On every continent, save Antarctica, early humans have left their mark on rock faces. Whether Australia or southern Africa or Asia, there is rock art left behind. The most famous and most familiar, of course, are the cave paintings of Europe. Dating from 30,000 years ago to roughly 10,000 years ago, they are the starting point from which we begin every survey course in art history.

The most famous caves are Altamira in Spain and Lascaux in France, but there are hundreds of others, including the recently famous Chauvet cave in southern France.

I have taught some of those survey courses, but I had never seen any of the actual caves: I had only seen reproductions in my Janson or Gombrich. Several visits now to Europe have given my wife and me the chance to see some of the cultural monuments we had only dreamed of seeing: Chartres, Giverny, the Louvre — and the cave paintings.

You come to think of yourself as an adult, and that you have seen pretty much everything — in general if not in particular — and you develop a skin of insouciance. It is children whose eyes widen, not adults. We measure and compare, we add some small dram of new experience to the old and hold all in emotional proportion.

That ceases to be possible when staring at the bison, aurochs and horses scratched, drawn and painted in the inner recesses of inaccessible caverns, with a palpable lacuna of 20,000 to 30,000 years in between ourselves and the clearly living and breathing — and thinking and feeling — people who left this evidence on the limestone walls.

And we fall in awe that those people we depict as “primitive” cave dwellers could be so artistically advanced, so visually sophisticated. Yet, there is also a kind of glass wall between us and them. We have no idea why they painted and scratched these images; we have no idea what the images meant to them. We are left to guess.

Those guesses fall into two large categories: On one hand, a group of modern people assume the prehistoric people were decidedly primitive, unlike us in so many ways beyond merely not having smart phones; on the other hand, there are those who make the empathetic leap and recognize that the Cro-Magnon human is exactly the same species as we are, with exactly the same brain power, same potential for neuroses, same skills, and that if we had been in their position, we would perform exactly as they did, and so perhaps the cave paintings are not something alien and other, perhaps they can be understood, not as Alley Oop, the cave man, but as mon frere, ma soeur.

The first art we saw is 17,000 years old, on a cave wall in the Vezere river valley of the Perigord region of France. There were bison, reindeer and horses, drawn with an anatomical awareness that European artists didn’t seem to recapture until the Renaissance.

We had planned first to go to Lascaux in Montignac, but the roads are not always well marked in France and we wound up instead in Les Eyzies at the other end of the Vezere valley.

And it all came to us by accident.

The plan was to drive from Angouleme to Montignac to see the Lascaux II reproductions of the cave art of the original, now closed Lascaux caves.

The road wound through green valleys, up over wooded hillsides and over streams. Eventually, we got to Les Eyzies without ever seeing Montignac.

Turns out, that was a good thing.

Les Eyzies is a small village, made up mostly of cafes and souvenir shops, all along a single street below a tall yellow limestone cliff. These bluffs line the river valley. In them are dozens of caves, and many of those have prehistoric art in them.

Lascaux, further north just outside Montignac, is, of course, much more famous. But the cave has been closed for decades; a substitute cave, called Lascaux II is open to tourists, featuring recreations of the original art. It had been our intention to visit that cave first, and then perhaps check out some of the other, lesser sites along the river valley.

But because we came the wrong way, we found the Grotte de Font-de-Gaume, which is one of the only remaining caves with polychrome painting still open to the public. They protect the cave as well as they can by only allowing 12 people in at a time, and fewer than 200 a day. You have to make an appointment.

So, we stopped by the office — a shack with books and souvenirs for sale — and asked if it might be possible to get a ticket for the next day.

“We are closed Saturday,” she said. “But we have tickets available for this afternoon at 3.”

It was about 12:30 at the time. So we bought our tickets and drove around the countryside, looking at the paysage and enjoying the many roadside attractions, like the Prehisto-Parc, which features those familiar papier mache Neanderthals bagging a concrete mammoth. We passed on going in.

We drove all the way to Montignac, just to see the scenery, and, boy were we even happier we had come the wrong way.

Many years ago, when Carole and I first visited Canyon de Chelly on the Navajo reservation, we came to it the back way, along a dirt road from New Mexico. We didn’t know what we were looking for and got lost on the back roads through the forest. But eventually, the road started down the side of a cliff and we saw a large hole in the ground a couple of miles ahead. It was Canyon de Chelly, and the road led us up to it with no traffic, tourists or souvenir shops. We came upon it — actually upon Wild Cherry Canyon, a side canyon — and got out of the car and had the canyon to ourselves, looking 400 feet straight down into a rock hole. It was awesome. It was only later, getting to the head of the canyon, that we saw the traditional entryway, Chinle, a godawful tourist hole rank with traffic and jewelry stands. If we had come to Canyon de Chelly through the front entrance, we would have been put off by the wretched poverty of the Indians and the rancid commercialism of the dusty town.

So it was at Montignac, a fussy, busy, crummy town, catering to the worst of the tourist trade. If we had seen it first, we would have held our noses, visited Lascaux II and gotten the hell out of Dodge as fast as possible.

But coming up through Les Eyzies instead, we got a boat load of prehistoric places, smaller and less commercialized than Lascaux II, and we found a hotel a few miles north of town called the Hotel Peche-Lune, a large, new hotel with large, clean rooms and a great restaurant out front.

By then, we had used up our extra time and came back to Font-de-Gaume, in time to begin our tour.

It was an unannounced trek uphill for 500 meters, a grueling bit of alpine climbing for Carole and me, huffing and puffing, 20 yards behind the rest of the group, and losing ground.

At the top, there was a hole in the mountain and our guide took us 12 in to see the cave paintings. The cave is not the wide, high sort of Carlsbad Caverns sort of cave, but a seam in the limestone eroded out, about 120 meters into the hill, with several side cavities off at a good Karstian 90 degree angle. At its narrowest, the cave rubbed both shoulders, and there were a few places I had to duck my head, but mostly, it was wide enough for one or two people to pass, and in the main grotto, the ceiling was 100 feet up.

It is dark inside, with a faintly lighted footpath, and a few round lights on the wall that were switched on to dimly illuminate a three-foot bison on the wall about a foot above head height. No, there was another one a little on. And another. Actually there were five bison in the first section of the cave. The first was the clearest, hunch-shouldered, battering ram head, tiny legs and a wooly coat of brown. A small hole in the rock served as the beast’s eye.

The first impression is that the paintings are so faint as hardly to be visible at all. But as you get used to the low illumination in the cave, you realize that what is actually surprising is that they are still visible at all after 17,000 years. It is an astonishing passage of time: 15,000 years before Christ. 12,000 years before the Great Pyramid at Giza. That we could see them at all has to be a miracle.

We moved down the corridor of the cave to another spot, where we saw a giant reindeer, maybe 4 feet long, with a great hoop of antlers curved in a giant C from his head and forward. The shoulders and antlers were the clearest to see, the head, partly painted and partly incised in the stone, was more difficult to make out, but when you did, you saw the reindeer was licking another animal standing in front of it: another reindeer, facing the opposite way, darker and more obscure.

There were more bison and some horses, and what struck you, after realizing how faint some of the imagery was, was how beautifully they were drawn. It is the drawing, not the painting, that is the most notable.

The painting is really bichrome: There is black, mostly for outline, and there is a kind of white, faintly yellow, and there is the ocher mixture of the two, making the brown.

Why are these images here? Who made them? You cannot help but agonize over their meaning. Over the years, there have been many proposed explanations, but none of them really help.

Surely, you think, the paintings might have been the only part of some more elaborate installation that has otherwise long rotted away. We’ll never know.

Over dinner, Carole and I came up with a dozen stories.

I mentioned the football “Game Plan Theory,” with Xs and Os on the blackboard to teach the tactics of the game. Perhaps some ancient hunting teacher was showing the younger generation the ropes.

Or perhaps it was a school, says Carole. One bison, two bison, three bison, learning to count.

She also wondered if they might not have been painted not by adults, but by children, or a single child especially talented at art. And perhaps they are in the caves because that child kept them as his secret place, where he decorated his play fort walls with his drawings.

I said that we should not rule out the possibility that they were created not by men or boys, but by women. “It has to be possible,” I said. “Perhaps the cave was the place in which women were isolated for their menses. Many primitive societies do such things.”

“Then I would expect the animal paintings to be about mothers and calves, or animals giving birth,” she said.

The usual explanations about magic and shamans might be true, but I wondered if we don’t too often condescend to our ancient forebears.

“These were Cro-Magnons, which means they were modern humans in every anatomical aspect. They were exactly the same species as us, with exactly the same brainpower. The only difference between then and now is cultural: We have built on the culture we inherited, as our grandfathers built on the culture they inherited, from the pickax to the digital watch.

“Perhaps we should ask what would we have made these paintings for. Maybe the answer isn’t some tribal woo-woo, heebie-jeebies, but something as practical or as quotidian as our own lives.”

I wasn’t sure what that would be: Certainly these cave paintings were not made as art galleries. Seeing them is a pain in the ass, and there is no track lighting, to say nothing of the lack of white wine and cheese.

It used to be thought that the paintings were hunting magic, capturing the image of the animal to be hunted, to make it easier to capture the meat on the hoof. But recent studies of the caves make it clear that the animals in the paintings were not prey animals. The cavemen did not eat bison or lions or bears.

The second theory is that they were “animal masters,” that is, the animals of cult worship, and the painting of them was a magical means to capture their power, their emotional power.

My own best guess is that they might have been images for meditation, something to concentrate on to bring the observer into an altered state of consciousness. Certainly, many of the drawings — at least elsewhere in the world — contain odd hallucinogenic dots, crosses and spiral patterns, the same imagery that modern drug-religion ceremonies induce and that can be seen in Huichol paintings.

The thing is, we’ll never really know. Almost certainly, vital evidence has disappeared over time, rotted into oblivion: The paintings are denuded of their context and we have nothing to go on but the measly remains, not even so much evidence as dinosaur bones.

We discussed this all over a great dinner at our hotel: We began with a salade de perigourdaise, which was lettuce, foie gras on toast, and lots of duck innards skizzied up and hot. It was surprisingly delicious and very meaty. Carole picked at the lettuce, but couldn’t bring herself to eat duck parts she couldn’t recognize: gizzards, livers — for all we knew duck tongues and spleens.

The main courses were better accepted by a wider population of the Nilsen household. Carole had a faux filet — a beefsteak — bien cuit, thank you very much, and some sliced, fried potatoes. I had a magret de canard with the same potatoes. My duck was really great.

“Duck, the OTHER red meat,” I said.

I saw no ducks on the cave walls. Surely they enjoyed ducks as much as I do.