off and left in a cupboard when you go on holiday.

A good joke, and a profitable one (the first batch of 3,000 machines, priced at just over $2,000 each, sold out within 20 minutes). But behind the marketing spiel about Aibo's autonomous behaviour patterns, simulated emotions and instincts, “lovable shape” and “four highly expressive legs”, lurks a serious point. Aibo is merely the latest example of a robot inspired by biology.

This makes sense. Millions of years of evolution have already solved difficult design problems in locomotion, manipulation, sensing and navigation in almost every environment in which a robot might conceivably need to operate. Accordingly, a menagerie of “biomorphic” robots can now be found scuttling, squirming and swimming in laboratories all round the world.

For instance, several separate efforts are now under way to build robotic fish that could be used to locate mines or take environmental readings. Understanding how fish manage to swim so quickly but expend so little energy could also lead to new propulsion systems for ships and submarines. This may explain why Mitsubishi Heavy Industries, a Japanese company whose activities include shipbuilding, has spent four years and $1m building an incredibly lifelike robotic sea bream. (The company now plans to move on to re-creating extinct fish for display in museums.) Similarly inspired robotic pike and tuna have been built at the Massachusetts Institute of Technology.

But a robot does not have to look like an animal to borrow useful ideas from the animal kingdom. Mark Tilden and his colleagues at Los Alamos National Laboratory in New Mexico, who have been building animal-like robots for years, have now applied their knowledge to create a system that will operate in one of the environments that natural selection has not yet managed to penetrate—outer space. Their latest robot is designed to keep satellites on station.

Dr Tilden is concerned not so much with what animals look like as with how their nervous systems work. As every schoolboy discovers, pulling some of the legs off a spider does not stop it walking. Its nervous circuitry can adjust to such injuries. That is because, unlike most modern computers (including those that control Aibo), much of that circuitry is analogue rather than digital.

In a digital computer, information is sent around as discrete bits and bytes. If a critical bit goes missing, and the program has not been prepared in advance for the possibility of such a loss, it breaks down. With analogue circuitry, however, there is no such thing as an independent, critical piece of data—everything is coupled together as one continuous flow of current. If some information goes missing (for example, because a schoolboy has amputated a leg), the output will change—but it could still be meaningful. Dr Tilden's robots use cheap and basic electronic components such as transistors, resistors and capacitors, rather than fancy microelectronic silicon chips. Yet their behaviour is so life-like that they can sometimes “spook” those afraid of real spiders.

These robots, like Aibo, are toys. But a satellite-navigation system is a serious, practical application. Dr Tilden's design for such a system is being tested in an experimental Swedish satellite called Hugin. Its task is to keep Hugin's electricity-generating solar panels pointed at the sun. It has a dozen light-sensors, each connected to a circuit whose natural oscillation is modulated by the strength of the incoming illumination. Those circuits, in turn, control the satellite's attitude jets. If the satellite moves off station, the amount of light falling on the sensors will change, and its analogue circuitry will tell the jets how much to fire to bring it round to face the correct way. It may not be as photogenic as a robot dog, but it is certainly a lot more useful.