Physical characteristics
Despite
their close genetic relationship and the ability to inter-breed, there are a
number of diagnostic features to distinguish the gray wolves from domestic
dogs. Domesticated dogs are clearly distinguishable from wolves by starch gel
electrophoresis of red blood cell acid phosphatase. The tympanic bullae are
large, convex and almost spherical in gray wolves, while the bullae of dogs are
smaller, compressed and slightly crumpled. Compared with equally sized wolves,
dogs tend to have 20% smaller skulls and 30% smaller brains.:35 The teeth of
gray wolves are also proportionately larger than those of dogs. Dogs have a
more domed forehead and a distinctive "stop" between forehead and
nose. The temporalis muscle that closes the jaws is more robust in wolves.:p158
Wolves do not have dewclaws on their back legs, unless there has been admixture
with dogs that had them. Most dogs lack a functioning pre-caudal gland and
enter estrus twice yearly, unlike gray wolves which only do so once a year.
So-called primitive dogs such as Dingoes and Basenjis retain the yearly estrus
cycle. Dogs generally have brown eyes and wolves almost always have amber or
light colored eyes. The skin of domestic dogs tends to be thicker than that of
wolves, with some Inuit tribes favoring the former for use as clothing due to
its greater resistance to wear and tear in harsh weather. The paws of a dog are
half the size of those of a wolf, and their tails tend to curl upwards, another
trait not found in wolves The dog has developed into hundreds of varied breeds,
and shows more behavioral and morphological variation than any other land
mammal. For example, height measured to the withers ranges from a 6 inches (150
mm) in the Chihuahua to 3.3 feet (1.0 m) in the Irish Wolfhound; color varies
from white through grays (usually called "blue") to black, and browns
from light (tan) to dark ("red" or "chocolate") in a wide
variation of patterns; coats can be short or long, coarse-haired to wool-like, straight,
curly, or smooth. It is common for most breeds to shed their coat.
Behavioral differences
Unlike
other domestic species which were primarily selected for production-related
traits, dogs were initially selected for their behaviors. In 2016, a study
found that there were only 11 fixed genes that showed variation between wolves
and dogs. These gene variations were unlikely to have been the result of
natural evolution, and indicate selection on both morphology and behavior
during dog domestication. These genes have been shown to affect the
catecholamine synthesis pathway, with the majority of the genes affecting the
fight-or-flight response (i.e. selection for tameness), and emotional
processing. Dogs generally show reduced fear and aggression compared with
wolves. Some of these genes have been associated with aggression in some dog
breeds, indicating their importance in both the initial domestication and then
later in breed formation.
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