New paleontological and genetic evidence has made us reevaluate the domestication of dogs.
There are over half a billion dogs on the planet(1). There are actors, rescuers, herders, hunters, guides, guardians, watchers, racers, entertainers, detectives and companions just to name a few! Dogs have become so embedded in our culture and in our day-to-day lives that they have earned themselves the role of man’s best friend.
But where did they come from?
Genetic evidence shows that every dog on the planet, from your pet poodle to the pug in “Men in Black”, is descended from the grey wolf (Canis lupis) or from an extinct, very closely related species of wolf (2). But when exactly the first domestic dog diverged from that wolf lineage is another question entirely, which has turned out to be quite difficult to answer.
It had been assumed that domestic dogs arose from wolves scavenging around the edges of early settlements. There would have been selective pressures on the wolves to become tamer and less aggressive in order to grab a quick meal. Eventually, the classic canine head tilt and wagging tail were born. Everyone was happy; humans got extra protection and the wolves/proto-dogs got regular meals.
But, as the first true settlements didn’t appear until humans made the shift from hunter-gatherers to agriculturalists around 10,000 years ago (The Neolithic Revolution), the first domestic dogs couldn’t really have appeared before this time.
So how do you explain this?
These fossil remains more closely resemble domestic dogs than wolves and are over 30,000 years old.
The first image shows the skull of the ‘Goyet dog’. Mietje Germonpre and her colleagues discovered it in the Goyet cave in Belgium. Radiocarbon dating has revealed that it is about 32,000 years old (3). The second image is of the exceptionally well-preserved Altai dog skull found by Nikolai Ovodov and his team. This fossil is 33,000 years old and was found in a cave in the Altai Mountains of Siberia (4).
Why do some experts think these skulls belonged to dogs and not wolves?
There are a number of morphological characteristics of skulls that are used to differentiate between wolves and dogs. When compared to wolves, dogs show a widening and shortening of the skull, a general crowding of the teeth and a reduction in brain size. These neotenic traits show a trend towards the juvenile state of wolves.
The Goyet dog and the Altai dog don’t stand alone. A number of other recently discovered fossil canids found across Europe and Asia also appear to be more dog than wolf. What is remarkable about these EP (European Paleolithic) dogs is that they have been dated to between 19,000 and 26,000 years ago – well before agriculturalist times. It has even been suggested that some of these EP dogs were buried by humans (5). In 2013, a fascinating study on the mitochondrial DNA of dogs and wolves (with living and fossil subjects – including the Goyet dog and other EP dogs) revealed that domestication took place between 18,800 and 32,100 years ago (6).
The Goyet dog, Altai dog and other EP dogs, as well as the mitochondrial DNA studies, are complete game changers! All of this evidence certainly points towards domestication of dogs taking place during hunter-gatherer times.
So with the old theory on the domestication of dogs thrown out the window scientists have had to completely rethink the mechanisms of the domestication process. If domestic dogs didn’t arise from curious wolves around the edges of settlements then what was the cause or the reason behind their domestication?
Pat Shipman, retired professor of anthropology at Pennsylvanian State University, has recently published a book giving her views on how dogs were first domesticated. Her book, “The Invaders”, combines invasive biology and archaeology to explain how Homo sapiens and wolves hunted together to take down large prey such as mammoths. She even goes as far as suggesting that this early domestication was one of the driving forces behind the extinction of one of our closest relatives, Homo neanderthalensis (7).
Shipman describes how both of these persistence hunters (wolves and humans) would have benefited from hunting together. Humans would have used missiles such as spears to wound prey. Wolves would then have gone in and carried out the most dangerous part of the hunt – the actual killing of the wounded animal. This would have reduced human casualties from hunts and would have provided more food for the wolves by making the hunting process more efficient. There is even evidence of ‘mammoth megasites’ where absurd numbers of mammoth fossils have been found. The bones at these megasites show evidence of abrasion from teeth and from man-made tools.
Shipman calls the canids in this partnership ‘wolf-dogs’. She says that they are not similar to modern domestic dogs or to modern wolves but that they are not similar to ancestral wolves either.
There is criticism of Shipman’s theory. Other researchers have described how it is unlikely that wolves in a ‘feeding frenzy’ would share food with humans. Equally, humans were already top predators and effective hunters who probably didn’t need any help from wolves.
Finding the exact time and place of the domestication event of dogs is almost impossible for a number of reasons. Firstly fossils are rare – and the fossils that we do have are sometimes not preserved very well. Secondly, the genome of domestic dogs is a bit of a mess. Domestic dogs and wild canid species can interbreed and this complicates matters. As well as that there is the problem of “the giant whirlwind blender of the European crazy Victorian dog-breeding frenzy”, as Greger Larson called it (5). Another very interesting reason why understanding the domestication of dogs is difficult is that there could have been more than one domestication event. Charles Darwin speculated this when he suggested that dogs may have evolved from a number of wild ancestors. Dogs could have been domesticated many times in many different places. The genetic evidence certainly implies that there was more than one event (2). Perhaps the Goyet and Altai dogs were from a group of domesticated wolf-dogs that went extinct.
A recent international collaboration could shed light on the subject of dog domestication. Up until now very little work has been done on the nuclear DNA of dogs and wolves and their ancestors. This is due to the lack of data – extracting nuclear DNA from fossils can be very difficult and can cause considerable damage to the fossils themselves.
However, Greger Larson from Oxford University has created an international super group of canine genetics specialists (8). Their work started in 2013 and is due to be complete later this year. They hope that the nuclear DNA that this huge study has obtained will answer the big questions on dog domestication – when, where and how many times. The canine scientific world awaits with baited breath as publications based on this nuclear DNA dataset are due to appear later this year.
One thing is for sure – the results will almost certainly give us a date that comes well before agricultural times. Not only could this have serious implications for the evolution of dogs but it may also reveal some interesting facts about the migration and evolution of man.
Title image credits: Ghost Bear Photography. (Check them out!)
2 = Thalmann, O. et al. “Complete Mitochondrial Genomes Of Ancient Canids Suggest A European Origin Of Domestic Dogs”. Science 342.6160 (2013): 871-874. Web.
3 = Germonpré, Mietje et al. “Fossil Dogs And Wolves From Palaeolithic Sites In Belgium, The Ukraine And Russia: Osteometry, Ancient DNA And Stable Isotopes”. Journal of Archaeological Science 36.2 (2009): 473-490. Web.
4 = Ovodov, Nikolai D. et al. “A 33,000-Year-Old Incipient Dog From The Altai Mountains Of Siberia: Evidence Of The Earliest Domestication Disrupted By The Last Glacial Maximum”. PLoS ONE 6.7 (2011): e22821. Web.
6 = Thalmann, O. et al. “Complete Mitochondrial Genomes Of Ancient Canids Suggest A European Origin Of Domestic Dogs”. Science 342.6160 (2013): 871-874. Web.
7 = Shipman, Pat. The Invaders. Print.