Why Chihuahuas?

The origin of the domestic dog, also known as Canis familiaris, has been a source of much controversy over the years. Based on historical archeological findings, the first record of canine domestication dates back to 12000-14000 years ago. Current research suggests that different breeds of domesticated canines come from varied distinct lineages, or clades, connected to the Canis lupus Long before these results had been obtained, workers had assumed that New World domestic dogs had evolved from North American gray wolves while Old World breeds had developed independently from Eurasian counterparts. Surprisingly, this theory may need to be revised. Not only did others discover evidence that Canis familiaris is composed of multiple lineages, but also that the majority of New World 'native' breeds actually map onto several 'Old World' clades. Very few breeds turn out to be derived from North American gray wolves. It would appear that more than one Eurasian variety of domestic dog crossed into North America along with humans thousands of years ago. This may not, however, have been the only introduction of European genes, as colonists were reluctant to uphold the pure breeds native to the New World when they began settlement in the 15th century. One of the few native breeds that did not mix with European stock is the small Mexican hairless, or xoloitzcunitle, a close relative of the Chihuahua. The Chihuahua itself has been crossed with other breeds, most notably brachycephalic forms like the Pekingnese and Pug, giving it a shorter muzzle and relatively flattened face. Other well-known characteristics of the Chihuahua come as the result of the breed’s dwarfism. Most conspicuous is the fontanelle located where the large sagittal crest is found in other canids. In most mammals, as individuals make the transition from juvenile to adult, the bones forming the skull ossify and fuse together. In a Chihuahua’s skull this ossification is usually incomplete, leaving the breed with a gap instead of a suture and a round, broad puppy-like head. A basic dog skull looks quite different, resembling more of an elongate box, but all breeds vary somewhat from this general plan.

Neoteny and Accelerated Degeneration

The human desire to accentuate traits like dwarfism appears to have been introduced into breeding spaces throughout most of the latter half of the history of canine breeding programs. As one of the first animal to be domesticated, dogs have consistently been selected for these trait-selective programs. Neoteny, a phenomenon demonstrated across the entire biological spectrum, occurs when an organism continues to display juvenile traits even as it sexually matures. Toy dogs, especially the modern-day Chihuahua, are an extreme case of this phenomenon. It has been posited that humans possess an innate “cute response” that engenders nurturing feelings toward helpless-looking creatures—a quality advantageous in a species with exceedingly altricial, or undeveloped, offspring. Upon examination, toy dogs seem tailored to super stimulate just that instinct. They are, in essence, fetuses ex utero. Their foreshortened limbs and faces, limp ears, and, in some cases, underdeveloped cardiovascular and respiratory systems are all typical of fetal animals.A basic dog skull looks quite different, resembling more of an elongate box.The inevitable result of these breeding programs, which may indeed surpass their parents in miniaturization, are beset by a grim array of accompanying congenital disorders decidedly unsuited to accessorizing. Only few animals have been shown to live their entire adulthood in an advanced sate of permanent neoteny, namely the Axolotl and Olm, which retain their juvenile aquatic form throughout their entire lifespan. However, these ae only minor outliers from what is observed in the mammalian species. It goes without saying that the most prevalent form of this phenomenon can be seen in domesticated mammalian species, particularly in dogs.