It’s in the Neolithic, when humans start to farm, that dogs also start to spread beyond Eurasia for the first time. And they track the spread of farming. Dogs appear in sub-Saharan Africa after the beginning of the Neolithic there, 5,600 years ago, and take another 4,000 years to reach South Africa. Dogs appear in archaeological sites in Mexico around 5,000 years ago, coinciding with the first farmers there, but only reach the southernmost tip of South America 4,000 years later. Studies of mitochondrial DNA suggested that all those early American dog lineages were completely replaced, following the European colonisation of the Americas. But the latest genome-wide studies tell a different story: European dogs – arriving with colonisers in just the last 500 years – mixed with the indigenous New World dogs.
The modern breeds that we know so well take much longer to arrive. They are very recent inventions. Dog genes reflect this history. There are signs of two prominent genetic bottlenecks amongst the ancestors of dogs: one at the origin of domestication, and another when modern breeds emerged, in just the last 200 years. Breeders began to focus closely on promoting particular traits, producing dogs that were wonderfully obedient, providing invaluable help with hunting and herding. But the malleability of characteristics under selective breeding became an allure in itself, and so dogs were also bred with specific shapes, sizes, colours and textures. The morphological variety amongst modern dog breeds exceeds that in the whole of the rest of the family Canidae, which includes foxes and jackals as well as wolves and dogs.
There are nearly 400 breeds of dogs today, and most of them – in all their wonderful diversity – have really only been around since the nineteenth century. This is when the strict breeding needed to create and conserve the kinds of strains recognised by kennel clubs really got going. The breeds that appear to be most ancient, with the most deep-rooted lineages on the dog family tree, are actually found in places where dogs only arrived relatively recently. Dogs arrived in the islands of south-east Asia 3,500 years ago and in South Africa around 1,400 years ago and yet these areas are home to a number of ‘genetically ancient’ breeds: basenjis, New Guinea singing dogs and dingoes. This pattern shows that these lineages have been isolated for longer than most other breeds. The deep roots don’t mean that their lineages were the first to branch off, but rather that out on the periphery they have stayed the most genetically distinct.
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Lots of breeds with supposedly ancient roots, however, turn out to be recent recreations. Wolfhounds were, as their name suggests, used to hunt their wild cousins – very successfully. By 1786 there were no wolves left in Ireland, and so no need for wolfhounds. By 1840, the Irish wolfhound had also gone extinct. But then a Scotsman living in Gloucestershire, Captain George Augustus Graham, resurrected the ‘Irish wolfhound’ by breeding what he thought was a wolfhound of some kind with Scottish deerhounds. Today’s population of Irish wolfhounds comes from a very small group of ancestors so that, like many breeds, they are inbred. And while this helps to maintain the characteristics of the breed, it also increases the risk of particular diseases with a strong genetic component. Around 40 per cent of Irish wolfhounds suffer from some form of heart disease, and 20 per cent from epilepsy. They’re not the only pedigree with problems. Many dog breeds plummeted to near-extinction in the twentieth century, during the world wars, and were resurrected by outbreeding with other types of dog. Very strict breeding since then has produced extremely inbred populations, with little genetic diversity within breeds and an increased risk of diseases – ranging from heart disease and epilepsy, to blindness and particular cancers. Specific breeds are predisposed to certain afflictions: Dalmatians have a high risk of deafness; Labradors often suffer from hip problems; cocker spaniels are prone to developing cataracts.
Breeds may be relatively reproductively isolated now, but their genes tell us that there was once plenty of gene flow between breeds or proto-breeds. Breeds from separate countries share characteristics and genes which show that they must have interbred in the past. The Mexican hairless dog and the Chinese crested dog share hairlessness and missing teeth and in both breeds these traits are caused by precisely the same mutation in a single gene. The odds against this gene mutating in exactly the same way in two different dog populations are infinitesimally small. Instead, these shared traits and shared genetic signature speak of common ancestry. Dachshunds, corgis and basset hounds all have very short legs. Together with sixteen other dog breeds, they all have exactly the same genetic signature associated with this form of dwarfism – the insertion of an extra gene. It’s most likely that this insertion happened just once, in early dogs, long before any of the modern short-legged breeds appeared.
Genetic research provides us with this astonishing opportunity to understand the evolutionary history of dogs, from the pleiotropic exuberance of variety produced by selecting tameness, right through to the selection of peculiar features, suited to very particular tasks, in our modern breeds. We can see how certain mutations, and the traits associated with them, popped up amongst early dogs, and were later – much later – promoted and propagated by selective breeding to create the modern breeds we know today. With inbreeding producing problems with increased risk of disease, geneticists are also working to understand the basis of particularly prevalent diseases and it may be possible to reduce that risk by even more careful selective breeding, and judicious outcrosses, underpinned by genotyping.
Some breeds have been outcrossed beyond the bounds of domestic dogs. Such extreme outcrossing was the basis of the Saarloos wolfdog, created in 1935 by breeding together a male German shepherd with a female Eur
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Hybrid wolf-dogs have attacked and killed a number of children in the US, and are banned outright in some states. In others, wolf-dog hybrids are legal, as long as the hybridisation happened at least five generations ago. In the UK, a first- or second-generation wolf-dog hybrid is considered risky enough to be regulated by the Dangerous Wild Animals Act – the same law governing owning a lion or tiger. It seems odd that breeders would exaggerate the wolf content of their puppies – but wildness is part of the cachet of these animals. With buyers seeking ‘high-content’ and ‘wild looks’, and willing to part with £5,000 to feel more like Jon Snow, wolf-dog hybrids are big business. It’s difficult to know just how ‘wolfy’ the product of a cross is, several generations down the line. The first-generation animals will be 50:50 in their genes, but after that, the shuffling of DNA that happens as eggs and sperm are made introduces messiness – second-generation wolf-dogs could have up to 75 per cent wolf genes in their genome, or as little as 25 per cent. There’s also the possibility that some purported ‘wolf-dog hybrids’ are nothing of the sort, and are just cross-breeds of German shepherds, huskies and malamutes – which already look fairly wolf-like – to create animals which appear even more like wolves. The ‘wolfiness’ of a wolf-dog hybrid, a few generations after hybridisation, is impossible to pin down without genotyping. And even with that genetic measure of wolfiness, it’s difficult to know how this would relate to the potential behaviour of an individual animal.
There are also concerns about wolf-dog hybrids on the other side as dog genes make their way into the genomes of wild wolves. Genetic studies have shown that 25 per cent of Eurasian wolf genomes contain dog ancestry. This is problematic from a conservation perspective – could an injection of domestic dog genes into wild, grey wolves cause problems for Canis lupus? Wolf populations have declined in Europe, under pressure from both hunting and the fragmentation of habitats. But hybridisation could also supply beneficial genes and traits. North American wolves got their black coat colour by interbreeding with dogs centuries, if not millennia, ago. Most hybridisation appears to occur through free-ranging male dogs mating with female wolves, but one recent study showed up dog mitochondrial DNA in two Latvian wolf-dog hybrids. Mitochondrial DNA is exclusively inherited from the mother, so the only way that this DNA could have ended up in wolf genomes is by female dogs having mated with male wolves. Once dog genes have entered wolf populations, it’s very difficult to remove them. Some hybrids look a bit like dogs, but many look exactly like wild wolves. So experts have advised that the best way of reducing the impact of hybridisation is to reduce the number of free-ranging dogs. Once they mate with wild wolves, it’s too late.
Hybridisation raises all sorts of questions. There are biological questions about the integrity of species, and about just how much interbreeding occurs across our once sacrosanct species boundaries. If there’s plenty of interbreeding, with fertile offspring, does this mean our species boundaries are too narrow? These are widely debated questions right now. But in fact, taxonomists, the people who make it their business to name and circumscribe species, have never been quite as rigid as textbooks may have led us to believe. Species are simply snapshots of evolutionary lineages – diverging (and sometimes converging). They are defined by being diagnosably different from the nearest cousins on the tree of life. But sometimes they are defined for human convenience – especially when it comes to conferring separate species names on domesticates and their wild ancestors.
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The potential for hybridisation also leads to ethical questions about the ‘contamination’ of wild species with genes from domesticated species. Having created domesticated species, we’re now keen to preserve any surviving, closely related wild ones. But does this invoke an idea of the purity of species that just doesn’t really exist in the real world? That’s a challenging question, and one that will only become more pressing as our own population grows, and the species we’ve become allied with burgeon alongside us. It’s such a conundrum. The species that have become our allies have secured their future, by becoming companionable, useful, even indispensable to us. But together, we represent a threat to whatever wildness remains.
It seems that the safest way for humans and wolves to co-exist on the planet is to avoid each other. Our ancestors once tolerated wild wolves – long enough to domesticate them. Wolves may be naturally much more shy around humans now than they were in the past. Wolves were changed by becoming domesticated dogs, in so many ways, but the wild wolves may have changed as well. Persecution and hunting of wild wolves probably exerted a selection pressure of its own – the most successful wolves are likely to have been the ones that stayed away from humans. Wolves that are more fearful, and that avoid us, may be products of human-mediated selection – as much as dogs are.
The genetics of grey wolves and dogs suggests that the wolf lineage which gave rise to dogs is now extinct. Times were tough around the last glacial maximum, so that’s certainly possible. But there’s another way of looking at the family tree – that particular lineage of wolves is not extinct at all; in fact, it’s the most populous branch of the wolf family tree: dogs. Genetically speaking, dogs are grey wolves. Most researchers simply subsume them within the grey wolf species, Canis lupus – not a separate species, the previously recognised Canis familiaris, but a subspecies: Canis lupus familiaris.
So that terrier, that spaniel, that retriever that you know so well … it’s a wolf at heart. But a much friendlier one – even more tail-wagging, hand-licking, and altogether less dangerous – than its wild cousins.
