Source: Matheus Bertelli/Pexels
How long have dogs and humans lived together? A piece of an ancient leg bone is causing scientists to reconsider just when humans domesticated dogs. The Human Evolutionary Biology team at the University of the Basque Country (UPV/EHU) in Spain, led by Professor Conchi de la Rúa, has recently reanalyzed a canine humerus bone that was recovered from a cave in the northern part of Spain in 1985. It suggests that dogs may have been domesticated as early as 17,000 years ago in Europe.
It is clear that dogs diverged from wolves because we humans began to domesticate them; however, the questions of how, where, and when have been very sticky issues among scientists. Different research techniques have given widely different answers, so current studies try to employ multiple methods to see if they all converge on the same answer.
The most ancient domesticated dog in Europe?
Source: Hervella et al., J. Archaeol. Sci. Rep., 2022, press release
When Did This Ancient Dog Live?
The task of identifying biological remains is not easy. Tracing the earliest dogs involves two stages, first identifying the fossil remains as actually being dogs (not wolves or some other form of wild canine) and second identifying the specific time that that animal existed.
To reanalyze this bone, researchers used radiocarbon dating to determine its age. The most common form of carbon found in living organisms is C-12. However, a small amount of an alternative radioactive form of carbon form called C-14 is continually formed in the upper atmosphere through the effect of cosmic rays. It then combines with oxygen to form carbon dioxide, which enters plants and animals through photosynthesis and the food chain.
When an animal dies, it stops absorbing C-14. The interesting aspect of C-14 is that this form of carbon is unstable, and it begins to decay over time. Measuring the amount of C-14 left in a bone gives an estimate as to how long it has been since the animal died.
There are certain limitations associated with radiocarbon dating. First of all, it doesn’t work for very old samples (maybe around 60,000 years ago). Secondly, it is destructive. In addition to various pre-treatments, a portion of the fossil must be burned and converted to a form suitable for use by the analysis equipment. In other words, the process of dating actually eradicates part of the sample. In 1985, when this bone was originally collected, the amount of material needed for C-14 dating was quite large and would have destroyed much of this rare item. However, the techniques have improved since then, and the fossil can now be dated using only a few milligrams of bone scraping.
Can We Be Sure That This Was Really a Dog?
Identifying the species that the bone came from is difficult. The process starts with analyzing the shape of the bone. With canines, this isn’t necessarily reliable. Wolves may have had a greater variety of body shapes in the past, and there are certainly regional differences in the size of wolves. Thus, scientists have to contend with bones that have dog-like and wolf-like characteristics, which appear in those fossils dated between 15,000 and 40,000 years ago. This particular bone fragment looks very similar to more recent bones, which have been conclusively identified as dogs. But further confirmation was required.
The trail of the early dog is faint, and part of it is written in the genetic makeup of the species. Unfortunately, the passage of time ravages DNA. Therefore the DNA that geneticists use for such studies is not the material that we think of as genes (which is found in the chromosomes in the nucleus of cells). Half of that nuclear DNA comes from the mother and half from the father. The nuclear DNA is unique to each individual because the genetic material from each parent is a chance selection of half of that parent’s chromosomes. This makes the DNA of the offspring different for each mating.
However, the DNA that helps us trace the origin of dogs is not found in the nucleus of the cell with the chromosomes, but it is found in the mitochondria (tiny oval organs that float around in each cell and have the job of converting nutrients into energy). What is special about mitochondrial DNA is that it comes only from the mother. Geneticists are fascinated by mitochondrial DNA because they believe that we can use it to get a genetic picture of the “first mother” for any species. In theory, mitochondrial DNA can be used to trace a simple line of descent from female to female to female back to the beginning.
Fortunately, mitochondrial DNA is somewhat more robust than nuclear DNA and can be recovered from bones. Still, as in the case of radiocarbon dating, it requires the destruction of part of the sample. However, as in the case of radiocarbon dating, recent advances in measurement techniques make it possible to use only a tiny bit of material that can be recovered with a dental drill.
Analysis of the mitochondrial DNA from this bone confirms that it is virtually identical to the mitochondrial DNA found in known dogs that lived thousands of years later.
Does This Change the Way We Think About the Domestication of Dogs?
The usual consensus among scientists is that dogs were domesticated around 14,000 years ago since that appears to be what we typically find in European and Asian fossils. The interesting thing is that the bone from the Basque cave has a carbon dating which indicates that this dog died around 17,000 years ago. That means that the appearance of domesticated dogs in Europe might be 3,000 years earlier than we originally believed.
There have been older findings of domesticated dogs in Asia. Up until this recent research, what appeared to be the earliest unambiguous fossil evidence of domesticated dogs was recovered from the Bryansk Region in the Central Russian plain, roughly 400 miles southeast of Moscow. Based on the radiocarbon dating of two skulls found there, domesticated dogs may be as old as 17,000 years. Previously to this current report, no findings dated as being that old had been found in Europe.
If the bone from the Basque cave has a carbon dating in about the same time range as the Bryansk fossils (namely around 17,000 years ago), it opens up a bit of a new puzzle. How can it be that we find such early domestication of dogs in Russia, and in nearly the same time frame, we find what appears to be similar early evidence of domestication of a dog 2,400 miles (3,900 km) away in Europe? Given the fact that rapid means of transportation were not available in the Paleolithic Era, this research might confirm the suggestion of another research team headed by Anders Bergström of the Francis Crick Institute in London, which suggested that the domestication of dogs may have occurred in more than one place and may even have involved different varieties of wolves.
In any event, it appears that dogs have been with us for a long time and are clearly the first species of animal that humans ever domesticated.
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