About a week ago, I asked my friends on Facebook whether there was really any chance that Scotland would leave Britain. At that point, the “yes” vote was running solidly behind, and it seemed likely that this would follow the path of such referendums in Quebec and elsewhere: close, perhaps, but no cigar.

Whatever the downsides of union, Scotland is not South Sudan; I expected that voters would ultimately look at all the complications of departure and decide to stay.

But the most recent polls have surprised me (and apparently, the British government): Some polls show independence pulling into the lead, though others show it well behind. I’d still give the moderate edge to the “stay” camp. But it seems entirely possible that come Sept. 18, the world will see an independent Scotland for the first time in centuries.

My basic position on this sort of thing is that if places want to be independent, they should be independent, unless the reason that they’re seeking independence is so they can have more freedom to oppress minority populations.

Yet I can’t say this seems like a good idea, for reasons that my friend Alex Massie has ably outlined. Scotland is a net recipient of transfers from the British government, so going it alone will probably require some belt tightening. The process of separating all the intertwined institutions, from banking to education, will be daunting.

But the very closeness of the vote shows how hard it can be to focus on bloodless practical considerations in the face of ethnicity and culture. Even in our enlightened age, people really don’t like having their fates controlled by outsiders.

Jonathan Haidt has a good word for it: People are groupish. Our first major advance as a species was forming small, social, cooperative groups. That has many survival advantages, but one of the characteristics of those groups that helps them survive is that they are extremely sensitive to the difference between “Us” and “Them,” more concerned about threats from strangers than intimates – often irrationally so.

The cosmopolitan class finds it easy to forget how deep these sentiments run. Really, it’s not that we don’t understand or, for that matter, endorse groupish behavior; it’s just that we find it a lot easier to do the cost-benefit calculations when our own group isn’t involved.

It’s not really all that surprising that groupish instincts might prove more convincing than fiddling details about how to handle redenomination of Scottish bank accounts if the new nation should find it necessary to develop its own currency.

There’s one easy way to override them, of course: an outside threat from an even bigger, stranger group. Small differences are easily glossed over when there are some really foreign people knocking at the gates. But the rich world is largely peaceful now, which gives people more time to worry about the jerks next door.

I wonder if it’s a coincidence that as the Cold War recedes into distant memory, separatist urges are making more inroads in places such as Scotland and Belgium.

I still assume that Scotland will ultimately choose to stay. But even if it does, it will do so knowing that a near majority of voters wanted to be citizens of Scotland, not a United Kingdom. Nationalism really isn’t dead; it’s just resting.