This science article explains how, in prehistoric times, wolves adapted to living with humans before eventually evolving into domestic dogs.
In Human Influence on Natural Selection we learnt how, in more recent times, humans modified the physical appearance of dogs by means of artificial selection.
Without exception all dogs living today are descended from the wolf. (Canis lupus) It was the domestication of wolves in prehistoric times that preceded the evolution of the domestic dog.(Canis lupus familiaris)
We can deduce that the domestication of wolves probably took place more than thirty three thousand years ago. The remains of a 33,000 year old dog found in a remote cave in the Altai mountains of southern Siberia provide conclusive evidence of early evolution of dogs from wolves.
DNA analysis of the bones proves beyond doubt that this animal was more closely related to modern dogs than to wolves.
If the first dogs had already evolved 33 000 years ago then it is highly likely that wolves were first domesticated even earlier -perhaps more than 35 or 36 thousand years ago!
While we know roughly when wolves were first domesticated, we have no way of knowing exactly how this domestication first took place. However we do have some plausible theories…..
One plausibe theory is that humans cared for orphaned wolf pups whose mothers died shortly after giving birth. Perhaps the pups’ mothers had been killed by other predators or had succumbed to disease and illness….
Whatever the reasons, those very young wolf pups reared by humans would have been more easily tamed and socialized.
Once these tame orphaned wolf pups became adults they might have bred with other tame orphaned wolves. More tame wolf pups would have been born…and evolution from tame wolf to domestic dog would have begun!
Another plausible theory of what first led to wolf domestication was that the process was triggered by ‘natural’ selection. It was the wolves themselves that decided to follow their own evolutionary path and become domesticated companions to humans. How could this have happened?
Wolves both hunted prey and scavenged other animals’ kills. They would have been attracted to human settlements by the smell of meat, including the smell of scraps of meat left over from hunting expeditions and the smell of cooked meat wafting into the air from prehistoric cooking pots.
Those ‘more social and less fearful’ wolves which were prepared to take risks by venturing close to human settlements were more likely to have been rewarded with a meal. Wolves would have scavanged scraps of meat and bones from around the campsite, ate food thrown onto middens (rubbish tips) or even been left meals by generous camp dwellers.
Thus the ‘more social and less fearful’ wolves were generally better fed since they now had extra sources of food in addition to the prey they caught on their own hunting expeditions. As one generation followed on from another those more sociable, better fed and healthier wolves produced offspring that were also less frightened of humans.
Thus the ‘flight distance’, how close wolves allow humans to approach before taking fright and running away, reduced over the generations. The newer generations of wolves allowed humans to approach very close before taking fright and running off.
A decreasing ‘flight distance’ is a measure of what we could call increased ‘tameness’. These ‘flight distances’ kept on getting smaller until wolves finally allowed themselves to be patted and stroked by humans.
Contrast the ‘more social and less fearful wolves’ with those ‘less social and more fearful wolves.’ This latter type of wolf was nervous anywhere near humans and would have run away whenever humans got too close. Those ‘less social and more fearful wolves’ never got close enough to humans or their settlements to benefit from this valuable additional source of food. The ‘flight distance’ never decreased over the generations.
Humans began to derive enormous benefits from tame ‘dog-like wolves’ which used to hang around their camps. ‘Dog-like wolves’ improved sanitation by eating scraps of food. ‘Dog-like wolves’ provided warmth and thus helped prehistoric people sleep more comfortably on cold nights.
To this day Aborigines in Australia sleeping in the outback have an expression called the ‘three dog night’. This signifies an exceptionally cold night when humans surround themselves with three dogs to keep themselves warm.
‘Dog-like wolves’ alerted prehistoric villagers to the approach of predators and strangers. Humans used dog-like wolves’ keen sense of smell to track and capture prey.
More than 50 years ago a Russian biologist, Dmitry Konstantinovich Belyaev,(Дмитрий Константинович Беляев) decided to recreate the evolution of wolves into domestic dogs by launching a unique science experiment.
Belyaev believed that the key factor in the prehistoric evolution of the domestic dog had been its ‘tamability’- or more specifically breeding ‘out’ a wolf’s more aggressive traits and breeding ‘in’ more human oriented traits such as friendliness and responsiveness to contact with humans.
Belyaev believed he could recreate the evolution of the ‘dog-like wolf’ in only a few generations instead of the thousands of years it took for our prehistoric ancestors to achieve the same result. Instead of using wild wolves as his ‘guinea pigs’ he used wild silver foxes- a genetic variation of the wild red fox (Vulpes vulpes) and a close cousin of the wolf.
How was he going to carry out this unusual science investigation?
To start his science experiment he bought 130 foxes from nearby fur farms. On taking possession of the foxes Belyaev placed his foxes in cages and observed their behavior. Following on from his observations and interactions with the foxes he placed each of them them into different categories.
Belyaev’s categories are summarized below:
Class III– Those foxes that run away from humans or bite when handled.
Class II– Foxes that tolerate humans stroking or handling them but are not friendly.
Class I – Foxes which are friendly towards humans, wag their tails and whine for attention.
Belyaev would only bred from the ‘tamer’ foxes and it took him only a few generations to breed foxes that exhibited ‘Class I’ characteristics.
However Belyaev’s breeding programme proved to be so successful that after six generations he added a new ‘superclass’ of tame fox – Class IE. Foxes in Class IE were the ‘domesticated elite’- eager to establish contact with humans, whimpering to attract attention and sniffing and licking humans to establish a closer bond.
More than 50 years after he started his science experiment the results of Belyaev’s experiment can still be seen today. 70% of all foxes now bred at the institute Belyaev founded at Novosibirsk in Siberia belong to the elite class of tame fox!
The evolution of the wild wolf into domesticated ‘dog-like wolves’ originally took place over thousands of years. By a programme of intense selective breeding Belyaev had managed to compress that evolutionary process into a few years!
Not only did the behavior of the silver foxes change, but their appearance also changed.
The skulls of the domesticated foxes became smaller and wider; their snouts became shorter; their ears became floppier; they lost pigmentation in parts of their heads and bodies. Notice that the fox in the image above has a light colored coat and white markings.
It is interesting to note that, following domestication, many animals became ‘piebald’ in color- that is they develop white patches on darker colored fur.
As you carry out your science investigation remember evolutionary biologist Jared Diamond’s maxims. These are briefly stated below- alternatively you can read them in more detail at Livescience.com
Jared Diamond summarizes the traits that wild animals require if they are to be domesticated. These traits include:
*A readiness to eat a flexible diet and consume a wide variety of foods.
*Fast growth and sexual maturity allowing quicker ‘selective artificial breeding’.
*An ability to be bred in captivity.
*A pleasant disposition and little aggression towards humans.
*A temperament that makes organisms unlikely to panic and take flight when nervous. Those organisms that show a ‘flocking’ instinct when nervous can be herded by humans and dogs.
*A willingness to modify their social hierarchy and recognize humans as the pack leaders.
Do dogs ever lose their wolf ancestry?