INTRODUCTION
Derived from the wolf domestication since more than 100,000 years(1), the dog is the living being more attached to our species and, with the pass of the time a living being that little by little has stopped being just a biologic entity to transform into a cultural product. In ancient civilizations, for example the one that developed in Mexican territory, the dog was involved inside of this full biological-cultural duality so the studies of Canis familiaris history inside the pre-Hispanic Mexico turns itself into an indispensable and interesting theme for a lot of Mexicans.
ANTECEDENTS
In Mexico the ancient manifestations related with the dog had always been diverse and abundant(2) but until 1988 there was any effort that let someone study them in a scientific form. In that same year the authors joined their efforts to advance in this field, commitment that has existed during the pass 16 years, giving as a result a lot of information and proposals that let, until this moment, to know the pre-Columbian dog's history in a level such as the one about dogs in any culture in the world.
To reach this objective an interdisciplinary work group was created. Many investigators of different areas had participated inside of it, in a continuous or temporal way: Alicia Blanco, Bernardo Rodrígueza and Raul Valadez have in their charge the information about archaeozoology and ethnozoology, Katiuska Olmos and Fernando Viniegrab the information about veterinary medicine and Samuel Tejedac and Roberto Rodríguezd had collaborated in the biochemical and physical-chemistry studies.
The information available in this moment about the Pre-Columbian Mexico dog start from many sources: archaeozoological remains, iconographic representations, ethnohistorical sources, medic-veterinary information, Mexican hairless dogs breeders´ information, actual ethnologic information, such as many packages of information related with genetic, biochemical, physical-chemistry, cellular biology and molecular biology.
RESULTS
The dog remains in Mexican archaeological sites are always abundant, being the 20% of the total identified individuals. The materials include from bony fragments to complete skeletons, including manufactured pieces. The bones can be found without handling evidence; with human or another animal bites signs, with cut marks which show manufacture activities or cutting work, we can see pieces with a high level of manipulation to the point in which we can identify these ones as tools with evidence of close contact with direct fire and high heat.
The sites in which the dog bones remains appear are mainly domestic trash places, burials and as part of offerings related with ritual activities. With this information is possible to join the presence of the dog inside a pre-Hispanic environment with feeding activities; these bones with the making of tools and instruments; parts of individuals in some people's clothes or for some specific event; cooked pieces were put in burials as offerings for the deceased; complete or partial individuals were offerings in many ritual acts, complete sacrificed animals collocated in graves were part of ceremonial events and complete dogs were put with the deceased for them to serve as guides.
The bones remains had let us recognize until 2004 the presence of many pre-Hispanic times types of dogs, which are identified through the dentition, the skull form and the size of the members (2,4-7). The variety recognized are the common Mesoamerican dog, the hairless dog or xoloitzcuintle, the tlalchichi or short legged dog and the Mayan dog. The associated contexts of these discoveries do not show direct association between types and human activities.
Beside all this varieties, it has been proved the use of the dog to form hybrids with the wild canids (coyotes and wolves). The hybrids of wolf and dog are, for much, the more abundant, because appear since the III century A.D. in Teotihuacan and its presence has been recognized in many human settlings until the XV century A.D. in Tenochtitlan. Its identification is based in the dentition, which has intermediate size between dogs and wolves, furthermore its body dimensions, a lot more large than the first's ones. The associated contexts suggest its use with ceremonial purposes and as military symbols.
Studies related with the quantification of trace elements (strontium and zinc) in bony tissue of pre-Hispanic dogs of the center of Mexico(11) show that its diet had a huge variety, since animals with vegetable diet, until others in which meat was the base of its feeding. In some specific cases, the ones in which it were related with ritual activities had results that were coherent with the idea that it were fed in a special way.
In the iconography, the common dog (ceramic, lithic, codex). Its representations appear as part of offerings left to the dead or associated to some specific ritual acts. We can see representations in mud which simple elaboration or the presence of specific details (as wheels) suggest its use as toys. In some codex(12,13) it is associated as divines or religious elements that are related with the solar cycle, the lightning, water, rain, corn of the death world. In the Aztec calendar (XIV-XVI centuries A.D.) the dog appear as the 10th sign of the days, and its regent god was Mictlantecutli, Lord of the Dead.
The written books in the XVI century, in the beginning of the Colony time, put the dog as an animal very related with the human activities. Its use is told as a meat source(13-17) mainly in the gods´ Parties; they were used as a sacrifice animal in the parties of the beginning of the year(7,16), in the asking of rain to the gods(17) and in some funerary practices in which these dogs were included with the deceased so it can be his company in this journey to the other world(13). This universe of uses began the existence of markets(15) in which dogs were sold depending in the people's needs. These same books put the dog as a very close animal to man and it was easy to found many types, being a very close relationship between the description of very different forms, its names and archaeozoological data.(2,18).
The studies in molecular biology show that the dog has its origin in Asia and that it came to Mexico as a domestic animal(18). The DNA obtaining of archaeozoological Mexican samples let us see that the different kind of dogs registered to this moment come from different genetic lines.
DISCUSSION
The results obtained about the origin of the dog and its arrival to America makes doable the idea that the occupation of the continent was made from groups of Homo sapiens and Canis familiaris, so all the human history in this continent was made with a dog at their side. No less than 8,000 years ago the dog arrived to Mexican territory and the firsts evidences are individuals that were put beside deceased ones and representations in mud, that only proves important symbolic elements associated with the dog since the earlier times and therefore its material and ritual use were always an important thing inside the dog history in the pre-Hispanic Mexico
For us to understand the symbolic relation associated with this animal we considered necessary to begin with three concrete and visible points for the pre-Hispanic man: its value as companion and protector, its reproductive cycle and its use as meat source (Figure 1). About the first point, the close relationship dog-human made the idea that this interaction had to grow more beyond the earthly world and be an option even to the dead, concept that made a direct association with the concept "death" and with that its presence in traditions about the other world.
The relation that we see about the dog and the rain, the lightning and the agriculture doesn't seem to have logic with the dog as a biological entity, but this can be explained when we watch the reproductive cycles, the corn cultive cycle and the rain annual cycle in Mexico. In this part of the world the dog that lives by his own in the outside has a reproductive cycle of six months in which it come in to heat in the final days of February and ends at the firsts ones of April (fist period) and in the last days of August to the first ones of October (second period), with the birth of the puppies between May and June or between November and December. The rhythm of this process matches with the corn cultive cycle, because the period of cultive begins with the first rain, sometimes since April, with the most human effort in May and June and in the period of harvest in November.
In the other hand, the rain annual cycle, in most part of Mexico begins in April, when the dogs are in the final phase of heat (in its first reproductive period), so this dog activities will be, for a pre-Hispanic individual, as a prelude of the rain arrival and the moment to start to plan the corn seed. At last, the arrival of the puppies in the two reproductive periods would be at the same time of the last seed activities and the beginning of the harvest, all this couldn't be an unimportant thing to this people, therefore the use of the puppies in rain parties and its association with fertility.
The use of the dog's flesh as food was always a normal activity, just as the remains shows us, but based on the past information we can see how the use of its flesh was strictly attached with the rain and agriculture gods, from there that its continuous consume took place in the parties and funerary activities days.
We can associate this situation to any kind of dog that lived in pre-Hispanic times, but the hybrids of wolf and dog. In this case, the use of a female dog in ceil just to have puppies that people could handle but searching that the wild blood of its wild father remained made a more continuous use of the wolf part, so in this form we can associate this organisms with the warriors, with ceremonial activities offerings of the highest level and with the night.
Furthermore of this religious universe, the evidences also let us know the way in which the dog and man shared their daily coexistence. The presence of bones in domestic trash places and the existence of tools made with these bones show that their use as food, could be done just the same way as with other animals. There were dogs that were fed in a special way and others that depended on themselves, ones that grew a lot of love in their masters and were buried together as if it were resting at its master's feet, but there are legends too that show how with the divine support they took the chance to unload its anger in those men that hit them or denied them food (19).
The information about the breeders existence let us conclude that in the pre-Hispanic world there was a huge knowledge about handling dogs with productive purposes, and although we don't know how much the phenotype selection for the creation of forms with predetermined uses were used, being the unique documented case until this moment about this hybrid creations.
In this moment it is considered true that the different groups of dogs that arrived to Mexican territory possessed a non-specialized morphology, although they had the predisposition to certain modifications in their genes, the same that later gave place to known types. The "common type" dogs, without any doubt would be later its direct offspring, animals which genetic constitution was free of mutations that could change their physic condition.
The hairless dogs or "xoloitzcuintles" appear in the west Mexican territory two thousand years ago, just after a genetic syndrome (ectodermic dysplasia)(2). Five centuries later its dispersion began, first to the center and south, then to the southeast, always as part of the human migratory movements. Its dissemination and persistence in the pass of the centuries depended mainly in their ectodermic dysplasia dominant condition; we know this because their dentition characteristics indicate that few times a "pure line" creation was searched.
The short legged dogs, or "tlalchichis", had its origin in the west too, for achondroplasia. Apparently its non-dominant condition mutation limited them to disperse, because its presence has only been recognize in the Center of Mexico. Finally, in the southwest of Mexico a short faced dog or Mayan dog existed, it was the smallest and skinny one with a lighter and brachycephalic cranium. This animal could been just a variation of the common dog or its characteristics were an isolation result that existed between human populations of the southeast with the rest of pre-Columbian Mexico, because we only know it inside the Mayan area, geographic-cultural region, in which the tropical jungle and the dominance of this culture limited human travels in both directions.
CONCLUSIONS
Accumulated studies in 15 years let us have in this moment a clear view about the dog inside the civilization that developed in the pre-Columbian Mexico, most of all in the center. Although we don't know how much the people created interests about the methodic handling of individuals and its offspring, that didn't impede that diverse kind of dogs appeared, those which the people recognized, used and sep until the European breeds arrival. The study of this part of the pre-Hispanic dog history is a main objective of the authors, because from this appear the need of knowing how many of this forms still exist in our days.
Present in the pre-Hispanic man historic memory, their arrival to the continent with dogs made inconceivable the human existence without this animal at their side, because it had as much value as hunting partner or as meat source. Circumstances that favored not only its presence in the whole region human community, but as an element that had to be in funerary activities just as much to join symbolically with death. Other circumstances drove to the association of the dog with the agriculture and rain cycle, condition that joined with the last one drove in a very strong symbolic charge. All this let us conclude that its religious value went to a level that very few times could be repeated in the ancient World, although this didn't impede it to be used and seen as a domestic animal in the earthly world and that its existence depended totally in humans.
| Figure 1. | 
Symbolic associations map attached to the dog use as main part its use as food, as company and protection and about its reproductive cycle (capital letters inside squares). The concepts in bold letter are elements in which the dog was considered as a symbol. |
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Endnotes
a. Paleozoology Laboratory, Instituto de Investigaciones Antropológicas de la UNAM
b. Centro Médico Nacional "20 de Noviembre", Servicio de Bioterio, ISSSTE.
c. Instituto Nacional de Investigaciones Nucleares
d. Arqueometry Laboratory, Universidad de la Habana, Cuba.
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