On Saturday afternoon, a scrimmage of rugby players filled the television screen, bellowing and grunting like stags in rut.

Behind them the camera caught the hills that surround Melrose, one of the most bijou and scenic of the Border towns. While the players wrestled and shouted and made a dash for the touchline, a crowd of 10,000 roared them on through hail and rain. This was the annual rugby sevens league, but those watching could have been forgiven for thinking there had been a time-slip, and they were back in the middle ages - or just a Saturday night after last orders - when revved-up borders clans would attack each other, taking pride in the lost teeth and broken limbs that ensued.

I had spent the previous evening in Peebles, listening to a discussion of John Buchan, in this the centenary year of The Thirty-Nine Steps. That novel helped put the borders on the map for those who had never been north of York and although Buchan had spent only a fraction of his childhood here, it obviously made a profound impression. His high regard for the people in these parts stops little short of awe, but as well as his respect for "a stalwart independence sweetened by courtesy", as he wrote in his memoir, he had a shrewd understanding of the more challenging traits of locals: "Heckling in the Borders is carried to a higher pitch of art than anywhere else in Britain. It is pursued for the pure love of the game, and I have known a candidate heckled to a standstill by his own supporters."

As you travel the B roads to Peebles and its sister towns, there is little traffic save for tractors and quod bikes. Driving past fields of lambs and calves, it is almost possible to imagine that nothing much has changed since Buchan's day. And then one is woken abruptly from this reverie. Cardrona, an incongruous satellite of executive homes on the outskirts of Peebles, is spreading fast along the banks of the Tweed, as if a river of bricks has burst its banks. Soon this eruption of suburban villas will dwarf the town. But it's not only in Peebles that builders are in clover. From Selkirk to Hawick, Jedburgh to Galashiels, there are almost more cranes than Scots pines, as bulldozers pulverize pasture and hillsides in anticipation of hordes of house-buying commuters descending when the borders railway reopens in September.

Meanwhile, archaeologists have begun their search for the long-lost 12th-century abbey they believe lies near Selkirk. Should this be unearthed, it will be Britain's earliest abbey, adding to the tourist trail that will also be boosted when the Great Tapestry of Scotland is housed in Tweedbank.

The question that hangs over all this activity is less of aesthetics - though the encroachment of modern developments is concerning - but more of character. For centuries the borders has been set apart from the rest of the country. Once famed for its lawlessness, it retains a distinctive mood, each town different from its neighbours, but the whole creating a region that is as distinctive in terms of personality and outlook as it is in landscape and geography.

One thing is for sure: there is nothing soft about these parts. Bred for survival, the people's habits and customs can be punishing. Among these are the annual common ridings, when each of the towns rides its marches. My husband fondly recalls a band of his Hawick relatives in the back garden after one of these occasions. They were engaged in their favourite party trick: taking turns to see how hard they could hit each other on the forehead with the back of a metal spoon.

With the coming of commuters and tourists in growing numbers, will the likes of Melrose and Selkirk preserve the characteristics that make them unique? The great worry is that as the attitudes of the central belt begin to encroach, or newcomers start to expect things to be done the way they are everywhere else, the essence of the borders will be diluted: shops will open longer, witty straight-talking will give way to diplomacy, health and safety will mollycoddle junior rugby players, and insist that horse riders show a certificate of proficiency before being allowed into the saddle.

It is, of course, possible that all these things will come to pass, but some of us predict that the psychological tungsten on which the borders is built will prove resistant to outside influence. Rather than being diminished, it is far more likely that the ranks of borderers will be swelled in the coming years, as new arrivals are moulded into shape by a process of acclimatisation, integration and renunciation that ought perhaps to be known as the Thirty-Nine Steps.