All dog breeds are the results of converging evolutionary factors and interbreeding. Some breeds are man-manufactured and some are naturally made, there is hardly any influence on their form and function from the ability of natural selection. For example, the Bulldog breed was a "backward" breed and bred to create a long-legged, more livelier version of the original dog breed.
Of the Tibetan breeds, the Lhasa Apso, the Tibetan terrier, is more a product of evolution rather than human influence. Of the five recognized Tibetan breeds; the Tibetan Terrier, Tibetan Spaniel, Do-Khyi (Tibetan Mastiff), Lhasa Apso and Shih Tzu, the Lhasa is the one breed most directly influenced by the harsh Himalayan-Tibetan climate conditions.
There are many reasons why this happened. Firstly, the Tibetans only began to selectively breed the Lhasas around 800-years ago in the city of Lhasa, capital city and home to the Dalai Lamas. However, the breed traces its origins some 2,000 years ago in the Tibetan environment.
Secondly, historians highly speculate whether these Tibetans actually attempted the sophisticated practice of selective breeding that is so popular today. Early Tibetans were hunters and herders who depended on Tibetan dogs to hunt, protect flocks and serve as watchdogs and companions to humans. The natural tendencies of Tibetan breeds, fashioned by evolutionary forces, were more than enough for for ensuring survival tasks faced by the Tibetans.
Thirdly, the physical form of a Lhasa Apso has remained largely unchanged from its original form, because it is still able to conserve heat when necessary. Cold adapted animals have bodies with a higher muscle and fat ratio, in comparison to 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 body's surface area, the more surface there is, the faster heat is lost. Conserving heat is a function of the ratio of body mass in relation to area, the one with the most surface will lose heat more quickly.
Because the body of a Lhasa Apso is shorter and rounded, it has less surface area than a longer-legged, equal in weight, warmer environment cousins. Those same forces also govern body type; people of Eskimo lineage have shorter, stouter bodies and less surface mass than an equally weighted Equatorial person who has a longer, leaner body and a higher surface area. In short, to limit loss of heat in the cold, an animal is better served by a body that is as compact and short-legged 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 stamina, not speed, for walking, jumping and climbing, and not like the bodies of other dog breeds.
This article was written by John Jackson and has been contributed by http://www.greatdogsite.com. For more information on the Lhasa Apso, please visit our page http://www.greatdogsite.com/breeds/details/Lhasa_Apso/.
ไม่มีความคิดเห็น:
แสดงความคิดเห็น