Why Don't Giraffes Fall Over More Often?

One of the major reasons psychologists think we have mental representations is to overcome delays in the nervous system. Information has to come from sensors such as the retina and travel the distance to the visual cortex. This takes time. That information must then be processed and combined with other information to generate adaptive responses. This takes time. Delays in a control system that relies on feedback are a big problem for stability. The more time it takes for feedback about how well you are doing to reach the brain, the less relevant that feedback information is - it's no longer about what you're doing right now. This makes it difficult to make sensible error corrections and it ups the chances that something will go badly wrong. A lot of people therefore claim that the only solution is prediction, and there's a strong research industry investigating how the nervous system predicts so well.
There are, however, embodied solutions to delays in nervous systems. Prospective control is the strategy of controlling your behavior using information about how events are unfolding over time. If you have information about this dynamic, then perceiving something at time t tells you something useful about what's happening at time t+delay and with a little calibration you're running in real time. There is a lot of evidence that this is a very common strategy; the evidence mostly comes from interception tasks, because identifying the dynamics and the information that dynamic might be producing is a tractable problem for psychologists. Prospective control isn't always an option though; sometimes there isn't information about what's going to happen next (for example, there's no information about upcoming changes in friction, which is what makes ice so dangerous). In addition, prospective control still requires information to get into and be processed by the nervous system, so delays might still be an issue. 
Motifs are a neural architectural solution to delays; the brain takes a little bit of time to set this organisation up but then runs with zero lag between widely spread networks modules.I don't yet know enough about these to know how widespread or effective a solution they are, however.

Giraffes- why don't they fall over more often?

One interesting model system for thinking about the consequences of neural delays is the giraffe. Adults giraffes stand 5-6m tall, so the feet are a long way from the brain. Anything that happens to the feet as they walk (say, tripping on a tree root) will potentially not be registered fast enough for the brain to issue a response.

Do giraffes, in fact, fall over much? I've been poking around Google Scholar and Twitter with no luck; there just doesn't seem to be much research on giraffe locomotion. Alexander chased some in a car to get them up to top speed and do some biomechanical analysis (because he is awesome and unafraid of the obvious experiment; Alexander, Langman & Jayes, 2009) but I don't think any fell over. There's some work on the basic mechanics of giraffe locomotion, but there just isn't much information about how well the whole thing works.

Their long legs are a fact, though, so why don't giraffes fall over often enough that people (not to mention evolution) notice it as a thing?

Faster neurons?
One option is to invest in more and faster neurons. However, More et al (2013) measured the conduction velocities of 8 male giraffes and found that they have the expected number and the speeds averaged around 50m/s, fairly typical for mammals. Giraffes have not invested in this solution, suggesting that it either wasn't an option or they have another solution that works better. More et al don't have an alternative beyond falling back on prediction, though (this story featured on Quirks & Quarks a while ago, and it's what got me thinking about this topic).

Cautious gait?

Their gait is a very typical quadruped lateral sequence gait (hindlimb comes up and followed right away by the forelimb on the same side (video; thanks for the help here, John Hutchinson). Do they have behavioural modifications to this? Do they perhaps only ever walk slowly, to give themselves time to cope with any problems? Typical walking seems to be quite chilled out (video) so that fits. But chilled out walking is pretty common in animals that don't have to be anywhere immediately (it conserves energy) and giraffes can run at 60km/h and sustain 50km/h for some distance (video; Wikipedia has some references). 
That video shows them turning and maneuvering quite well but in the open and not at full speed as they run through the trees. They do live in fairly well behaved terrain; flat grasslands. There isn't a lot to trip them, and they don't move at full speed when there is. But other than these fairly normal behaviours, giraffes don't seem to be doing anything in particular to cope with these neural delays. This suggests that the delays aren't actually a problem.

Maybe the brain isn't where it's at  

Neural delays are potentially a problem for a wide variety of animals. One known solution is to offload responsibility for limb control onto the local limb dynamics. For example, arms are often arranged as low dimensional damped mass springs; this allows them to oscillate stably with minimal control requirements, and they respond to perturbations without explicit instructions. They simply do what nonlinear dynamical systems do and self-reorganise themselves back to where they were, if they can. This sort of solution is common and it works well (another example is the equilibium point control hypothesis, e.g. Feldman, 1986). Giraffes almost certainly do this kind of thing too. 
Another solution is to shorten the distance to the neural control circuitry. The main solution here is the spinal cord, which recent research has revealed to be a complex and very sophisticated piece of neural hardware and not just a waystation for signals heading to cortex.
Another related idea (from Sabrina) for which I have no evidence: If a giraffe trips, where does the most relevant information come from? Are they built in a way that the information about a trip or perturbation is actually generated at, say, the hip? 
A call for some good biology followups
Cognitive science loves a good case study that demonstrates a point, and whatever the giraffe is doing to cope with the fact that it's brain is 5m away from it's feet will be a great demonstration of how to cope with neural delays. Prediction is always an option, but the data typically never favour it and it's an unstable solution for the same reason as delays are a problem: it's hard to make sure the prediction is about what actually happens. An embodied approach using our four research steps (Wilson & Golonka, 2013, pg. 2-3) can guide research here as readily as it can in psychology, and we would love to see biologists exploring this question comprehensively and without jumping straight to prediction as the only alternative.

References

Alexander, R. McN., Langman, V. A., & Jayes, A. S. (2009). Fast locomotion of some African ungulates. Journal of Zoology, 183(3), 291-300. Link (££)
Feldman, A. (1986).  Once more on the equilibrium-point hypothesis (lambda model) for motor control. Journal of Motor Behavior, 18(1), 17-54. Link (££)

More H.L., O'Connor S.M., Brondum E., Wang T., Bertelsen M.F., Grondahl C., Kastberg K., Horlyck A., Funder J. & Donelan J.M. & (2013). Sensorimotor responsiveness and resolution in the giraffe, Journal of Experimental Biology, 216 (6) 1003-1011. DOI: 10.1242/jeb.067231

Wilson A.D. & Golonka S. (2013). Embodied Cognition is Not What you Think It Is, Frontiers in Psychology, 4 DOI: 10.3389/fpsyg.2013.00058