"You can swallow the most fatal poisons indefinitely if they are in a few parts per trillion," Seeker said slowly.

             As she grew to know this beast it had come to seem more approachable, less strange. Yet a cool intelligence lurked behind its eyes and she never quite knew how to take what it said. This ready use of numbers, for instance, was a sudden veer from its usual eloquent brevity.

             "The robots must know that."

             "True, but consider ozone. A poisonous gas, blue, very explosive—and a thin skin of it over the air determines everything."

             Cley nodded. Through the long afternoon of Earth the ozone layer had been leached away countless times. Humanity's excesses had depleted the ozone again and again. Oscillations in the sun's luminosity had wrenched the entire atmospheric balance. Once a great meteor had penetrated humanity's shields when they had fallen into neglect, and very nearly destroyed civilization. All this lay buried in ancient record.

             Seeker yawned. "The robots worried over managing such delicate matters. So they simplified their problem."

             "They seem in control here."

             "They fear what they cannot master."

             "But they did master much—Alvin made them revive the biosphere."

             "And bring the chaos of biologic."

             Seeker lay back with a strange thin grin and scratched its ample blue belly. Wreaths of jade mist curled ripely over the heat bush. Small animals had ventured into a circle around the black shrub as its steady warmth crept through the air. Few animals feared either Cley or Seeker; all species had for so long been clients and partners. They even seemed to understand Seeker's lazy talk. Cley suspected they were hypnotized by the luxuriant singing tones of Seeker's voice, ready yet eloquent. The circle had relaxed as though the bush was a campfire. A true fire, of course, would have risked detection by the Supras.

             Cley listened as Seeker described the world view of its kind. Long after the Ur-humans, some beasts had risen to intelligence and had engraved in their own genes elements of racial memory. To instill in wise species a concern for their fragile world it had been the custom for many millions of years to "hard-wire" a respect for evolution and one's place in it. This had become a social cement as deeply necessary as religion had been to the earliest human forms, and even in the Ur-humans.

             "Many organisms lorded over the Earth," Seeker said, "beginning with gray slimes, moving on to pasty blind worms, and then to giant oblivious reptiles—and all three persisted longer than you Ur-humans." Seeker snorted so loudly it alarmed her. "We do not know if the dinosaurs had religion."

             "And your kind?"

             "I worship what exists."

             "Look, our tribe chose not to try to learn all that dead history— we had a job to do."

             "And a good one."

             "Right," she said with flustered pride. "Tuning the forests so they'd make it in spite of all this junk in the air, the plants slugging it out with each other—this isn't a biosphere yet, it's a riot!"

             "But a fruitful one." Eyes twinkling, it fished a piece of fruit from some hidden pouch of its fleshy fur. Seeker grinned, a ferocious sight. The moods of the beast were easier for her to read now and she shared its quirky mirth.

             And she saw Seeker's argument. The robots had helped humanity accent its intelligence and ensure the immortality of all in Diaspar. But to make the world work the robots had to run a skimpy, dry biosphere whose sole pinnacle was a palsied, stultified Man.

             A fat, ratlike thing with six legs ventured nearer the bush. Instantly a black cord whipped through the damp air and wrapped around the squealing prey. A surge dragged the big rodent into a maw that suddenly opened near the bush's roots. After it closed on its supper Cley could hear the strangled cries for several moments. Evolution was still at work, pruning failures from the gene pool with unblinking patience.

26

             Next morning the fog began to clear. Seeker kept studying the sky. They had made steady progress climbing the flanks of the saw-toothed mountain range, and now the terrain and rich fauna resembled the territory where Cley had grown up. She searched the distant ridgelines for hints of lookouts. Hers was not the only tribe of Ur-humans, and someone else might have escaped, despite Alvin's certainty. She asked Seeker to tune its nose to human tangs, but no traces stirred the fitful breezes.

             Twice they sought cover when flying foxes glided over. By this time surely the Supras would have sent their birds to reconnoiter, but neither her nor Seeker's even sharper vision could make out any of the ponderous, wide-winged silhouettes.

             They were watching a vast covey of the diaphanous silvery foxes bank and swoop down the valley currents when Seeker motioned to her. Distant rumblings came, as though the mountains above them rubbed against a coarse sky. The foxes reacted, drawing in their formation like silver leaves assembling a tree.

             Blue striations frenzied the air. The few remaining clouds dissipated in a cyclonic churn.

             Cley said, "What—"

             Sheets of yellow light shot overhead. A wall of sound followed, knocking Cley against Seeker. She found herself facedown among leaves without any memory of getting there.

             All around them the forest was crushed, as though something had trampled it in haste. Deep booms faded slowly.

             An eerie silence settled. Cley got up and inspected the wrenched trees, gagging at fumes from a split stinkbush. Two flying foxes lay side by side, as though mated in death. Their glassy eyes still were open and jerked erratically in their narrow, bony heads.

             "Their brains still struggle," Seeker said. "But in vain."

             "What was that?"

             "Like the assault before on your people?"

             "Yes . . . but this time"—she swept her hand to the horizon of mangled forest—"it smashed everything!"

             "These foxes took the brunt of it for us."

             "Yes, poor things . . ." Her voice trailed off as the animals' bright eyes slowed, dimmed, then closed.

             "It does not know precisely where we are, so it sends generous slabs of electrical energy to do their work."

             Seeker gently folded the two foxes into its palm and made a slow, grave gesture, as if offering them to the sky. When Seeker lowered its claws Cley could not see the foxes and they were not on the ground or anywhere nearby.

             "What—"

             Seeker said crisply, "I judge we should shelter for a while."

             They climbed swiftly up the rough rise to a large stand of the tallest trees Cley had ever seen. Long, fingerlike branches reached far up into the air, hooking over at the very end. She felt exposed by moving to higher ground, closer to the sky that spat death. From here she could see distant banks of purple clouds that roiled with spokes of virulent light. Filaments of orange arced down along long curves.

             "Following the magnetic field of Earth," Seeker said when she pointed them out. "Probing."