Viking Health Care: Veterinary edition

It was noted many years ago by an astute naturalist that when a horse is bisected by the rapid descent of a portcullis, the sudden absence of its hindquarters may not immediately register with the beast's dim little brain (for horses are not the brightest of foodstuffs our animule friends), with the compensatory changes of balance and fine limb-movement timing required to remain upright and in motion being handled at the level of the shoulders.

Naturally bipedal horse, or double amputee? Only the "My Little Pony" apotemnophila fetishists know for sure

There is a broader lesson here about the extent of self-organisation and local autonomy involved in mammal locomotion, from swimming to galloping. The precise sequences of muscle contractions to produce a stable, periodic gait arise spontaneously among neural networks in the spinal cord rather than being sent down from the brain. At this point it behooves you** to read about central pattern generators. Come back when you've done that.

It transpires that many Icelandic horses are homozygous for a mutation on the DMRT3 gene, which controls the development of spinal neurons. The results are TOTALLY PREDICTABLE -- they have fewer of the commissural interneurons involved in cross-lateral coordination; their left hooves are less aware of what their right hooves are doing. This makes it possible for them to override the usual left / right timing constraints and perform the skeið or flugskeið (also known as 'pacing' among horses that don't speak Icelandic), not to mention the tölt, a kind of amble.

The mutation is not necessarily an advantageous one; it carries the downside that Icelandic ponies are not as adept at the more conventional equine gaits (Supplementary Table 5). This explains why Iceland has never won an Olympic Gold medal in dressage.

Grettir's Saga relates how Grettir attempted to produce these extra gaits by rewiring the spinal circuitry of Kengala the weatherwise mare,*** using the primitive equipment available to Viking neuroscientists.

Sadly, this pioneering line of research was not pursued further due to the hostile response from Ásmundr (father of Grettir, owner of Kengala and probably a climate-change alarmist). A millennium later and Icelanders are still speaking of how Ásmundr slammed the stable gait after the horse had bolted.

Bonus Keats-&-Chapman punchline: * Below: Unintelligence of horses proven by their failure to learn to count up to 4, even when the numbers are fastened to cages strapped over the subjects' heads. ** I didn't hear a laugh from that man over there.

*** Kengala was "so wise about the weather and the rain that a storm invariably follows when she refuses to go out to graze".