Idiopathic behaviors: pica, acral lick dermatitis, cribbing, separation anxiety and aggression (Proceedings)
The term idiopathic is usually attached to behaviors such as acral lick dermatitis, pica, psychogenic alopecia and cribbing to denote an undetermined origin. While these behaviors are technically unexplained, they have correlations that hint at causality. The three factors that each of these behaviors share are selective breeding, the absence of culling through natural selection and close confinement.
Abnormal Ingestive Behavior: Vestigial Shadows?
Several behaviors prominent in wild canid populations remain in domestic dogs as nonfunctional, apparently vestigial behaviors. Often, the "abnormal" behavior coexists concurrently with perfectly normal behavior, such as a dog that eats socks but also eats dog food. Pica is prominent in the list of behaviors that may once have had a function but now exists as a distorted version of its original form. Likewise, copraphagia has a logical benefit to predators that also scavenge and eat carrion to cover times when prey is scarce. Gorging is considered abnormal ingestive behavior in dogs and is routine for wolves whose prey-dependent life-style alternates between starving and gorging. Anorexia is a logical opposite of gorging, but also may be explainable as a vestigial remnant of a normal condition. Wolves are migratory hunters who annually experience feast contrasted with famine. To go without food for several weeks without losing muscle tone or organ function can be the difference between survival and death. The ability to ignore the sensations associated with hunger may be adaptive in the wild and maladaptive in captivity. The physiological functions that trigger anorexia may be the balancing mechanism that limits pica, causing a hungry coyote to not eat poison-laced lamb. In captivity, this balance is meaningless as animals are provided with daily feedings that do not mirror the sporadic acquisition of food commonly found in nature.From a biological perspective, these abnormal ingestive behaviors may possibly be disjointed forms of naturally occurring behavior. The process of domestication virtually insures the destruction of a balanced behavioral repertoire. Many domesticated animals are maintained by their owners, specifically because they possess artificially reinforced maladaptive behaviors. Field pointers are prevented from flushing birds – the logical result of their artificially strengthened stalking behavior. Likewise, Australian Cattle Dogs have been selected for such a precisely modified predatory chase that if returned to the wild, would continue to bite the planted foot of a prey animal rather than hamstringing it. Both of these breeds possess intentionally unbalanced behavioral repertoires that only vaguely resemble their ancestors. While creating these special behaviors in the absence of natural selection, other physical and behavioral traits may come along for the ride because in captivity they are no longer counter-survival.
Pica may also be an example of a natural behavior, imbalanced by captivity. In his extensive research, Ivan Pavlov tested the notion that dogs instinctively know what to eat. Pavlov kept a puppy on a milk diet until it was six months of age – well beyond normal weaning. He then offered a plate of meat-paste to the dog. The dog sniffed the paste but did not try to eat it. Pavlov then put a small amount of the paste in the dog's mouth. The dog greedily ate the rest of the paste. The implication is that puppy mouthing is the means by which dogs learn what is edible and what is not. The result is a dog that is instinctively willing to put its mouth on novel objects. Whether the dog will ingest the item is not related to its nutritional value. Some dogs ingest plainly indigestible items such as nylabones, Kong toys, sheet metal and plastic. If copraphagy is a sub-set of general pica, it explains why a direct connection between ingestion and nutrition is not necessary to explain the behavior. It may simply be that the behavior of "put things in your mouth and chew them up" exists in all dogs. They offer this behavior, untaught and unreinforced, like all other instinctive behaviors. As with cat chasing, hole digging and door-protecting, all that is needed to cause the behavior is an eliciting stimulus. The failure to produce direct consequences of eating a sock is fundamentally no different than the consequences of a Greyhound chasing fake bunnies yet never receiving nutritional benefit from the behavior.