Learning new skills the natural way (Image: NaturalMotion)





Video: Walking monsters

Monsters and aliens that move more realistically than ever before are coming soon to a screen near you.

Thanks to “artificial evolution”, computer-generated humans in a number of recent Hollywood epics and video games have been able to interact with each other and their environments in a more life-like way.


Now NaturalMotion, whose animation technique was used in the films Troy and Poseidon, has shown its method can equally be applied to non-human body shapes – for instance, bipedal monsters (see video, above).

“A monster might have a completely different overall body mass distribution,” or different limb proportions to a human, says Torsten Reil, the firm’s CEO. “It’s equivalent to me waking up in a child’s body and being able to balance and look natural straightaway.”

State-of-the-art animation for non-human film characters usually involves filming real actors wearing fluorescent motion capture sensors from several angles. Still art work of, say a monster, is mapped onto the footage and made to move using the movement of these sensors at key points such as elbows and knees as a guide.

Computer games use this technique but realism is limited because a number of set sequences must be applied in a virtually limitless range of situations.

NaturalMotion, whose origins are in the zoology department at the University of Oxford, UK, took a radically different approach.

Virtual skeletons

Reil and colleagues began with 100 identical virtual skeletons, complete with muscles controlled by a simulated network of a few hundred motor nerves.

They then attributed random values to the strength of connections between key nerves involved in movement in each skeleton and made each perform a task – for instance, walking.

The five that managed to walk furthest without falling were labelled the “most fit” and used to spawn the next generation.

These were each copied 20 times to create another population of 100, and in each individual, a subset of the connections between nerves were altered to mimic the natural variation that might be found in the next generation of a biological species.

The new population then repeats the walking task, with the best performers going on to create the next generation.

Over several generations, a skeleton with all the grace of a shambolic drunkard will ultimately give rise to a nimble walker.

On the fly

“We’ve used concepts from biology and physics to unshackle games,” says Reil. By “evolving” algorithms that can animate characters entirely on the fly rather than relying on a handful of pre-recorded sequences, he says game worlds will become more realistic.

Since 2001, the animated humans NaturalMotion produces have evolved to perform a range of tasks such as balancing, walking, and interacting with their environment – for instance, by anticipating a collision and bracing themselves in readiness. Those skills are put to use in the firm’s American football Backbreaker computer game, due for release in June.

The company’s latest discovery is an evolutionary shortcut of sorts – a behaviour “evolved” to fit a given skeleton can be applied to radically different body shapes.

“We can add additional joints – we might give a leg two knees,” adds Reil. “And recently I’ve been looking at how a three-legged stool walks and balances. It looks odd, and makes you realise why biology doesn’t go for three legs.”

NaturalMotion’s approach could help to animate alien bodies in computer games, but Reil says it’s also possible the approach could have an impact for biological research – for instance, by animating in a range of extinct animals.