All dog breeds are the result of the convergence of evolutionary factors and miscegenation. Some breeds are man-made and others are naturally made, with little influence on their form and function from the ability of natural selection. For example, the Bulldog breed was a “backward” breed and was bred to create a livelier, longer-legged version of the original dog breed.
Of the Tibetan breeds, the Lhasa Apso, the Tibetan terrier, is more a product of evolution than human influence. Of the five recognized Tibetan breeds; the Tibetan Terrier, the Tibetan Spaniel, the Do-Khyi (Tibetan Mastiff), the Lhasa Apso and the Shih Tzu, the Lhasa is the breed most directly influenced by the harsh climatic conditions of the Tibetan Himalayas.
There are many reasons why this happened. Lhasas were first selectively bred by Tibetans about 800 years ago in the city of Lhasa, the capital and home of the Dalai Lamas. However, the breed has its origins around 2,000 years ago in the Tibetan environment.
Second, historians speculate a lot about whether these Tibetans actually attempted the sophisticated practice of selective breeding that is so popular today. The early Tibetans were hunters and herders who relied on Tibetan dogs to hunt, protect herds, and serve as watchdogs and companions to humans. The natural tendencies of the Tibetan races, shaped by evolutionary forces, were more than enough to ensure the survival tasks facing the Tibetans.
Third, the physical form of a Lhasa Apso has remained largely unchanged from its original form, because it can still conserve heat when needed. Cold-adapted animals have bodies with a higher ratio of muscle to fat, compared to the bone mass of other breeds that have had to adapt to a warmer environment.
The amount of heat produced by an animal is directly proportional to its weight or volume. The larger the body, the more heat it produces. What is known is that heat loss is also proportional to the surface area of the body, the more surface area there is, the faster heat is lost. Conserving heat is a function of the ratio of body mass to area, with the one with the most surface area losing heat the fastest.
Because a Lhasa Apso’s body is shorter and rounder, it has less surface area than its warmer environment cousins of equal weight and longer legs. Those same forces also govern body type; people of Eskimo lineage have shorter, stockier bodies and less surface mass than an equatorial person of equal weight who has a longer, slimmer body and higher surface area. In short, to limit heat loss in the cold, it is best for an animal to have as compact a body and short legs as possible.
Nature has adapted the body of a Lhasa Apso to suit the hills and villages of the Himalayan Highlands. This breed is built for endurance, not speed, for walking, jumping, and climbing, and not like the bodies of other dog breeds.