The physical samples, though, were by far the most valuable items. Once they brought them back, they could be studied at great length using far more sophisticated equipment — the new equipment the xenos on the new colony ship would bring.

At night, Sel lay awake for long hours, thinking of what he and Po had seen, classifying it in his mind, trying to make sense of the biology of this world.

But when he woke up, he could not remember having had any great insights the night before, and certainly had none by morning light. No great breakthroughs; just a continuation of the work he had already done.

I should have gone north, into the jungles.

But jungles are far more dangerous to explore. I'm an old man. Jungles could kill me. This temperate plateau, colder than the colony because it's a little closer to the poles and higher in elevation, is also safer — at least in summer — for an old man who needs open country to hike through and nothing unusually dangerous to snag or snap at him.

On the fifth day, they crossed a path.

There was no mistaking it. It was not a road, certainly not, but that was no surprise, the formics had built few roads. What they made were paths, and those inadvertent, the natural result of thousands of feet treading the same route.

Those feet had trodden here, though it was forty years before. Trodden so long and often that after all these years, and overgrown as it was, the naked eye could trace the path of it through the pebbly soil of a narrow alluvial valley.

There was no question now of pursuing any more flora and fauna. The formics had found something of value here, and archaeology took precedence, at least for a few hours, over xenobiology.

The path wound upward into the hills, but not terribly far before it led to a number of cave entrances.

"These aren't caves," said Po.

"Oh?"

"They're tunnels. These are too new, and the land hasn't shaped itself around them the way that it does with real caves. These were dug as doorways. All the same height, do you see?"

"That damnably inconvenient height that makes it such a pain for humans to go inside."

"It's not our purpose here, sir," said Po. "We've found the spot. Let's call for others to explore the tunnels. We're here for the living, not the dead."

"I have to know what they were doing here. Certainly not farming — there's no trace of their crops gone wild here. No orchards. No middens, either — this wasn't a great settlement. And yet there was so much traffic, along that single path."

"Mining?" asked Po.

"Can you think of any other purpose? There's something in those tunnels that the formics thought was worth the trouble of digging out. In large quantities. For a long time."

"Not such large quantities," said Po.

"No?" said Sel.

"It's like steel-making back on Earth. Even though the purpose was smelting iron to make steel, and they mined coal only to fire their smelters and foundries, they didn't carry the coal to the iron, they carried the iron to the coal — because it took far more coal than iron to make steel."

"You must have gotten very good marks in geography."

"My parents and I were born here, but I'm human. Earth is still my home."

"So you're saying that whatever they took out of these tunnels, it wasn't in such large quantities that it was worth building a city here."

"They put their cities where the food was, or the fuel. Whatever they got here, they took little enough of it that it was more economical to carry it to their cities, instead of building a city here to process it."

"You may grow up to amount to something, Po."

"I'm already grown up, sir," said Po. "And I already amount to something. Just not enough to get any girl to marry me."

"And knowing the principles of Earth's economic history will attract a mate?"

"As surely as that bunny-toad's antlers, sir."

"Horns," said Sel.

"So we're going in?"

Sel mounted one of the little oil lamps into the flared top of his walking stick.

"And here I thought that opening at the top of your stick was decoration," said Po.

"It was decorative," said Sel. "It was also the way the tree grew out of the ground."

Sel rolled up his blankets and put half the remaining food into his pack, along with their testing equipment.

"Are you planning to spend the night down there?"

"What if we find something wonderful, and then have to climb back out of the tunnels before we get a chance to explore?"

Dutifully, Po packed up. "I don't think we'll need the tent in there."

"I doubt there'll be much rain," Sel agreed.

"Then again, caves can be drippy."

"We'll pick a dry spot."

"What can live in there? It's not a natural cave. I don't think we'll find fish."

"There are birds and other creatures that like the dark. Or that find it safer and warmer indoors. And maybe a species of some chordate or insect or worm or fungus we haven't seen yet."

At the entrance, Po sighed. "If only the tunnels were higher."

"It's not my fault you grew so tall." Sel lit the lamp, fueled by the oils of a fruit Sel had found in the wild. He called it «olive» after the oily fruit on Earth, though in no other attribute were they alike. Certainly not flavor or nutrition.

The colonists grew it in orchards now, and pressed and filtered it in three harvests a year. Except for the oil the fruit was good for nothing except fertilizer. It was good to have clean-burning fuel for light, instead of wiring every building with electricity, especially in the outlying settlements. It was one of Sel's favorite discoveries — particularly since there was no sign the formics had ever discovered its usefulness. Of course, the formics were at home in the dark. Sel could imagine them scuttling along in these tunnels, content with smell and hearing to guide them.

Humans had evolved from creatures that took refuge in trees, not caves, thought Sel, and though humans had used caves many times in the past, they were always suspicious of them. Deep dark places were at once attractive and terrifying. There was no chance the formics would have allowed any large predators to remain at large on this planet, particularly in caves, since the formics themselves were tunnel makers and cave dwellers.

If only the formic home world had not been obliterated in the war. What we could have learned, tracing an alien evolution that led to intelligence!

Then again, if Ender Wiggin had not blown the whole thing up, we would have lost the war. Then we wouldn't have even this world to study. Evolution here did not lead to intelligence — or if it did, the formics already wiped it out, along with any traces the original sentient natives might have left behind.

Sel bent over and squat-walked into the tunnel. But it was hard to keep going that way — his back was too old. He couldn't even lean on his stick, because it was too tall for the space, and he had to drag it along, keeping it as close to vertical as possible so the oil didn't spill out of the canister at the top.

After a while he simply could not continue in that position. Sel sat down and so did Po.

"This is not working," said Sel.

"My back hurts," said Po.

"A little dynamite would be useful."

"As if you'd ever use it," said Po.

"I didn't say it would be morally defensible," said Sel. "Just convenient." Sel handed his stick, with the lamp atop it, to Po. "You're young. You'll recover from this. I've got to try a new position."

Sel tried to crawl but instantly gave up on that — it hurt his knees too much to rest them directly on the rocky floor. He finally settled for sitting, leaning his arms forward, putting weight on them, and then scrabbling his legs and hips after him. It was slow going.

Po also tried crawling and soon gave up on it. But because he was holding the stick with the light, he was forced to return to walking bent over, knees in a squat.