Darwin's Island Page 16

  Darwin was a dog-lover. He devotes the first chapter of The Variation of Animals and Plants under Domestication to the history of those creatures. So great was their diversity even in his day that he was uncertain whether dogs had descended (as in fact they do) from a solitary ancestor, the wolf, or from several, with the fox and jackal as additional candidates (although he did dismiss the widespread view that each breed had descended from a separate wild ancestor, now extinct). As he points out in Variation under Domestication, even barbarians attend to the qualities of their pets, to such a degree that the dogs of Tierra del Fuego have gained the instinctive ability to knock limpets off rocks. The breeders were often ruthless: the book tells of Lord Rivers, who, when asked why he always had first-rate greyhounds, answered, ‘I breed many, and hang many.’

  As Darwin noted, the dog is now the most varied of all mammals, both in mind and body. Some breeds were ancient. On a visit to the British Museum Darwin identified images of a Mastiff on Assyrian monuments from the sixth century BC. Others were more recent and had diverged much more from their wild ancestor. Some attributes - such as the shape of the head and the receding jaw of the Bulldog and Pug - might, he suggested, have arisen as sudden ‘monstrosities’ (or mutations, as we would call them), but the majority came from the slow accumulation of favoured forms. The dog was a marvellous model of how flesh can be moulded by human choice.

  DNA shows that all dogs are the descendants of wolves, which will still cross with them when they get the chance (Domestication tells of ‘the manner in which Fochabers, in Scotland, was stocked with a multitude of curs of a most wolfish aspect, from a single hybrid-wolf brought into that district’). The earliest bones found with those of humans are in a German dig some fifteen thousand years old, and the animals probably loitered around camp-fires long before that - which means that they entered the household well before any other creature. Even in their first days they changed, with shorter legs than their vulpine ancestors as a hint that they no longer roamed the countryside.

  Since then, the animals have been subdivided into a wide variety of forms. Four hundred breeds are recognised and a hundred and fifty have official pedigree societies. Such organisations keep a close eye on their pets’ sex lives and their rules often insist that both parents must belong to a rigidly defined type and that any dubious bloodline must be thrown out. Such exclusivity can lead to rapid change.

  Certain breeds such as Mastiffs, Chows and Salukis have been distinct for centuries (even if the Pharaoh Hound, with its pointed ears and short coat that resemble those of the images on Egyptian tombs, is in fact a fake; a modern copy of an extinct breed). Most, however, are less than four hundred years old, and many are even younger. Their vast diversity is witness to what human choice can do to a once-wild animal.

  In 1815, there were no more than about fifteen designated dog breeds in Britain. The first formal dog show was held in 1859, the year of The Origin. By then the numbers of breeds had risen to around fifty. Many of the most popular of today’s hundreds of varieties - terriers, spaniels, retrievers and so on - trace their origin as distinct breeds no further than the past century, which means that they have gained an identity in no more than fifty or so canine generations. The genes show that almost all were founded by fewer males than females, evidence that - in the ancient tradition that quality passes only through fathers - a popular sire was mated with many bitches. Some males still have over a hundred litters, a pattern at variance with the monogamous sex life of the wolf. The breeders hold to their eccentric belief in the power of sperm over egg and by choosing only the very best as fathers much reduce the size of the available population.

  Sometimes, a single mutation can spark off a new variety. The largest dog, the Irish Wolfhound, stands a metre high at the shoulder and tips the scales at well over fifty kilograms. Sixty Chihuahuas would fit into a single Wolfhound - but the difference in size is due to a single gene, which comes in one form in the big animal and another in the small. The Whippet is a racing dog. It too owes some of its identity to a simple genetic change. Now and again a heavily muscled individual - a ‘Bully Whippet’ - appears in a litter. It bears two copies of an altered gene for a muscle protein and is much misshapen. Most such pups are killed at birth. Many other members of the breed carry just a single copy of that gene. They are faster than average and the gene was unwittingly selected for as the animals were bred for speed (and it has now revealed itself in beef cattle and even in a young German, whose mother was a champion sprinter). Perhaps the most repellent of dogs is the Mexican Hairless, or Xoloitzcuintli, first bred for food and also used as a bed-warmer by the Aztecs. As its name suggests, the creature is entirely bald. A mutation in a gene which in humans leads to loss of hair and sweat glands is responsible (and, unusually enough, ancient statues show that the error has been around for three thousand years). Darwin himself identified a family with the condition - and almost worked out the pattern of inheritance, for he noted that it was passed through daughters but expressed only in sons, which is exactly what is expected from its position on the X chromosome. It was, many years later, the first human gene to be precisely located on that structure.

  A few other dogs, Dachshunds included, also owe their identity to simple inherited errors. For most of the named forms, in contrast, divergence involves many genes. As they build up each type gains its unique appearance. Canine diversity is arranged in a way quite distinct from our own. People, wherever they come from, are more notable for similarities than for differences, but a large part of the variability among dogs as a whole emerges from divergence among breeds. The pedigree clubs have, the double helix proves, been real barriers to the movement of DNA. That in turn has led to intense inbreeding within particular lines. The three hundred thousand Golden Retrievers in Britain trace their descent in the past thirty years to no more than seven thousand males. Other kinds have lost nine-tenths of their total variation in just the dozen or so generations since the 1970s. The dogs have paid a high price. Determined - or deranged - insistence on forcing each line towards an arbitrary standard has led to King Charles Spaniels whose brains are too big for their skulls and Pugs whose eyes pop out so far that they are scratched whenever the animal bumps into something. Pugs are so inbred that the ten thousand in Britain share recent ancestry with only around fifty animals.

  In spite of the genetic damage they suffer, dogs have exploited humans very effectively. They do not pay with their lives, or the products of their bodies, for food and shelter. No other creature is so tied to its master and no other domestic animal has been so subdivided. Most farm animals joined the family far later than did the dog, and some walked into the fields on several occasions and in different places.

  A hamburger has a chequered history. As the Domestication book notes, the cow was tamed on two continents, in Africa and in the Middle East. Cattle were precious long before they were farmed. In the caves around Lascaux, in southern France, are images of more than a hundred aurochs, its gigantic ancestor. That impressive beast roamed wild in Europe, North Africa and parts of Asia and lasted until the 1620s. Sumerians had a cow goddess, the ‘Midwife of the Land and Mother of the Gods’. Later came the Semitic deity Ishtar, whose bull-god partner made enough semen to fill the Tigris. Egypt, too, had a bovine obsession. The Pharaoh was called the Mighty Bull, with a tail on his kilt and bull legs on his throne. The Israelites for a time worshipped a golden calf, and suffered divine displeasure for their ways. The cults of the Minotaur, the toreador and the Western show how the animal retains its emotional power - and some golfers, it is said, still use a desiccated bull penis as a lucky putter.

  The bones of domesticated cattle appeared in the Middle East around nine thousand years ago and in Europe around 5500 BC. Cows continued to mate with wild bulls for thousands of years. Ancient DNA shows that the female, mitochondrial, lineages of today’s European cattle are quite distinct from those of their aurochs ancestors, while their Y chromosomes, the indicators of male ancestry,
resemble the male chromosomes of the huge and extinct bovine. The wild bulls must have continued to impose their desires upon the domestic cows, with or without man’s consent.

  Bacon sandwiches tell a different tale. Pigs came into the household on several occasions, in different parts of Europe and the Near East, with some later input from Asia. Fossil DNA reveals a wave of Near Eastern pigs that moved into Europe and was then replaced by a taming of European wild boar.

  Horses, too, have several origins, one of which is close to the home of the apples in Kazakhstan. Traces of mare’s milk (still popular in that country) on five-and-a-half-thousand-year-old pottery fragments suggest that they were tamed by then. The sex bias by the horse-breeders has been extreme. Ninety-five per cent of the three hundred thousand racehorses alive today bear the same Y chromosome as evidence of descent from a single stallion. His name was the Darley Arabian, who was brought to England from Syria in 1704 by the then British Consul, Thomas Darley (two others, the Byerley Turk and the Godolphin Barb, provided almost all the other chromosomes). Europe has no native sheep or goats and the domestic forms had a simple and single origin in the Middle East.

  The chicken, whose rendered flesh is a staple of the junk-food diet, descends from two or more species of Asian jungle fowl - and is now, with a population of almost thirty billion, the commonest bird in the world. It spread from its home in Thailand to fill Europe and the far Pacific and from there to reach South America before Columbus. In spite of their long years on the farm the birds retain a lot of diversity, perhaps because, like cattle, they continued to cross with their wild relatives. Their reproductive lives have altered more than those of any other creature, for some lay ten times as many eggs a year as do jungle fowl, each egg twice as heavy as those of their ancestors.

  All these animals changed their minds as much, or more, as their bodies as they left the wild. Zoo animals submit to man, but are not tame, let alone affectionate, as many keepers know to their cost. Only animals willing to bow to human desires have even a chance of becoming domestic. As Darwin put it, ‘Complete subjugation generally depends on an animal being social in its habits, and on receiving man as the chief of the herd or family.’ A hundred and fifty million Indian Water Buffalo live in harmony with their owners, but that creature’s close cousin the African Water Buffalo has a strict hierarchy within its herds. The African Water Buffalo is among the most dangerous of all mammals. Its pecking order does not give entry to men and the animal has never been broken in. Elephants are semi-domestic at best and kill many people each year, and plenty of breeds of cattle are happy to attack their masters. Sheep, too, show elements of the fragile personality of their ancestors, for they panic if disturbed. An aggressive animal is no help to man or beast and farms need good behaviour. Men bred from the most submissive, which led farm animals to become less alert, less active and less angry than their ancient fellows.

  Their good nature is coded for within the skull. The brains of domestic animals are, without exception, smaller than those of their ancestors - the pig by a third and the horse by a sixth. The hardest job for the first farmers was to persuade the wild to become tame, but once that behavioural Rubicon was crossed the domestics could afford to put aside their need to outwit Nature and pass the job to ourselves. Many now pass their lives in a sort of calm and extended youth in which the trials of life are dealt with by their masters. The price of tolerating human company was a much diminished intellect.

  Nowhere is the importance of behaviour better seen than by the fireside. The wolf is aloof, suspicious and avoids humans as much as possible. Dogs live in a mental universe quite different from that of their ancestors. Given a choice of dog or man, a wolf cub will run to the dog but a puppy to the human. Wolves hunt in packs, while feral dogs live in chaotic and quarrelsome groups that soon split up. The canine mind has been modified in many ways. Men and women follow another person’s gaze. Point at an object, and all eyes will turn towards it. Dogs share that talent and if its owner indicates where a bone is hidden with a glance or with his hand, the animal runs to the right place. Wolves are baffled by the exercise. So attuned are they to their master’s moods that dogs will yawn when their owner does the same.

  Men become fond of their canine companions - and they return the sentiment, for when left with a stranger the dog plays less than when with its master. The bond between man and pet can last for years, and Charles Darwin himself noted how his own favourite responded to him at once after his long absence on the Beagle. Owners often delude themselves that their pet understands everything they say. That is not true but the animals have without doubt gained an insight into the human mind. They became fully domestic as soon as they could tolerate the other members of their household.

  To gain that talent, the dog brain has been modified. Regions associated with aggression shrink and the hypothalamus, the structure that links the nervous system to the world of the hormones, is much altered. As a result, our favourite pets, unlike their wolfish ancestors, breed all year round. The hypothalamus is also a centre of activity for the nerve-transmitter serotonin, a chemical that, when in short supply in humans, is associated with aggression, impulsive behaviour, depression and anxiety. A deficiency of the stuff is also behind the attacks of rage that affect Springer Spaniels. Other fierce breeds also have low levels. High serotonin may hence be a key to the animal’s calm personality. Drugs that influence its levels in humans (Prozac included) do reduce aggression in dogs as a further hint that the chemical was a key to a place around the fire.

  A remarkable experiment in Russia has begun to disentangle the chemistry of calm. In the 1950s, Dmitry Belyaev became interested in the inheritance of social skills in both animals and man (a risky pastime at the time, for genetics was under attack from Stalin). He began to work on silver foxes, a coat-colour mutant of the red fox, which had first been bred in captivity on Prince Edward Island in Canada in the nineteenth century. Their elegant fur was a valuable commodity in icy Russia, but the caged foxes were almost impossible to control as they were so aggressive and fearful. After a few years he moved his experiment to Siberia, where it continues today.

  At first his stock was suspicious and agitated in the presence of a keeper, albeit far less so than the animals first captured in Canada. Each generation, Belyaev chose as parents those best able to withstand the sight of a human without an attack of frenzy. The rules were strict, for just one male in thirty, and one female in ten, was allowed to pass the test and breed. Within a few generations he saw a great change. The creatures became calmer and friendlier. They wagged their tails and learned to bark. Soon they revelled in human company, and for a time were sold as pets to raise funds. Even their appearance shifted, to embrace piebald coats, curly hair, floppy ears and blue eyes. Like dogs, but not like foxes, they have sex all year round - and like dogs they are good at the hidden food test, while the unselected foxes fail. Thirty generations on, almost all the animals are tame.

  The new and tranquil beasts were cubs that never grew up. Selection for lack of fear led over the generations to an increase in the nerve-transmitter serotonin. Among the few other genes that changed were some involved in the synthesis of the red blood protein haemoglobin, which were less active in the tamed animals. That seems odd, but those proteins also help soak up certain chemicals involved in the serotonin response to stress.

  In fact, the real revolution in the life of the silver fox had taken place long before the Siberian experiment began. Their ancestors in Canada, when first captured, had found it almost impossible to cope with humans. On nineteenth-century Prince Edward Island, where the ‘silver’ mutation was discovered, it took years before any fox could be persuaded to reproduce in captivity, let alone to tolerate a keeper. Once that sexual barrier was breached, artificial selection could begin and the rest of the emotional agenda followed. Like dogs, farmed foxes - of both the amiable and the aggressive stock - diverge from their wild ancestors in the activity of a whole series of brain genes, so
me of which alter transmitter levels. However, there are almost no discernible differences in the activity of a sample of brain genes between Belyaev’s newly serene silver foxes and their unselected and agitated relatives in their cages. Friendliness, it appears, demands fewer mental adjustments than does the simple but formidable task of coping with human company. Most farm animals show few signs of amiability towards man, but for them, and their owners, acceptance is quite enough. To cross that barrier rescued them from the wild. The simulacrum of comradeship, as seen in tamed foxes and domestic dogs, came from later changes in other genes.

  The first farmers modified their charges in both body and mind and their modern descendants do the same in a more rational fashion - but the new way of life altered the ancient farmers’ minds and bodies as well. The new domestics, both plant and animal, were agents of selection upon those who had tamed them. The past ten millennia have been an era of exceptional change for humankind, for Homo sapiens has evolved fast since agriculture began.

  Our own genetic equivalent of the silver fox mutation, the blonde, is a creature of the fields. Just one person in fifty, worldwide, has fair hair. Before Columbus confused matters, almost all of them lived within two thousand kilometres of Copenhagen (and their close relatives the redheads abounded in Scotland, Wales and Ireland). The three or four genes responsible have become common in recent times. Farming is to blame.

  Northwest Europe is (or was, before the development of modern varieties) the only place on Earth where grain can be cultivated north of a line that passes, more or less, through Birmingham. Wheat, barley, rye and the rest need warmth to grow. In the Middle East, where those crops began, the sun shines upon both the fields and those who cultivate them. Our own landscape is dreary for many months of the year, and the peasants till their fields in gloom. Even so, the Gulf Stream imports energy from the tropics and heats up the ground at the end of winter, when Europe is short of sunbeams but seeds need warmth. As a result, the crops can flourish. For the five thousand years since they arrived in northern parts, a grain-based economy depended on Neptune’s help.