Domestication of the Dog, Part I, The

Phi Kappa Phi Forum, Summer 2004 by Tiffany-Castiglioni, Evelyn

Though breeders were selected for tameness alone, an astonishing result of the farm-fox study was the appearance of phenotypic, or physical and biochemical, changes in some elite animals. Some of these foxes were spotted or patched black and white (piebald, see Figure 1) or had a white star on their foreheads. In addition, many of the new, unusual physical traits in the elite foxes appear to be the retention of kit-like characteristics in the adult, such as barking, floppy ears, tails that curve over the back, broader heads relative to length, shorter snouts, and smaller skulls. This phenomenon is called pedomorphism and is believed to be a feature common to many domestic mammals. These characteristics, rare in the fearful fox population, increased in numbers in each generation as the experiment progressed. Reproductive behavior also changed, with elite foxes reaching puberty earlier and having longer breeding seasons.

The physiological basis for these changes is the subject of ongoing study by Russian investigators, who have shown that the foxes' endocrine (hormone-secreting) systems and brain chemistry have changed. Elite foxes have lower stress-hormone levels than fearful foxes, and their brains have higher levels of the neurotransmitter serotonin, which is associated with calmness. In selecting and breeding animals that were friendly to humans, the genetic pool has become skewed towards a different response of the adrenal cortex towards humans. The wonder is that this process took only thirty to thirty-five generations of foxes and forty years of human time.

To become the commensal species that does and humans are, that is to say, species that live together to their mutual benefit, an event unique in natural history took place. Our human forebears and dogs' wolf forebears must have been resourceful beings to establish this enduring relationship. The relationship is still evolving, and with recent revelations from canine genomics, it is evolving in unforeseen ways. In my next column I shall discuss two topics: speculations on how wolves became proto-dogs and the creation of pure breeds. Purebred dogs have been created by generations of tightly regulated breeding to a conformational standard. The offshoot of this activity seems to be new models for human hereditary diseases. I'll be back in six months with more.

Evelyn Tiffany-Castiglioni, PhD, is associate dean for Undergraduate Education and head of the Department of Veterinary Anatomy and Public Health, College of Veterinary Medicine, Texas A&M University. She conducts research on the neurotoxicity of environmental contaminants. She is on the editorial boards of Neurotoxicity and the International Journal of Developmental Neuroscience.

Authors Note: I thank Dr. Bhanu Chowdhary and Dr. Kimberly Greer at Texas A&M University for providing information about canine genomics and evolution.