Since the 1990s, this view has been left behind. What used to be a disadvantage has become today the great differential of the works with dogs. After all, this is the only animal species, besides the cat, that has evolved alongside man. Its natural niche is nowadays the same as the human being’s. Nobody knows for sure when its process of domestication occurred, an event that probably took place in Asia between 15 thousand and 100 thousand years back (the data is uncertain and debatable).
This change of view about the inclusion of Canis familiaris in the world has increased tenfold the quantity of scientific articles about the behavior of the species in the last few years. One of the recent articles that had most repercussion, in the media outlets as well, was an article published in June 2004 in the famous American magazine Science by researchers from the Max Planck Institute for Evolutionary Anthropology, in Leipzig.
In the study, the team of German researchers described the cognitive skills of Rico, a border collie, a breed with a reputation for being intelligent. Targeted for extensive training, the dog, then 9 years old, had mastered a vast “vocabulary”: his trainer would say one of the 200 words known by the dog, and the dog would fetch the object or toy designated by the human voice. Rico was also capable of associating a new word to a new object. This form of learning, called technically fast mapping, is comparable to the way that 2 or 3-year old children incorporate terms into their repertory.
Few people doubt nowadays that there is much to be learnt with dogs, not only in the area of the comprehension and production of communicative signals, but also in the field of studies in comparative genetics (see the article below about the sequencing of the genome of man’s best friend). “The greatest challenge today is to understand the limits of the skills of dogs and how they, with a cognitive system that is probably simpler than ours, can ‘simulate’ behaviors to interact with humans”, says ethologist Ádam Miklósi, from Eötvös University, in Hungary, one of the great scholars of the theme. Like his colleague Cesar Ades, from USP, Miklósi belongs to the lineage of ethologists for whom the dog’s capacity for communication with man was a decisive element in its process of domestication. He argues that dogs are good at perceiving visual signs and clues given by humans, not because they have enormous mental skills, but rather because they are more interested in us. “Dogs direct their gaze to the human being as no wolf does”, comments Ades. This perhaps explains why the dog, and not its wild relative, has become man’s best friend.
Science has found one more function for the dog: besides being man’s best friend, Canis familiaris may be an excellent genetic model for studying, and who knows, for finding, the molecular bases that led to the occurrence of a series of diseases in human beings, such as cancer and another 350 disorders present in mammals. In the long term, this may be the greatest contribution of the publication of the practically complete (99%) sequencing of the genome of the dog in the issue of December 8 last year of the British magazine, Nature. The main genetic material used in the work came from Tasha, a 12-year old boxer, who was selected by breeders’ associations and veterinary colleges for representing a very pure breed, with very homogeneous DNA and fewer differences amongst its pairs of chromosomes. This peculiarity made the task of sequencing the animal’s genome quicker. For being centered on the DNA of a bitch, the work does not bring information about the canine Y chromosome, present only in animals of the male sex.
Written by an international group of researchers, led by Kerstin Lindblad-Toh, from the Broad Institute, of the United States, the article in Nature informs that the 39 pairs of chromosomes of the dog’s genome have 2.4 billion pairs of nitrogenous bases, the chemical units that make up the DNA, and house 19,300 genes. Man has 23 pairs of chromosomes, about 3 billion base pairs and roughly 26 thousand genes. The smaller size of the canine DNA in relation to the DNA of our species is due to the existence of fewer repeated sequences in its genome. Besides Tasha’s genetic material, the study also contains data about the genome of another ten breeds of dogs and wild relatives of the dog (like the wolf and the fox), a kind of molecular information that will be very useful for establishing connections between the activation of genes and the appearance of specific physical traits and the development of the most common health problems in these animals. “Hundreds of years of careful crossbreeding have created the present-day breeds, which are an excellent genetic model for human diseases”, says Hans Ellegren, from the Evolutionary Biology Center of the University of Uppsala, in Sweden.
With the genetic sequencing of the dog in their hands, the researchers were able to make some comparisons with the genomes already mapped of other species of mammals. In a first study with this approach, they discovered that about 5% of the human genome seems to be conserved in the dog, and also in the mouse, an indication that these stretches must be essential for the three animals. The article on Tasha’s DNA is not the first effort to sequence the genome of the dog. In 2003, in a work published in the American magazine Science, another team of scientists mapped 75% of the genetic material of Shadow, the poodle of Craig Venter, the American scientist-businessman who set up a private program for sequencing the human genome. Both the canine genomes, Tasha’s and Shadow’s, are useful for science, but the boxer’s sequence is more complete and refined.
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