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The Truck Gene

By PERRI KLASS, M.D. NY TIMES

My younger son, I used to say, had the truck gene.

I still bring this up sometimes when I talk about the importance of reading aloud to small children, because we had assembled, when my son was 2 or 3, one of the world’s largest collections of truck picture books, a failed parental strategy to diversify our reading-aloud assignments. We had to read the favorites (for example, “Bernie Drives a Truck,” a 1992 work by Derek Radford) over and over and over.

Even today, I look at “The Truck Book” (1978, Harry McNaught) with instant recognition — amazingly, it’s still on the current Amazon list of best-selling children’s car and truck books.

We hadn’t particularly tried to develop this child’s interest in trucks, mind you, and we had plenty of books on other subjects, including a massive inheritance from his older brother which skewed toward pirates — but given the choice on any given night, it would be a truck book, and then another truck book, and then, just for variety’s sake, maybe a tractor book or a bulldozer book.

When I mention the truck gene to a group of doctors, a certain number of the mothers and fathers in the room nod knowingly — they’ve been there, and sometimes back.

But even as neuroscience finds new and fascinating ways of looking at the fine points of neural processing and the interconnections of children’s developing brains, that remarkable and somewhat inspirational individual essence remains elusive: Why do you find some particular topic interesting, compelling, memorable, when it leaves me completely unmoved (and, of course, vice versa)?

This is the mystery of personal taste and personal interest, as in, what interests you and what doesn’t, and it is part of what makes us human, and what makes us individual humans. But it’s kind of amazing that it’s present so early, and so powerfully, as children look around the world; that they are capable of being bitten — hard — by some particular bug (and yes, there are kids with the bug gene).

How come you can go into a room full of children, 3 or 4 or 5 years old, and talk to them about dinosaurs, and most of them will be somewhat interested — but one or two will be truly grabbed, truly converted, truly obsessed? They won’t all grow up to be paleontologists, though Stephen Jay Gould wrote in the dedication for “Ever Since Darwin,” his 1977 book of essays on evolution: “For my father, who took me to see the Tyrannosaurus when I was five.”

So sure, some space kids grow up to be astronauts or aerospace engineers, some horse kids grow up to ride, or go to vet school, some bug kids go into entomology. But the point is not that these are necessarily lifelong interests; many have been known to outgrow the pirate stage, and even the horse stage, the bug stage, the dinosaur stage and, thank goodness, the truck stage. The point is that you cannot make a truck kid into a bug kid; they know what’s interesting, though, like the neuroscientists, they may not know why.

And when something interests a small child, all bets are off in terms of memory and vocabulary. The world is full of sweet little voices pronouncing dinosaur names. My own child, and his collection of truck books, enriched my own vocabulary tremendously; I would point at the picture and he would say, for example, “articulated crash rescue vehicle!” (puts out fires at airports, articulated means it has a flexible part in the middle so it can bend as it goes around curves). Lots of syllables there, no helpful little rhymes in the book, and it didn’t matter a bit. Those words were graven on his soul.

Even by age 2 or 3, it’s easy to remember all kinds of stuff, from complex terminology to obscure facts, about the subject that interests you. And that doesn’t go away; when I study for my medical recertification exam, I am still working harder at the topics that interested me less in medical school (how many times have I memorized the kidney?) and still feeling smug about the ones I liked and learned properly the first time around (those fascinating parasitic worms).

Most of us have had occasion to learn as students and as adults, over and over, that you cannot just decide to be interested in something, even if it would do you some personal or professional good. You can bring yourself closer and learn more and try to work up a relationship to the subject, but be it wine or be it nephrology, if it doesn’t grab you, you’re not going to find great pleasure in reading about it, and the details may not stick in your memory.

For the most part, children’s interests and preferences are an occasion for adult appreciation: you may never come to see the magic in trucks, but that just teaches you over and over that your child is a separate person, looking out from a different brain through different eyes.

Of course, some children develop interests that actually veer toward perseveration and obsession, and that children on the autism spectrum may be prone to “highly restricted, fixated interests that are abnormal in intensity or focus.” That is, in fact, one of the possible criteria for an autism spectrum disorder diagnosis in the latest edition of the DSM. (Back when Asperger’s syndrome was recognized, this kind of special interest was thought to be particularly typical of what Dr. Asperger himself called the “little professor syndrome.”)

So we do sometimes worry about a child with a particularly unusual special interest — vacuum cleaners, for example, or string, or about a child whose special interest seems rigid or restrictive, a narrowing down of the child’s world, rather than a special portal into a larger and more fascinating sphere.

But for most typically developing kids, special interests and special subjects are a source of endless bedtime stories, specialized vocabularies, themed birthday parties and Halloween costumes (we put in quite a few pirate years in my house). Above all, when our children develop strong intellectual preferences — and never doubt it, that’s what we’re talking about here — it should bring on that mildly bemused parental headshaking sense that each child is an individual, with a remarkable, fascinating individual brain.

As the mother of a grown child, no longer expressing the truck gene (“Was I really a truck kid?” he emailed me), I want to promise you that you will one day look at these books with smiles and sentiment. And I am willing to bet that no neuroscientific research will actually tease out the individuality of it all, or satisfactorily explain the appeal to those who lack the truck gene, but find that despite our own complete lack of interest, we have managed to memorize “The Truck Book,” not to mention, of course, “Bernie Drives a Truck.”