Much of what we know about the physiological and behavioral effects of domestication comes from the farm fox studies conducted by a Russian team of geneticists, led by Dmitre Belyaev and Lyudmila Trut.

A mere 40 years and 30-35 generations of breeding wild foxes strictly for friendliness toward humans resulted in animals with behaviors closer to that of domestic dogs than their wild cohorts. More importantly, these studies offer four valuable insights for veterinary practitioners.

1. Domesticated animals are less mature

Domestication results in individuals who are physiologically and behaviorally immature (a state referred to as "neoteny") relative to their ancestors. Physiologically, a steady drop in the activity level of the adrenal cortex of the foxes occurred as they became friendlier.

After 12 generations of selective breeding, basal corticosteroid levels were more than half that of the control group. By the end of 30-35 generations, these values had halved again.

At the same time, the adrenal cortex did not respond as quickly when the domesticated animals were subjected to emotional stress. The domesticated foxes also had higher levels of serotonin.

In addition to various developmental windows remaining open longer as a function of domestication, the process delayed the opening of the foxes' eyes and ears. The pinnae of the domesticated animals also became longer and floppier.

Loss of pigment occurred, and the single-season breeding cycle triggered by phototropic cues gave way to a more irregular pattern; some foxes cycled twice a year like some domestic dogs. Sexual dimorphism, i.e. differences between male and female cranial morphology, also disappeared. Muzzles shortened, undershot jaws and overbites became more common, coat colors changed, and tails curved.

One way to interpret these changes is that domestication prepares an animal to function in a physiologically as well as behaviorally dependent state relative to humans. Because humans will meet the animals' basic needs — food, water, shelter, mates — this would relieve domesticated animal of the stress associated with obtaining these.

A willingness to interact with people also raises the possibility that animals once environmentally limited to reproducing and raising one viable litter per year could reproduce more often. Additionally, higher serotonin levels would support longer hours of sleep and lower sensitivity to changes in the more protected, less stressful human environment.

However, we also can appreciate how the effects of domestication may place contemporary companion animals at a disadvantage when it comes to dealing with stress. Many of my clients live complex lives that make ensuring a consistently beneficial response to their animals difficult to impossible.

Additionally, many of them want and believe they need their dogs' physical and emotional protection for some reason. Consequently, they want to keep that dependent human-canine relationship intact. It’s only the unintended consequences of that relationship — the aggression aimed at the wrong person, the destructive chewing (often involving valued articles that carry the owner’s scent), the counter-surfing and garbage-eating — that they want gone immediately if not sooner.

In these people’s minds, this not only seems right, but natural. Lacking knowledge of normal companion animal behavior, they believe this is what these animals evolved to do.

This raises the question: Could the increased incidence of adrenal, thyroid and pancreatic disease in domestic animals, in part, be a function of this inverse relationship between the domestic animal’s decreased ability to handle such stress and the increased amount of it in the animal’s human environment?

Neoteny doesn’t necessarily mean that domestic animals necessary look or act like wild baby animals of comparable species — although some breeders seem to be consciously or subconsciously moving in that direction.

Behaviors in domestic dogs and cats, for example, represent a conglomerate of immature, mature and everything between when compared to their wild ancestors and cohorts. Sometimes adult and infantile behaviors may be combined to communicate a completely different message than either behavior does separately.

While this may signal an animal in conflict, it also may result because the animal’s grasp of any normal behavior associated with a particular situation is sufficiently weak that the animal takes a "whatever works" approach. If this achieves the desired response, the animal repeats it. If not, the animal tries something else.

2. The mind and body are connected

The domestication studies make it clear that animals evolve as mind-body units. When the animal’s behavior changed, so did the animal’s looks and physiology. And the converse is also true: a change in physiology will change behavior.

(Note: Animal studies of the biochemistry of the receptors associated with emotions demonstrate a similar relationship. Changes in emotions change physiology as much as changes in physiology change emotions.)

Of all companion animal breeders, those who breed Persian cats seem to possess the best grasp of this reality. These animals are shown in color-specific classes because of the noticeable differences in conformation and temperament that arose when the animals were bred strictly for eye and coat color.

On the other hand, purebred dog breeders sometimes seem to possess the least awareness of this relationship. Most practitioners are well aware of color-related medical problems within certain canine breeds. Some practitioners and breeders also may recognize color-related temperaments and their associated behavioral differences, but this phenomenon has gained much less attention thus far.

Aside from breed-related relevance, the inextricable relationship between animal behavior, physiology and the human-animal bond also explains why the first sign of illness or injury perceived by clients is often a change in the animal’s behavior. Similarly, clients attuned to their animals and experienced clinicians are more hesitant to accept diagnostic test results that indicate an animal is healthy if the animal displays behavior that suggests that the animal is not.

Thus, the more scientifically correct response to the ADR — "Ain’t doin' right" — patient with normal bloodwork or other diagnostic test results isn’t that the animal is fine. The correct response is to acknowledge the validity of the client’s contention that something is bothering the animal rather than dismissing it.

This then gives rise to two questions:

• Does this occur because the current (or available) technology lacks the sensitivity to determine a medical cause?
• Or does the animal’s change in behavior reflect a change in the animal’s physical or mental/emotional environment?

The latter changes might include an increase in the wildlife or free-roaming domestic animal population, additions or losses in the human population, or remodeling that destroys scent and other perceptual cues an older or physically impaired animal depends on for stability in that environment.

3. Domestication is a dynamic process

Domestication doesn’t represent a definitive change that happened to certain animals X years ago. Pictures of purebred dogs and cats today and 50 years ago demonstrate that it represents ongoing process, and perhaps even one that is accelerating in response to multiple factors.

In my area, the longer muzzle, shorter ears and smaller eyes common in hunting Labrador and golden retrievers prior to their entrance into the pet realm has given away to conformation sometimes affectionately referred to as "block-headed." Not only do these animals look different and often more immature, but the fox studies remind us that corresponding physiological changes most likely accompany that look.

For example, the more infantile features could embody a more immature immune response or one that matures more slowly. This could have consequences for the animal’s ability to handle stress and susceptibility to conditions with an immune component such allergies and auto-immune or immune-deficiency diseases. Perhaps even some forms of cancer.

It also might raise questions regarding the soundness of separating kittens and puppies from their mothers at eight weeks of age, let alone younger.

4. The human-animal relationship

Another sometimes-overlooked aspect of the domestication studies concerns the ideal relationship between humans and domesticated animals, and especially those with whom we share our homes and even our beds. Because we have selectively bred these animals for neoteny for thousands of years, logic says the most natural way to relate to them would be as mature parents of the animal’s own species.

However, this often has not been the case. More often people embraced reward/punishment teaching systems that support a competitive rather than a biologically-based parental relationship. Either that or people adopt a highly anthropocentric rather than animal-specific parental approach and relate to their animals as if they were some sort of fur-covered mentally challenged little humanoid.

Both approaches may destabilize some animals’ health and behavior.

Finally, we can’t overlook any effect our own ongoing domestication may have on how we breed and relate to companion animals. Increasingly, people perceive companion animals as a source of their own physiological, behavioral and emotional security.

But logic also reminds us that some animals primed by domestication to live in physically, behaviorally and emotionally secure human environments may find fulfilling those human expectations difficult. And when this occurs, the animal’s veterinarian no doubt will be among the first to hear about it.

Nothing will make unraveling these often complex cases easy. However, understanding the role domestication plays can make them less frustrating for practitioners.