The Siamese cat is one of the first distinctly recognized breeds of Asian cat. The Siamese became one of the most popular breeds in Europe and North America in the 19th century. In the 1950s–1960s, many breeders and cat show judges began to favor the more slender look. As a result of generations of selective breeding, they created increasingly long, fine-boned, narrow-headed cats; eventually the modern show Siamese was bred to be extremely elongated, with a lean, tubular body, long, slender legs, a very long, very thin tail that tapers gradually into a point and a long, wedge-shaped head topped by extremely large, wide-set ears.
The carefully refined modern Siamese is characterized by blue almond-shaped eyes; a triangular head shape; large ears; an elongated, slender, and muscular body; and point coloration. (Aside from the coloration, it bears little resemblance to the original stock, and the more moderate, traditional or "old-style" Siamese, with a much rounder head and body, has been re-established by multiple registries as the Thai cat.)
By the mid-1980s, cats of the original style had largely disappeared from cat shows, but a few breeders, particularly in the UK, continued to breed and register them, resulting in today's two types of Siamese: the modern, "show-style", standardized Siamese, and the "Traditional Siamese", both descended from the same distant ancestors, but with few or no recent ancestors in common, and effectively forming distinct sub-breeds, with some pressure to separate them entirely. In addition to the modern Siamese breed category, The International Cat Association (TICA) and the World Cat Federation (WCF) now accept Siamese cats of the less extreme type under the new breed name Thai. Other, mostly unofficial, names for the traditional variety are "Old-style Siamese", "Classic Siamese", and "Applehead" (originally a derogatory nickname coined by breeders of modern-type Siamese).
The modern Siamese shares the pointed color pattern with the Thai, or traditional Siamese, but they differ in head and body type. The pointed pattern is a form of partial albinism, resulting from a mutation in tyrosinase, an enzyme involved in melanin production. The mutated tyrosinase enzyme is heat-sensitive; it fails to work at normal body temperatures, but becomes active in cooler (< 33 °C) areas of the skin. This results in dark coloration in the coolest parts of the cat's body, including the extremities and the face, which is cooled by the passage of air through the sinuses.
All Siamese kittens, although pure cream or white at birth, develop visible points in the first few months of life in colder parts of their body. By the time a kitten is four weeks old, the points should be sufficiently clearly distinguishable to recognize which color they are. Siamese cats tend to darken with age, and generally, adult Siamese living in warm climates have lighter coats than those in cool climates.
Originally the vast majority of Siamese had seal (extremely dark brown, almost black) points, but occasionally Siamese were born with "blue" (a cool grey) points, genetically a dilution of seal point; chocolate (lighter brown) points, a genetic variation of seal point; or lilac (pale warm gray) points, genetically a diluted chocolate. These colors were at first considered "inferior" seal points, and were not qualified for showing or breeding. All of these shades were eventually accepted by the breed associations, and became more common through breeding programs specifically aimed at producing these colors. Later, outcrosses with other breeds developed Siamese-mix cats with points in other cat colors and patterns, including Red and Cream point, lynx (tabby) point, and tortoise-shell("tortie") point.
In the United Kingdom, all pointed Siamese-style cats are considered part of the Siamese breed. In the United States, a major cat registry, the Cat Fanciers' Association, considers only the four original fur colors as Siamese: seal point, blue point, chocolate point, and lilac point. Oriental Shorthair cats with color points in colors or patterns aside from these four are considered color point Short hairs in that registry. The World Cat Federation has also adopted this classification, treating the color point Short hair as a distinct breed.
