The answer lies in your family tree.

Back in February, I wrote about how, in my pre-Internet teens, my curiosity about my family history sent me to the genealogy room at the New York Public Library – where, though I failed to find anything about my father’s forebears (his parents had been poor Polish Catholic immigrants), I managed to trace some of my WASP mother’s lines to colonial-era settlers from England, Wales, Scotland, Ireland, and France. Late last year a family member picked up where I’d left off, and, using today’s extraordinary online resources, soon discovered – as I noted in February – that we’re part American Indian. Soon afterwards, she ascertained that we had Italian and Dutch antecedents. Then she had me spit in a vial, and the DNA results – which I got a couple of weeks ago – informed me that I’m also part Baltic, Swedish, and Jewish.

Swedish? Jewish? Okay, I was hooked. As Al Pacino put it in Godfather III, just when I thought I was out, they pulled me back in. Putting aside my most recent online distractions (geography quizzes and Scrabble in Norwegian), I clambered once again up my family tree, and within a few days I’d traced some of my distaff lines back to the early Middle Ages, locating progenitors in Spain, Hungary, and pretty much everywhere in between.

Of course, I was fully aware that once you get to medieval times, you’ve left behind researching your very own family tree, in the sense of cobbling together something that’s unique to you, and are instead poking around in the lives of people from whom untold millions of us are descended. This past weekend, wondering about the numbers on this, I tracked down a 1998 study by Yale statistician Joseph Chang, who concluded that sometime in the late thirteenth century, there lived a European man or woman who – get this – is a direct ancestor of every white person currently alive.

That’s not all. Go back to a thousand years ago, and one-fifth of the Europeans who lived then have no living descendants today (their gene pools having dried up relatively soon), but every single one of the others is an ancestor of everyone of European heritage living today. “All lines of ancestry,” as statistician Adam Rutherford puts it, “coalesce on every individual in the tenth century.” Five years ago, a DNA study reached the same conclusion as Chang’s math.

Rutherford’s own calculations suggest that the chances that a Briton living today is not a direct descendant of Edward III (1312-77) is one in 100 nonillion. “Everyone from this room,” he recently told a British audience, “is directly descended between 21 and 24 generations from Edward III.” Just last week, as it happens, I found one of my own direct lines back to that particular royal. Yep, twenty-four generations.

You might think that the fact that our family trees all ultimately converge would make it a waste of time, after a certain point, to keep plugging away at this stuff. On the contrary, it’s a neat way to enhance and refresh your historical memory. This time around, every time I’ve added another famous name to my family tree, I’ve googled that person and read up on his or her life. I’ve always loved history, but now it feels considerably less distant. To stumble over Geoffrey Chaucer, Eleanor of Aquitaine, and Charlemagne in your direct ancestral lines, as I have in the last few days, has to affect the way you think about these immense figures – and the way you view your own relationship to history in general.

As it happens, one name in particular really hit home for me when I found it in my tree. That would be the name of Charles Martel – the man who, on the tenth of October in the year 732, led the army that saved Europe from the forces of the Umayyad Caliphate at the Battle of Tours.

Yes, I was aware that every Caucasian on earth today is descended from the guy. But sue me. I still found it moving to be able to trace one meandering line back from me through forty-six (count ‘em, forty-six) specific individuals – all of whom, to those persons immediately above and below them on my chart, were not just names on a computer screen but family – and to wind up at the man who repelled the nefarious forces of Islam at the height of its European power. To follow an ancestral line from yourself to someone like him is to experience a compelling sense not only of one’s flesh-and-blood connection to history but of one’s intense and ineradicable filial obligation to it.

Nailing down that Martel nexus underscored for me a vitally important fact: namely, that one weapon that Muslims have in spades, and that we Westerners don’t at all, is history. They remember these things. We don’t – at least not in the fiercely acute way that they do. In this era of social networks and reality TV, an overwhelming number of us folks in the West inhabit an eternal present, preoccupied by the latest tweets, Facebook postings, and celebrity Instagram photos. We live and die by the daily news cycle, allowing ourselves to get worked up into a lather over trivial events that we’ll forget about in a week. Issues that weren’t even on our radar five years ago (transsexuality, anyone?) now steer what we think of as our moral compass. Meanwhile we have little or nothing in the way of historical perspective. Kids graduating from some of the “best” colleges in America don’t know who fought whom in World War II, let alone World War I or the Napoleonic Wars – or, needless to say, the Battle of Tours.

In this regard, we could hardly be more different from those people in the Muslim world (and, increasingly, in our midst) who are more than willing to sacrifice their earthly lives to drag the nations of the West into the House of Islam. To them, the forty-seven generations that separate you, me, and them from the Battle of Tours are absolutely nothing – nothing at all. They have a feeling of intimacy with their forefathers of fifty-odd generations ago that is a good deal more potent and profound than whatever sense of attachment most of us in the West have with our late great-great-grandparents. Their values and principles, if you can call them that, haven’t changed in fourteen centuries.

Indeed, to any Muslim who’s been properly educated in his faith and in his solemn duties thereto, the very earliest days of Islam – only a little over a century, nota bene, before the Battle of Tours – are realer, more vital, and more significant than his own quotidian existence. That’s a momentous psychological force and a not inconsiderable asset for the jihadist cause; it’s a phenomenon that we in the West, however hard we may try, are probably incapable of fully replicating within our own hearts and minds. But my experience of the past couple of weeks has taught me that even a brief climb up your family tree can give you something of an idea of what that closeness with the past must feel like. And this act of forging ties with our shared Western patrimony, it seems to me, can only aid our current struggle to do for our own posterity what Charles Martel did for us all those centuries ago – namely, to ensure that his and our civilization is saved, yet again, from the scourge of Islam.

Image: Charles Martel at the Battle of Tours