September 23, 2010
Over the years humans have manipulated the canine species through selective breeding to create a wide variety of different breeds. The ancestor of all of these breeds is the grey wolf, which was domesticated and bred over and over to create different shapes, sizes, coats, dispositions, etc. In a study done by Michael Valenzuala, a variety of dogs were examined to see if the effects of selective breeding to create new breeds has altered the way the dogs brain develops and thus altering behaviour. There are two main classification of dogs that Valenzuala examined; short-snouted and long-snouted. Naturally, a dogs snout is long, as is the snout of a wolf . However, many breeds exist today that exhibit shorter or longer snouts than would be found in the natural world. Breeds such as pugs, have extremally short snouts while other species such as greyhounds, exhibit longer snouts than one would expect to naturally occur. Through the skull measurements and MRI scans of 13 specimens, Valenzuala and his team studied positioning of the ceribral hemesphere and the olfactory bulb, which is responsible for the dogs sense of smell.
The primary source of this study, Human Rotation and Reorganization of the Brain of Domestic Dogs, describes in detail Michael Valenzualas' study, focusing mostly on the length of the skull directly affecting the reorganization of the dogs' brain. He made the conclusion that through selective breeding, we have shortened the snout of the dog to the point where its behaviour and sense of smell may be comprimised/ affected. The primary source goes into great depth describing the methods in which he made these conclusions. Although he did not have a large number of specimens to study (11 recently euthanized dogs, 2 live specimens), he made sure to have a wide variety of species with snouts ranging from short to long. He measured the lengths and widths of each skull so it could be directly related to the amount of room within for the brain to develop. He also preformed MRI scans to locate the positioning of the ceribral hemispheres of the brain. Through this he was able to make the conclusion that the brain grew in a different way in shorter-snouted dogs, where space was more limited.
In the secondary source, Farris Jabr was quite accurate in presenting this study in his own words. He portrayed the main reason why this study was conducted and the final conclusions so that the reader could understand. Jabr was able to put the findings of Valenzualas' work into word that were much easier to read, while still keeping the main components of the original text. However, the secondary source incorrectly made the assumption of which breeds were used in the experiments. Jabr describes that dogs such as an akita and a mastiff were amoung the speciments that Valenzuala aquired from a nearby pound, while the only breeds that were descibed in the original text were the two live english springer spaniels.
Another difference between the primary and secondary source was the emphasis on the impact of the brain rotation on behaviour and senses. The primary source goes into great detail descibing the that as a result of shorter snouts, the dogs had a rotated cerebral hemesphere and that the olfactory bulb was closer to the base of the skull. Valenzuala made the suggestion, although stated that it was still unproved, that the reason shorter snouted dogs were never used as tracking dogs was because of this. If the olfactory bulb is comprimised, it could affect the dogs sense of smell. In the secondary source, Jabr makes the the suggestion that snount size determines behaviour/ scent ability of the dog, a main point of his article.
Valenzuala was able to make the conclusion that the length of the snout of the dog directly determined the rotation of the brain and the way it grew, despite the size and weight of the dog. The width of the snout didnt seem to affect the results of this experiment either. The next stage of this research would be to determine whether or not the rearrangement of the brain negatively affects the dog. The cerebral hemesphere is responsible for alot of the dogs behaviour and if it grows differently, one could assum that the dog would have a different disposition than dogs with normally arranged brains. The placement of the olfactory bulb also may affect the dogs sense of smell, but has not yet been proven.
Overall, the secondary source quite accuratly portrayed the main points of the original study, with a few minor misunderstandings. The reader can understand the experiment through both papers and the point of the experiment is clear in both.