I was on a trekking holiday in the Himalayas. Because there are no roads, goods have to be carried either on porters鈥� backs or by pony trains. The tracks are steep, often consisting of uneven steps. The ponies need to keep looking at the track immediately ahead in order to position their front hooves. But how do they know where to place their hind hooves?
鈥� This is a vital skill for large quadrupeds for whom tripping is dangerous, such as horses and elephants, but also for animals that must stalk quietly when hunting, such as wildcats. These animals automatically guide the hind leg over obstacles the forefoot has already negotiated. Surreptitiously remove an obstacle once a cat鈥檚 forefoot has passed over, and the hind leg unnecessarily follows a trajectory over the absent obstacle; but introduce an obstacle after the foreleg has passed and the hind leg bumps into it.
The characteristic walking gait of tetrapods plants the hind foot just behind the forefoot. Usually footing will be secure there, because it has already been tested. Similarly, chameleons negotiate a wide gap by anchoring their tails and hind legs, reaching out with their forelegs, then swinging the hind legs forward to where the forelegs have gripped. Only then does the tail let go.
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Galloping is an emergency gait and accordingly riskier, often with rear feet landing well ahead of forefeet, but even then most large animals are surprisingly good at directing their feet. Small prey animals such as some rodents have a contrasting strategy. They systematically practise panic retreats along established paths so that they know the location of every pebble. This means that in emergencies when noise is no consideration they can flee blindly at top speed.
Jon Richfield, Somerset West, South Africa
鈥� A horse has a number of gaits, as humans have when walking and running. In the walk and the trot, the rear foot falls at almost exactly the same place the front foot on the same side was positioned. Thus a horse trained on difficult terrain will select a foothold for the front foot, and be able to aim its back foot at that spot without looking.
It relies on , the ability by which humans and other animals can unconsciously sense the position of joints, and via the tension of our muscles put a finger on our nose, or swap an object between our hands, without looking.
However, for horses this does not work at faster gaits such as cantering and galloping, and a horse won鈥檛 go this fast on difficult terrain, nor would its rider want it to!
You can see different gaits at .
John Davies, Lancaster, UK
鈥� Many years ago, I ran down a rocky mountain path and was very aware of the need to place my feet strategically to avoid injuring myself. I noticed that I wasn鈥檛 looking at feet my at all 鈥� I was looking a pace or two ahead. It seemed that, having planned a step, my brain planned future steps before the first one had even been executed.
鈥淚t seemed that my brain planned future steps before the first one had even been executed鈥�
I wondered whether similar planning happened in easier walking situations. Back in town, I discovered that, as I walked along, I could pick a crack in the pavement about five steps ahead and instinctively predict with a high level of success which foot would step on the crack, or, if my legs were going to straddle the crack, which would be the leading foot. And this was happening having never tried the task before.
This all suggests that walking involves much more forward planning than we are conscious of.
Ben Craven, Menstrie, Clackmannanshire, UK