A FEW centuries before our millennium began, the last remaining sizeable bit of uninhabited land fit to live in received its first humans. It had taken perhaps 200,000 years for the race to spread from East Africa to what is now New Zealand. Not so long; say, 10,000 generations.

The journey might have taken longer, had not the land masses been conveniently arranged so that nearly all of it could be made on foot. Push north out of Africa, and humanity could turn left for Europe or right for Asia. From the extremity of Asia it was not too hard to get to North America, which happily was joined to South America. Even Australia was accessible via the stepping stones of South-East Asia and some short sea voyages, though it was Polynesian islanders who made the long one to New Zealand.

Why? It is tempting to answer: insatiable curiosity. Humanity could hardly wait to get out of its African birthplace, one might argue. What a wonderful lot we are. But simple curiosity is, by itself, a fairly feeble motive for leaving a secure and familiar place.

There is a painting entitled “The Boyhood of Raleigh”, which shows an aged seaman yarning to young boys and pointing towards the horizon. It was painted by John Millais, and for Victorians like him it expressed the call of the great beyond, adventure for its own sake. But Walter Raleigh, who travelled as much as any man of his Elizabethan day, was happy to return to England, even to face execution. Victorian sentiment persists to this day in daft sagas about space exploration, perhaps the least desirable form of travel ever conceived. But the real motives for the spread of humanity have been chiefly fear, the hope of reward, or a bit of both.

And, once moved, most of the species stayed put, groups and individuals alike. The man of 999 would be astounded by his descendants' mobility today. For most of the millennium, armies, traders, pilgrims and nomadic herdsmen moved, and others did not. Its great mass movements—those of the slave trade, the 19th-century migration to America, the flight of 9m Germans from eastern Europe in 1945-46—were very largely involuntary. Except in towns, the individual household was tied by its crops, or its lord's decision; even short-term movement was limited by bad roads and transport.

Not that the distances travelled on business were always short. Around 1300, the shepherds of Montaillou, the French village studied by Emmanuel Le Roy Ladurie, twice a year crossed the Pyrenees with their flocks on the transhumance, the move to winter or summer pasture, just as shepherds in some countries do today. The women sold their eggs in the market town nearly 20 kilometres (12 miles) away. In the 1480s, Thomas Betson, an English wool-merchant in Calais, often sailed across the Channel to buy 130km west of London, or rode nearly 200km to sell in Antwerp. And this was nothing: Lombard merchants, he lamented, instead of coming—far enough, surely—to buy in Calais, would go direct to his suppliers in England. As another critic of this unfair trade put it,

In Cotteswolde also they ryde aboute.

Other traders, in Asia notably, as is true today, travelled far wider than that.

Yet these were the odd men out. It took the industrial revolution to make everyday mobility possible: on better roads, by train and steamship, today by car, bus—the real people-mover of the third world—and airliner. The wealth brought by the revolution made it affordable. So today hundreds of millions commute 10, 20, 50 kilometres daily to work, while among rich countries' citizens hundreds of millions each year travel to take their vacations hundreds or thousands of kilometres from home.

They do it at speed. The Pilgrim Fathers, who sailed from England to America in 1620, took 66 days. That time had been halved by the 1830s, and the “Great Western” steamship in 1838 halved it again to 15 days. By 1939 the fastest liner took less than five. The fastest mail coach in 1800 took four days for the 600km from London to Edinburgh; by 1910 the luxury Orient Express train took 2 1/2 for the 3,100km from Paris to Constantinople. Each one of these speeds would have amazed people a century earlier; to today's air traveller they are all snail-slow.

True, the pace of advance has been uneven: at the start of the 1970s, the fastest journey by train and boat from London to Paris took only six minutes less than in 1913. But the essence is unaltered: the concept of mobility, strange to most of his forefathers, is a familiar, unremarked reality to modern man. In a world of 6 billion people, the airlines linked in IATA sell some 1.5 billion tickets each year; to 1 billion Indians, Indian Railways sells about 4.5 billion tickets.

Yet we are homebodies still. Physical movement is easy, and, for the developed world, relatively cheap. Communications—the 19th-century growth of reliable postal services, then the telegraph, then telephones and now e-mail—have lessened the main disadvantage of short-term movement, the sad inability of bodies to be in two places at once, and have eased the pain of long-term migration. But now as ever the human race (unlike some birds) does not move for the sake of moving. We need a very solid motive. And, usually, money. Many millions of Hindus make pilgrimages within India each year, millions of Muslims make the haj to Mecca; but hundreds of millions of both faiths choose or have to stay at home.

The lure of the west

For much of the millennium, the main such motive was fear, fuelled often by the intolerance of religion. As late as 1947, it was that sort of fear which drove maybe 14m people across the Indo-Pakistani borders. Four centuries before, seven wars between Catholics and Protestant Huguenots, fought with fanatical cruelty on both sides, had racked France. In the end, the defeated Huguenots fled in their thousands, to Protestant countries in Europe or over to North America, to France's economic loss and the gain of the host lands, particularly America.

The great appeal of America for the persecuted was that, though it had its native peoples, there was plenty of room still for newcomers. And it was quite easily accessible. With today's easy land and air travel, we forget that the sea—and, still more so, navigable rivers—was for a few centuries of this millennium an easier (though seldom easy) route to take, for some journeys, than the land. Coal, for instance, long came to London from north-east England by boat; it was even called sea-coal.

And by around 1600 even the Atlantic had lost some of its terrors. Leif Ericsson, after all, around 1000, had crossed it, probably from Norway by way of Greenland. His settlement did not flourish. But by the time the Huguenots came ashore in large numbers, America was being settled on a fairly regular basis. Ships greatly superior to Ericsson's could now ply the Atlantic reasonably sure of getting their passengers across, and in decent shape. The first permanent English settlement, Jamestown, in Virginia, was 13 years old by the time the Pilgrim Fathers reached Massachusetts.

Though Europe's tensions of religion eased, its Jews were still fleeing across the Atlantic in the 19th and 20th centuries. The 19th-century German Pietists went hoping to spread their version of gospel truth. Political dissidents fled what they considered an increasingly reactionary Europe. But the great migrations to the United States and Canada that raised their joint population from 6m in 1800 to 91m in 1910 were driven not by politics or religion, but economics.

The motive was both pull and push: a better life across the sea, but also, often, a worsened one at home—as for the victims of the 1840s potato blight in Ireland (and other places, like the lower Rhine area). Yet few went happily. Families would wait for a year, then another, if they could, hoping the next would be better. Only when it wasn't did they decide, reluctantly, to move.

Where? A British economist, Edward Ravenstein, noted in “The Laws of Migration”, published in 1885, that migrants preferred to move only short distances from their homes. Some Victorians may have seen romance in the wild blue yonder, but most people are not romantics in that sense. If you did not move too far away, why, you might be able to return when things got better; like 1999's Kosovan refugees, who mostly rejected offers to whisk them to distant lands, and rushed home as soon as they dared.

The great movement of millions across the Atlantic was in part a tribal migration. Whole communities in Europe pulled up their roots, to replant them thousands of miles away. But individual families and people moved too. Even Britain, birthplace of the industrial revolution, was shedding its people at the rate of 250,000 a year in the 1850s. Yet Britain was rich and getting richer. Why not stay and get rich too?

One reason for going was official encouragement. The population was multiplying, and the government took seriously the warnings of Thomas Malthus, 60 years before, that population grows faster than the means of subsistence. Moving from crowded Britain to largely empty North America, and at the same time taking British values, was seen as an act of patriotism. Emigrés sang a popular song of the time:

Brave men are we, and be it understood,

we left our country for our country's good.

Europeans, mostly southern ones, went to South America too, though less fast. Population there grew from 23m in 1800 to 63m in 1900, and big shifts—of Italians to Argentina, for instance—went on well into this century.

The great days of mass tribal migrations are over. The European takeover of the Americas was the biggest. The slave trade took 3.3m West Africans to the Caribbean, 3.7m to Brazil; Arab traders took uncounted millions north from Central and East Africa. The import of Indian labour that has left its mark in Sri Lanka, Fiji, Malaysia, South Africa, even Guyana, has stopped. The results have not been happy for the recipients, such as the Amerindians or Australia's aborigines, ravaged by, initially, the arrival of a mere 150,000 British convicts between 1788 and 1867. But the process—less visibly, in these days of mass short-term travel—goes on.

Those who have moved seldom rush to do it again. The Mongol horsemen who captured much of Asia mostly settled, took wives and raised families. Few black Americans have “returned” to Liberia; even Jewish Americans, deeply committed to Israel, seldom make aliya there. But there are always others ready to move somewhere.

Millions of “guest workers” have moved since 1950 to Europe, from Turkey, from the Arab Maghreb, some even from Vietnam. Brown and black citizens of its ex-empire have moved to Britain. Uneven prosperity within Europe has brought gentle flows from the south to the richer north.

And though governments have become selective, no barrier has been found that can keep determined people out. With some money, passage can be speeded by the growing band of experts in getting round border controls, faking passports, finding countries reluctant to turn supposed asylum-seekers away, or plain people-smuggling. For all its controls, the United States takes in some 1m legal settlers a year. But hundreds of thousands more slip in illegally. Its Pacific island of Guam is currently under assault from thousands of Chinese paying $20,000 or so to be shipped there illegally.

Economic disparities that encourage movement are likely to increase. According to the World Bank, average incomes in the richest countries were 11 times those in the poorest in 1870, 39 times in 1960, and 52 times in 1985. Life in many countries is nasty, brutish and liable to be abruptly shortened. The world today has some 14m-18m refugees, a crude word that lumps together those who have fled for their lives and others simply seeking a better one; or, often, both.

And those who stay at home

Within our millennium, humanity's new mobility has made a new world; above all in the Americas and Australasia, but not there alone. And not new just in its peoples. Ships took European smallpox to the Americas, and brought back “Indian corn”—maize—and, by 1600, the Andean potato. Hungry railway-builders emptied the American plains of bison. Australia is over-run by once-British rabbits, New Zealand by ex-Australian opossums, and both countries prosper on ex-European sheep. Countless habits have spread the same way. The world's tea plantations spring mostly from British experiments in north-eastern India in the 1830s; but leaf from China had taught Europe to drink the stuff 250 years before. And the West, of course, has carried its inventions, its alphabet, its languages, its religion, its clothes, its ways of life worldwide.

Yet for all our new ability to move, all the incentives to migrate, most people do little of either. Mexico is the world's major country of emigration; yet in the past 50 years over 90% of Mexicans have stayed put. Only a fraction of the billions in China and India have ever strayed far from their home village or town. Rich people move more; yet not one Briton in two has taken a holiday abroad. John Howard Payne was a minor 19th-century American dramatist, but he wrote a universal truth: “There's no place like home.”