Canid evolution: From wolf to dog -...

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Canid evolution: From wolf to dog

The origins of the dog have been hotly debated at leastsince the early nineteenth century, and it is easy tounderstand why: There are now more than 350 differentdog breeds recognized worldwide ranging in appearancefrom tiny Chihuahuas and “teacup” Yorkshire terriers togiant breeds such as the Great Dane and Saint Bernard. Thedomestic dog is in fact far more variable in size, shape, andbehavior than any other living mammal, so much so that theEnglish naturalist Charles Darwin (1809–1882) doubted thatit would ever be possible to determine with certainty thedog’s true ancestry. He, like several later experts, favored theview that the dog was probably the outcome of mixeddescent from two or more wild species, such as wolves andjackals. Several other authorities have attempted to trace theorigins of the domestic dog to some hypothetical wild dog ofAsia that is now extinct, but convincing evidence to supportthis claim is limited. Nowadays, based on a growing body ofanatomical, genetic, and behavioral evidence, most expertsbelieve that the dog originated exclusively from a singlespecies: the gray wolf, Canis lupus.

Early comparative studies of behavior strongly supportthe wolf’s claim to be the sole ancestor of the domestic dog.Back in the 1960s, the American ethologist John Paul Scottprepared a detailed ethogram, or catalog of species-specificbehaviors, consisting of some ninety different behaviorpatterns for the dog, of which all but nineteen were alsoobserved in wolves. The missing behaviors tended to beminor activities that probably do occur in wolves but hadnot, at that time, been recorded. Conversely, all thebehavior patterns recorded from wolves but not from dogsoccurred in specialized hunting contexts that do not ariseunder domestic conditions. In contrast, the displays andvocalizations of jackals are rather distinctive, and quitedifferent from those of either dogs or wolves. It appears alsothat all of the dog breeds that have been adequately studiedhave common ancestry. Scott and John L. Fuller’s importantwork from 1965 on the genetics and social behavior of sixdifferent dog breeds found no example, in any breed, of thetotal absence of any of the typical canid behavior patterns.More recent anatomical and molecular evidence hasconfirmed that wolves, dogs, and dingoes are all moreclosely related to each other than they are to any othermember of the family Canidae.

Time and place of domesticationDomestication is a process rather than an event, so it

is difficult to pinpoint the precise time and location of theearliest wolf domestication. Apparent associations betweenthe fossil remains of wolves and humans have been un-earthed from sites as old as 500,000 years before the present(BP). There is no evidence, however, that these wolves were

A gray wolf (Canis lupus) in the snow. Tom Brakefield/Bruce Coleman, Inc.

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domesticated or even tamed. The oldest known archaeologicalremains of probable domestic wolf-dogs consist of a pair ofskulls excavated from the Upper Paleolithic site of Eliseye-vichi in western Russia close to the Ukrainian border. The sitehas been dated at between 13,000 and 17,000 years BP. Bothskulls resemble those of Siberian huskies in general shape,although they are larger and broader and have considerablyshorter muzzles. A fragment of a dog’s lower jaw has also beenexcavated from the Upper Paleolithic site of Bonn-Oberkasselin Germany dating from around 14,000 years BP. Fromaround 12,000 years BP a whole series of skeletal remains ofapparent domestic wolf-dogs have also been found in humandwelling and grave sites in Israel, Iraq, and other parts of theMiddle East. All of these animals were morphologicallysimilar to wolves, except that they tended to be slightly smallerand sometimes had overcrowded or compacted teeth. Toothcrowding in early domestic dogs is thought to arise from thefact that selection for small teeth tends to lag behind selectionfor the smaller and weaker jaws associated with a domesticdiet. Overall, the archaeological evidence therefore points toan eastern European or western Asian origin for the domesticdog around 15,000 to 17,000 years BP.

Anatomical and molecular evidence generally supports thedate but not the location of dog domestication derived fromarchaeology. For example, an important feature of dogs’ jawsthat distinguishes them from those of other canids is the“turned-back” apex of the coronoid process on the rear of thejawbone. The only wild canid that shares this feature is theChinese wolf (Canis lupus chanco) from eastern rather thanwestern Asia. Similarly, a recent analysis of variation inmitochondrial DNA (mtDNA) from a large sample of dogsfrom all over the world points to a single East Asian origin forthe domestic dog, probably around 15,000 years BP. (An olderstudy that derived a date of domestication of 135,000 years BPbased on mtDNA evidence is now considered highlycontroversial and should probably be discounted in theabsence of further corroboration.) In the light of currentevidence, it therefore appears likely that the domestic dog wasderived from a single population of East Asian wolvesapproximately 15,000 years BP, and that these early domesticwolf-dogs spread very rapidly throughout the rest of Asia andEurope. Domestic dogs were introduced to the New Worldby Asian colonists around 10,000 years BP, and probablyabout 5,000 years BP reached Australia, where their feraldescendants gave rise to the dingo.

From wolf to dog: How and why?There are several competing accounts of the process by

which wild wolves were transformed into domestic dogs, but itshould be emphasized that all of them are little better thanfables. The truth is that the archaeological record providesfew clues as to the motivations and mechanisms underlyingwolf domestication, and this leads inevitably to a great deal ofunsupported speculation.

One of the most popular theories proposes that wolvesbegan associating with humans, in much the same way thatjackals associate with lions, as opportunistic, commensalscavengers. Gradually, as a result of human tolerance, and

recognition of the dog’s potentially useful role as a garbagecollector, watchdog, and occasional item of food, this casualassociation evolved, or so the theory maintains, into a sort ofpermanent symbiosis. Although favored by a number ofauthorities, the scavenging hypothesis does not explain howthese satellite wolves became fully assimilated into humanfamilies and social groups. It suggests a possible mechanismfor bringing about a closer spatial association between wildwolves and humans, but it fails to account for the developmentof the kinds of close social partnerships so typical of historicaland contemporary dog–human interactions. In addition, moststudies of prehistoric demography suggest that humanpopulations were very small and highly dispersed during theUpper Paleolithic (Bocquet-Appel et al. 2005), so they mayhave been insufficient to provide a viable ecological niche for apermanent population of scavenging wolves.

Another theory, now less popular than it used to be, alsoinvolves the gradual evolution of a symbiotic or mutualisticrelationship between wolves and humans but is based onhunting rather than scavenging. Many recent hunter-foragersundoubtedly use dogs for hunting, and it appears that theirhunting success is improved as a result, at least when huntingcertain types of prey. There may also be some significance tothe fact that the domestication of the dog toward the end ofthe Paleolithic more or less coincided with the invention ofthe bow and arrow—the implication being that hunting dogswould have been useful to Paleolithic hunters for trailingwounded game that might otherwise have been lost using thisnew technology. Unfortunately, the earliest concrete evidenceof dogs being used for hunting derives from Neolithic andpost-Neolithic rock art, several thousand years after domesti-cation. Furthermore, as with the scavenging hypothesis, it isstill necessary to explain the means by which this postulatedhunting symbiosis between wild wolves and humans firstevolved into a true cooperative partnership.

Gray wolves (Canis lupus) exhibit mated pair courtship. Tom Brakefield.Bruce Coleman, Inc.

272 Grzimek’s Animal Life Encyclopedia

Canid evolution: From wolf to dog Evolution


The idea that wolves, like sheep, goats, or chickens, wereoriginally domesticated as food items receives relatively littlesupport in the literature. Archaeological evidence of dogeating, in the form of cut marks on bones, for example, hasbeen found at a number of late Paleolithic and Neolithic sitesin Europe, and the practice is still widespread in certain areasof the world, particularly West Africa, Central America,Korea, China, Southeast Asia, and the Philippines. Dogsacrifice and consumption is (or was) also commonly practicedby many American Indian and Inuit groups. Nevertheless, inglobal terms, dog eating remains a minority activity, and inmost cultures it is viewed as either repugnant or, at best, anextreme starvation measure. At present, there is little evidenceto indicate whether or not Paleolithic peoples killed and atewolves or wolf pups on occasion. And even if they did, onewould still need to explain why they would have elected tokeep and breed domestic wolves for consumption severalthousands of years before they domesticated more palatableand economically viable species such as sheep and goats.

Finally, an alternative theory proposes that the critical stepleading to the domestication of wolves (and perhaps otherdomestic species) toward the end of Paleolithic was thepractice of deliberately capturing, adopting, and keepingyoung wild animals as pets. Pet keeping of this kind isextraordinarily widespread among living and recent hunter-gatherer societies, and it seems reasonable to postulate thatPaleolithic hunting and foraging cultures engaged in similarpractices. According to this hypothesis, the domestication ofwolves would not have been possible until tame wolves hadalready become an integral feature of Paleolithic village life—a process that would have depended on the active adoption,hand rearing, and socialization of wolf pups by people. Criticsof this theory point out that adult wolves are large andpotentially dangerous predators that would have posed anunacceptable risk, especially to children living in theseprehistoric communities. Yet, this applies equally to wolf-dogs serving as either scavengers or hunting partners, and mayalso underestimate the socializing effects of handling byhumans during a wolf pup’s critical early weeks of life.Numerous recent accounts of hand-reared wolves have foundthat, although they are somewhat nervous and predatorytoward other animals, these wolves are remarkably nonag-gressive toward people.

Apart from their casual contribution to communityhygiene and vigilance, these early pet wolves would nothave needed to serve any obvious economic role in order tobe valued by their owners. The relationship would have beenbased on companionship rather than service, just as it isbetween modern pets and their owners. Eventually, ofcourse, dogs acquired important economic and practicalfunctions, such as hunting and guarding, but this probablyoccurred sometime after the process of domestication wasalready complete.

Archaeological evidence offers some support for the petkeeping theory of wolf domestication. Some of the oldestskeletal remains of domestic wolf-dogs from central Europe,the Near East, and North America appear to have beendeliberately buried, either in separate graves or with humans.

The Bonn-Oberkassel wolf-dog, for example, was buried inthe double grave of a man and woman, while the remains of apuppy from Ein Mallaha in Israel was buried roughly 12,000years BP with an elderly person whose left hand wasapparently positioned so that it rested on the dog’s flank. AtKoster in Illinois, some of the earliest remains of dogs in theNew World dating from about 8,500 years BP were evidentlyburied intact in individual graves. Some authorities haveinterpreted such finds as evidence of affectionate rather thanpurely utilitarian relationships between Paleolithic people andtheir dogs.

Whichever account of dog domestication one favors, onething seems reasonably certain: The process probablyrequired the existence of relatively sedentary human commu-nities in which pups could be born and reared in a physicallystable location, at least until they were old enough to travelunder their own steam. Unlike many mammals, wolf pups areborn helpless and blind and must remain in a stationary den ornest until they are old enough to follow adult pack members,usually at around ten to twelve weeks of age. Judging from thearchaeological record, sedentary or semisedentary humancommunities did not appear until the closing stages of the lastice age around 15,000 years BP. Prior to this time, mosthuman populations were highly nomadic, moving from placeto place as local food resources became exhausted.

Changes associated with domesticationThe central mystery of dog evolution, and the one that led

to much of the early confusion and speculation about canineorigins, is how humans managed to generate animals asdiverse in size, shape, and function as domestic dogs in thespace of only 15,000 years. The traditional explanation for thisastonishing transformation is that our ancestors favored andselectively bred from individuals displaying unusual orpromising physical or behavioral traits in order to attain someparticular desired goal, such as the capacity to herd or guardsheep, chase gazelles, bark at strangers, and so on. For thisargument to work, however, early dog owners must have hadreasonably clear ideas about the kinds of dogs they wanted andplenty of variation in canine appearance and behavior fromwhich to choose. In reality, there is little evidence that earlydog breeders ever selected for the gradual accumulation ofsome desired characteristic in dogs, and it is difficult toimagine how they could have done so because the necessaryvariation in phenotype did not exist in the wild ancestor. How,by a process of gradual trait-by-trait selection, could ourforebears have produced the jowly face and lop ears of thebloodhound, the tightly curled tail of the spitz breeds, or thepiebald coat colors of many domestic breeds, when thesefeatures are never seen in wolves? The argument simply doesnot make sense.

To some extent, the same is true when the behavior ofdogs and wolves is compared. Consider, for example,hunting behavior. Hunting wolves display highly character-istic and stereotyped predatory sequences involving combi-nations of trailing, stalking and chasing, biting the livingprey, dissecting the carcass, and often carrying or caching thedissected flesh before swallowing it. A wolf deficient in any


Evolution Canid evolution: From wolf to dog


of one these components of the predatory sequence wouldnot survive long in the wild, and so natural selection hasensured that there is little individual variation in wolfhunting behavior. In domestic dogs, however, some of thesecomponents of predatory behavior are clearly retained andemphasized, whereas others have been de-emphasized or lostaltogether. Dogs such as bloodhounds and beagles, forinstance, excel at scent trailing; border collies stalk and chasesheep but are inhibited from biting them; greyhound-typebreeds delight in chasing and catching prey animals butappear to lose interest once this goal is attained; gun dogssuch as Labradors and spaniels enjoy retrieving and carryingthings, while livestock-guarding breeds such as theMaremma, ideally, show no predatory behavior at all. Howwould our ancestors have been able to select for all of thesedifferent behavioral specializations when the ancestral wolfwas apparently so invariant in behavior?

Some authorities have argued that all or most of thesecharacteristics that distinguish dogs from wild canids such aswolves are the inadvertent outcome of early and intenseselection for just a single trait—tameness—and evidence forhow this might have happened comes from a somewhatunexpected source. In the 1960s the Soviet fur industrydeveloped a problem with farmed silver foxes: The animalswere so nervous and intractable that they were becomingunmanageable. A group of Soviet geneticists were thereforedelegated the task of breeding a strain of docile and tractablefoxes, and they proceeded to do so by subjecting foxes totemperament tests and then selectively breeding from thetamest and most docile individuals. To avoid the problem ofinbreeding, these tamer strains were out-crossed to foxesfrom other farms, and, within about fifteen to twentygenerations, some very unusual things started happening.Not only did they succeed in breeding tamer foxes that

Wolves, like dogs, are pack animals. Tom Brakefield/Bruce Coleman, Inc.




behaved toward people much as dogs do, they also began togenerate an extraordinary amount of variability: Some foxesactually began to look more like dogs than foxes; somedeveloped piebald coats; others had drooping ears or curledtails; some developed diestrous reproductive cycles (wolffemales have only a single estrous each year, in contrast todogs that normally have two); and many were as playful andfriendly as puppies.

It seems reasonable to argue that precisely the sameprocess may have been applied unconsciously to the earliestdomestic wolves—that is, intense selection for tamenessaccompanied by the rapid evolution of increasingly doglikeappearance and behavior. Wolves can certainly be tamed andare said to make affectionate pets, but they also tend to behyperreactive, nervous, or uncontrollable in unfamiliarsituations, and prone to displaying full-blown predatoryresponses toward other animals. Merely by driving away orkilling their most intractable pets, and perhaps selectivelyfeeding and caring for the tamest ones, our Paleolithicancestors may have unwittingly performed the same experi-ment as the Soviet geneticists—thereby gradually suppressingthe wild-type traits and creating a new and highly variablepopulation of domestic wolf-dogs.

The processes responsible for the changes associated withselection for tameness are still quite poorly understood, but it islikely that at least some of them result from the retention ofjuvenile or “neotenous” features into adulthood. This ideacertainly fits with a lot of what scientists know about thebehavior of dogs—for example, compared with wolves, dogsare perpetual puppies who never properly grow up—and it alsoprovides an evolutionary route to the emergence of thedifferent working breeds. For example, mammalian infantsand adults are rather like different species in that each isadapted and specialized to quite distinct modes of life.Connecting these two stages is a juvenile or adolescent phaseduring which the animal’s behavior and physiology isreorganized from the infant to the adult pattern. In otherwords, a sort of metamorphosis takes place. This metamorpho-sis is not as extreme as the one that transforms, say, a tadpoleinto a frog, but it still represents a fundamental reorganizationwhen one compares neonatal and adult styles of behavior.According to some experts, early and intense selection fortameness arrested the domestic dog developmentally duringthis metamorphic stage and, as a result, inadvertently generatedanimals exhibiting a range of incomplete or disorganizedpatterns of adult behavior that could be subsequently co-optedfor the performance of particular specialized tasks.

Hunting wolves display highly characteristic and stereotyped predatory sequences involving combinations of trailing, stalking and chasing, biting theliving prey, dissecting the carcass, and often carrying or caching the dissected flesh before swallowing it. Michael S. Quinton/National GeographicStock.




The process is analogous in some ways to deconstructing apiece of equipment such as a bow and arrow. Oncedisassembled, the constituent parts—the bow, the bowstring,the arrowhead, and so on—can each be used for otherspecialized functions, none of which could be performed bythe fully assembled bow and arrow. Likewise, by interruptingthe development of the normal adult hunting sequence inwolves, early domestication could have produced dogsdisplaying a range of incomplete or partial sequences ofhunting behavior that could then be exploited for a variety ofnovel purposes that wolves were incapable of performing.

The social skills of dogsOne of the first things that happens when animals are

domesticated is that they tend to become physically smallerthan their wild ancestors (Hemmer 1990). The dog is noexception, and the decrease in size is particularly noticeable inrelation to cranial dimensions. When matched for body size,the skulls and brains of dogs are about 20 percent smaller thanthose of wolves.

Perhaps in keeping with their smaller brains, dogs appearalso to be less good at independent problem-solving comparedwith wolves. When researchers have attempted to comparewolves and dogs for their performance on various problem-solving and observational-learning tasks, the wolves tend tooutperform the dogs by a significant margin. Differences inmotivation cannot be excluded as a possible explanation forthis difference. Anecdotal evidence suggests, however, thatwolves are simply better at solving these types of problems.The psychologist Harry Frank, who was responsible for muchof the early research in this area, gives a striking exampleinvolving the observational learning abilities of a malamute, amalamute–wolf hybrid, and a purebred wolf. The latch on thedoor connecting the indoor and outdoor runs of Frank’sresearch facility was relatively complex to operate. Themalamute never learned to operate the latch despite observingpeople opening and closing it for six years. The malamute–wolf hybrid learned the task using his muzzle after watchingpeople for only two weeks, and the seven-month-old wolf

learned the task after watching the hybrid only once. Also, thewolf used her paws rather than her muzzle to perform thetrick (Frank and Frank 1985). This difference between dogsand wolves makes sense. Existence under domesticationgreatly reduces the need for independent problem-solvingabilities because domestic animals are not required to fendentirely for themselves. They are to some extent insulatedfrom the more complex problems of daily living by theirhuman caretakers. Wolves need ingenuity and insight in orderto be successful cooperative hunters in an otherwiseunforgiving world. Dogs, at least to some degree, can relyon humans to solve these kinds of problems for them.

It would be a mistake, however, to conclude from this thatdogs are necessarily less intelligent than wolves. Rather itappears that they have a different kind of intelligence. Dogs,for example, are highly trainable and wolves, typically, are not.Frank spent six months attempting to train his seven-month-old wolf to sit in response to a verbal command, a task thatmost dogs can perform after only a few trials. She neverlearned the trick. Yet this was the same wolf that exhibitedone-trial observational learning when it came to opening acomplicated door latch (Frank and Frank 1985). So wolves areskilled observational learners and relatively insightful when itcomes to solving complex problems, yet they find it extremelydifficult, if not impossible, to do what most dogs manage to dowith relative ease.

More recently, groups of researchers in the United States,Germany, and Hungary have explored these differencesbetween dogs and wolves in more detail and have discoveredthat domestic dogs, even from an early age, are far moresensitive to human verbal and nonverbal signals than hand-reared wolves are, and are far better at using these cues to helpthem solve problems. Using directed patterns of gaze anddistinctive vocalizations, dogs also excel at recruiting humanassistance to solve problems that they cannot solve themselves.The results of these studies suggest that during the process ofdomestication, dogs were selected for a unique set of social-cognitive skills that enabled them to communicate andcooperate with humans to an unprecedented degree (Hareet al. 2002). The problem-solving capacities of wolves arelimited to situations in which there is an obvious functionalconnection between an event or an action and its outcome,presumably because this type of intelligence serves them wellas wild predators. Dogs, in contrast, tend to take their cuesfrom humans and are able to learn behavioral responses thathave no obvious functional connection with their outcomes,such as sitting down in response to a verbal command inreturn for a pat on the head or a morsel of food. This kind ofintelligence would serve little purpose in the life of a wildwolf, but in the context of a domestic existence in partnershipwith humans it has clear survival advantages.

Humans have been exploiting and enhancing these uniquecanine attributes throughout history. The best working dogsnowadays are prepared to work exceptionally hard in returnfor nothing more than human social acceptance and praise.Such dogs are characteristically eager to please, and theyexhibit a tremendously strong social orientation towardpeople compared with hand-reared wolves. Significantly, a

Two young gray wolves (Canis lupus) showing two color phases in samelitter. Tom McHugh/Photo Researchers, Inc.




2005 study found that the descendants of the Russian silverfoxes that were originally selected for tameness display asimilar degree of sensitivity to human social cues (Hare et al.2005). This strongly reinforces the idea that human socialorientation and trainability in dogs were unforeseen con-sequences of early selection for a docile temperament.

ConclusionsThe best available evidence suggests that dogs were

domesticated from wolves in East Asia approximately 15,000years BP. Although the process by which wolves became dogs

has been the subject of considerable speculation, the true storyof how or why this extraordinary relationship first developedwill probably never be known. The process of domesticationtransformed the wolf in a variety of ways. It altered theanimal’s appearance to a remarkable extent and had a dramaticimpact on its mental characteristics. Above all, it createdvariation in morphology and behavior that was not present inthe ancestral wolf—variation that later provided the rawmaterial for the development of all the subsequent specializedworking dog breeds.

It is likely that many of these changes in morphology andbehavior were initiated by early selection for “tameness.” Byselecting for increasingly tame individuals, our ancestorsinadvertently produced a strain of domestic wolves in whicha variety of juvenile or neotenous traits were retained intoadulthood. Coordinated patterns of “instinctive” behaviorcharacteristic of adult wolves became fragmented by thisprocess, and humans later exploited these “fragments” togenerate highly specialized working breeds. A reduced needfor independent problem-solving skills and a greatlyenhanced ability to detect and respond to social cuesprovided by humans also emerged as a result of thedomestication process. Trainability—the capacity to learnnovel behavioral responses to arbitrary human cues—mayhave been another accidental outcome of early selection forpuppylike characteristics. The animal that emerged from theother side of this process of early selection for tameness wasthe true ancestor of all modern dog breeds. It neither lookedlike a wolf nor, strictly speaking, did it behave like one.Instead, it was a new and uniquely variable, “all-purpose”creature whose future working talents were still to berealized and exploited by humans.

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