Watch the horse's legs.
Which ones move together?
Now in slow motion. It's diagonally opposite pairs.
That's the trot. This one is exaggerated, but it's the trot pattern.
And it's not the only animal that uses that pattern.
The orangutan is in effect trotting upside down.
So we've understood two-legged animals
and now we've understood four-legged animals but now we want the lot.
We want to go to any number of legs.
We certainly want to be able to get up to six legs.
So here we have a six-legged creature.
Come on you. Here we go.
There we go.
Watch you move.
Watch the pattern of his legs. It's a stick insect.
And it's moving its legs in one of the standard patterns
that six-legged creatures move them.
OK, thanks, Ilya.
So, come this way.
Now what we have here is a robot. This is Darren Wen from the University of Reading.
This robot is Elmer and Elmer, when he warms up, is doing the tripod.
It takes him a little while because he has seen an obstacle, he saw the AT-AT.
Come on Elmer, do your thing.
Now he's doing a tripod, he's moving three legs at a time.
OK, Elmer, that's super. Let's turn you off.
Darren, thanks a lot for bringing Elmer along.
[Applause]
So let's just sum up what we saw there.
The insect with its six legs, there are certain patterns,
Elmer was doing the tripod. The tripod is like this.
Three legs, the other three legs, but they fit on the animal like that.
It just moves three at a time, three at a time, three at a time.
Nice stable gait.
So what's the big picture here?
What we want is to find out exactly why those patterns are coming up.
Now the way I've told that, I've made it sound as if
it's all to do with these pendulums, with the limbs, the legs.
But it isn't really the pendulums at all. It's not the legs.
It's got to be the neural circuitry, the nerve impulses that control those legs.
Because when you have legs, it's the signals
that get sent to the legs that actually make them move.
So, we've got an electronic millipede.
Had to switch him on.
The electronic millipede.
This is meant to be a kind of schematic representation of the animal's nervous system.
These lights are its nerve cells firing.
You should think of them as linked together in two long lines.
And linked across.
And we can do the mathematics of those things and see what the natural patterns are.
And imagine also that the legs move when ever the light lights up.
This would be a pronking millipede.
Not very realistic.
Now here's a more realistic millipede.
Travelling waves of nerve impulses going along the animal's body.
And the legs would move in the same pattern.
Let's just speed that up.
Now we've got faster waves going along.
Let me show you something interesting about that.
Suppose we just look at four of those nerve cells.
What are we seeing there? We're seeing the trot, diagonally opposite pairs.
And if we did that with a six-legged animal,
we're seeing the tripod.
So see what I mean about there being universal mathematical patterns.
The same pattern of waves, depending on the number of legs looks different to us.
It looks like a trot, looks like a tripod, it looks like a whole pile of millipede legs
moving.
And in fact, evolution might have done that for insects.
We know that the six legged insects started out
as creatures with lots and lots of segments.
And they lost segments over a period of time.
And if the pattern stayed with them as they lost the segments,
then you get the tripod.
It's not so clear that that's true for things like the horse.
Because the horse did not evolve from segmented creatures.
The horse probably evolved like all mammals from some kind of fish.
But the real message here that we've learnt is - it's all waves.
It's all patterns of travelling waves. That's the real pattern.
Now that's what Meggie, the Sussex robot does, too.
Meggie uses the same sort of travelling waves,
moves hre legs, just like our electronic millipede.
So Meggie has been borrowing a trick from nature.
And now we've got the famous Royal Institution wave machine.
Which Pippy and Ilya will bring on.
This is at least 50 years old.
It's featured many times in these lectures.
That's great, thanks.
This is the ultimate in coupled oscillators.
I waggle it at this end and the wave travels all the way along.
Here's our millipede.
Just do that again.
If I get too violent, it doesn't like it.
Travelling waves.
So that's the hidden secret, the mathematical secret of animal movement.
Travelling waves of nerve impulses going through some kind of circuitry,
just like the travelling waves of electronic impulses going through the millipede circuitry.
Let's just take a look at the millipede again.
We look at the millipede, what we see is those travelling waves of movement.
The legs are moving because that's what the nervous system is doing.
And once we've realised that, you don't even need legs.
Here's a sidewinder, moving across the desert, it's waves of muscular contraction.
It leaves trails in the sand to show how it moves.