Taste is a very old sense in
evolutionary terms. It
evolved from direct
interactions of the first living
things with the giant bowl of
chemical soup in which they
were immersed. The
substances that were
suspended or dissolved in
water were important to the
survival of these primitive
living things. Some
substances provided food,
some gave warning, and
some could cause damage
or even kill. As animals
evolved, the taste system became more specialized and
sophisticated. Sensations of pleasure and disgust provided by
taste serve a survival function. A reasonable rule of thumb, at
least for natural substances, is that bad tastes are a signal that
the animal has encountered something that is harmful,
indigestible, or poisonous, while good tastes signal useful,
digestible substances.

Because it is important for survival, it is not surprising to find
that taste is one of the earliest senses to begin functioning in
dogs. Young puppies seem to have only their sense of touch,
taste and smell working at birth but the taste sense still requires
a few weeks to completely mature and sharpen.


As in the case of humans, the dog's sense of taste depends
upon special receptors called "taste buds". These are found in
small bumps on the top surface of the tongue called "papillae."
There are some taste buds in other places as well, such as the
soft part of the roof of the mouth (the "palate" and the back part
of the mouth were the throat begins (the "epiglottis" and the
"pharynx". An animal's taste sensitivity depends upon the
number and type of taste buds that it has, much the same way
that sensitivity for smell depends upon the number of olfactory
receptors . Humans win the sensitivity contest for taste, with
around 9000 taste buds as compared with only 1700 for the dog , but
dogs have considerably more taste buds than cats, which
average only about 470.


Specific taste buds appear to be tuned to specific chemical
groups and produce recognizable tastes. Traditionally, when
talking about human tastes, we have identified four basic taste
sensations. These correspond to the tastes that we call sweet,
salty, sour and bitter. Early research did show that the taste
receptors of dogs responded to the same kind of chemicals that
trigger human taste sensations. There was one clear difference,
however, and that has to do with the taste of salt. Humans, and
many other mammals, have a strong taste response to salt. We
seek it out, and like it on our food. Pretzels, potato chips, and
popcorn, for example, are snack foods that are usually liberally
dosed with salt. Salt is needed to balance our diet and there is
not much of it to be found in vegetables and grains. Dogs,
however, are primarily carnivores and in the wild, most of their
food is meat. Because of the high sodium content in meat, the
wild ancestors of dogs already had a sufficient amount of salt in
their diet and did not develop our highly tuned salt receptors and
the strong craving for salt.

Dogs, are not exclusively carnivorous, but are usually classified
as omnivores, meaning that they eat, not only meat, but plant
material as well. Nonetheless, in the wild, more than 80 percent
of a canine's diet will be meat. For this reason, in addition to
sensors for sweet, salt, sour and bitter, dogs also have some
specific taste receptors that are tuned for meats, fats and meat
related chemicals. Dogs will tend to seek out, and clearly prefer
the taste of things that contain meat or flavours extracted from
meat.


The sweet taste buds in dogs respond to a chemical called
furaneol. This chemical is found in many fruits and in tomatoes.
Cats are virtually "taste blind" for this substance. It appears that
dog's do like this flavour, and it probably evolved because in a
natural environment dogs frequently supplement their diet of
small animals with whatever fruits happen to be available.


The taste buds for the basic flavours are not distributed equally
across the tongue. Sweet is best tasted at the front and side
portion of the tongue. The sour and salty taste buds are also on
the sides but further back, with the salt responding area being
rather small. The rear portion of the tongue is most sensitive to
bitter tastes. Sensitivity to meaty tastes is scattered over the top
of the tongue, but mostly found in the front two thirds. However,
all areas of the tongue can respond to all of the taste stimuli if
they are strong enough, it is just that the areas that I mentioned
are noticeably more sensitive.


Because of dogs' dislike of bitter tastes, various sprays, and gels
have been designed to keep dogs from chewing on furniture or
other objects. These compounds often contain such bitter
substances as alum or various substances derived from hot
peppers. Coating items with such bitter tasting material will
eventually keep most dogs from chewing on them, but the key
word is eventually. Part of the problem is that the taste buds that
sense bitter are located on the rearmost third of the tongue. This
means that a quick lick or a fast gulp will not register the bitter
taste. Only prolonged chewing will let the bitter work its way
back to where it can be tasted.


Dogs also have taste buds that are tuned for water, which is
something they share with cats and other carnivores, but is not
found in humans. This taste sense is found at the tip of the
dog's tongue, which the part of the tongue that he curls to lap
water. This area responds to water at all times but when the dog
has eaten salty or sugary foods the sensitivity to the taste of
water increases. The guess is that this ability to taste water
evolved as a way for the body to keep internal fluids in balance
after the animal has eaten things that will either result in more
urine being passed, or will require more water to adequately
process. This is useful since dogs are carnivores, and as we
already mentioned, there is a high salt content in meat. It
certainly appears that when these special water taste buds are
active, dogs seem to get an extra pleasure out of drinking water,
and will drink copious amounts of it.




WRITTEN BY:
Stanley Coren: is the author of many books including: Born to
Bark, The Modern Dog, Why Do Dogs Have Wet Noses? The
Pawprints of History, How Dogs Think, How To Speak Dog, Why
We Love the Dogs We Do, What Do Dogs Know? The Intelligence
of Dogs, Why Does My Dog Act That Way? Understanding Dogs
for Dummies, Sleep Thieves, The Left-hander Syndrome


Copyright SC Psychological Enterprises Ltd. May not be reprinted
or reposted without permission