Thick hindquarters, propelling them in brisk steps. Short fore­ limbs, ending in sharp claws. Their large heads seemed to be mostly teeth, sharp and white above slitted, wary eyes. A thick brown pelt covered them, growing bushy in the heavy tail they used for balance.

 Days before, from the safety of a high tree, Ipan had watched some rip and devour the soft tissues of a gigantelope out on the grasslands. These came sniffing, working downslope in a skirmish line, five of them. Sheelah and Ipan trembled at the sight. They were downwind of the raboons and so beat a retreat in silence.

 There were no tall trees here, just brush and saplings. Hari and Sheelah angled away downhill and got some distance, and then saw a clearing ahead. Ipan picked up the faint tang of other pans, wafting from across the clearing.

 He waved to her: Go. At the same moment a chorus rose behind them. The raboons had caught the scent.

 Their wheezing grunts came echoing through the thick bushes. Downslope there was even less cover, but bigger trees lay beyond. They could climb those.

 Ipan and Sheelah hurried across the broad tan clearing on all fours, but they were not quick. Snarling raboons burst into the grass behind them. Hari scampered into the trees—and directly into the midst of a pan troop.

 There were several dozen, startled and blinking. He yelled inco­ herently, wondering how Ipan would signal to them.

 The nearest large male turned, bared teeth, and shrieked angrily. The entire pack took up the call, whooping and snatching up sticks and rocks, throwing them at Ipan. A pebble hit him on the chin, a branch on the thigh. He fled, Sheelah already a few steps ahead of him.

 The raboons came charging across the clearing. In their claws they held small, sharp stones. They looked big and solid, but they slowed at the barrage of screeches and squawks coming from the trees.

 Ipan and Sheelah burst out into the grass of the clearing and the pans came right after them. The raboons skidded to a halt.

 The pans saw the raboons, but they did not stop or even slow. They still came after Ipan and Sheelah with murderous glee.

 The raboons stood frozen, their claws working uneasily.

 Hari realized what was happening and picked up a branch as he ran, calling to Sheelah. She saw and copied him. He ran straight at the raboons, waving the branch. It was an awkward, twisted old limb, useless, but it looked big. Hari wanted to seem like the ad­ vance guard of some bad business.

 In the rising cloud of dust and general chaos the raboons saw a large party of enraged pans emerging from the forest. They bolted.

 Squealing, they ran at full stride into the far trees.

 Ipan and Sheelah followed, running with the last of their strength. By the time Ipan reached the first trees, he looked back and the pans had stopped halfway, still screeching their vehemence.

 He signed to Sheelah, Go. They cut away at a steep angle, heading uphill.

 19.

 Ipan needed food and rest—if only to stop his heart from lurching at every minor sound. Sheelah and Ipan clutched each other, high in a tree, and crooned and petted.

 Hari needed time to think. Autoservers were keeping their bodies alive at the station. Dors’ tiktok would defend the locks, but how long would a security officer take to get around that?

 It would be smart to let them stay out here, in danger, saying to the rest of the staff that the two odd tourists wanted a really long immersion. Let nature take its course.

 His thinking triggered jitters in Ipan, so he dropped that mode. Better to think abstractly. There was plenty out here that needed understanding.

 He suspected that the ancients who planted pans and gigantelope and the rest here had tinkered with the raboons, to see if they could turn a more distant primate relative into something like humans. A perverse goal, it seemed to Hari, but believable. Scientists loved to tinker.

 They had gotten as far as pack-hunting, but raboons had no tools beyond crudely edged stones, occasionally used to cut meat once they had brought it down.

 In another few million years, under evolution’s grind, they might be as smart as pans. Who would go extinct then?

 At the moment he didn’t much care. He had felt real rage when the pans—his own kind!—had turned against them, even when the raboons came within view. Why?

 He worried at the issue, sure there was something here he had to understand. Psychohistory had to deal with such basic, funda­ mental impulses. The pans’ reaction had been uncomfortably close to myriad incidents in human history.

 Hate the Stranger.

 He had to fathom that murky truth.

 Pans moved in small groups, disliking outsiders, breeding mostly within their modest circle of a few dozen. This meant any genetic trait that emerged could pass swiftly into all the members, through inbreeding. If it helped the band survive, the rough rub of chance would select for that band’s survival. Fair enough.

 But the trait had to be undiluted. A troop of especially good rock throwers would get swallowed up if they joined a company of several hundred. Contact would make them breed outside the ori­ ginal small clan. Outbreeding: their genetic heritage would get watered down.

 Striking a balance between the accidents of genetics in small groups, and the stability of large groups—that was the trick. Some lucky troop might have fortunate genes, conferring traits that fit the next challenge handed out by the ever-altering world. They would do well. But if those genes never passed to many pans, what did it matter?

 With some small amount of outbreeding, that trait got spread into other bands. Down through the strainer of time, others picked up the trait. It spread.

 This meant it was actually helpful to develop smoldering animos­ ity to outsiders, an immediate sense of their wrongness. Don’t breed with them.

 So small bands held fast to their eccentric traits, and some prospered. Those lived on; most perished. Evolutionary jumps happened faster in small, semi-isolated bands which outbred slightly. They kept their genetic assets in one small basket, the troop. Only occasionally did they mate with another troop—often, through rape.

 The price was steep: a strong preference for their own tiny lot.

 They hated crowds, strangers, noise. Bands of less than ten were too vulnerable to disease or predators; a few losses and the group failed. Too many, and they lost the concentration of close breeding. They were intensely loyal to their group, easily identifying each other in the dark by smell, even at great distances. Because they had many common genes, altruistic actions were common.

 They even honored heroism—for if the hero died, his shared genes were still passed on through his relatives.

 Even if strangers could pass the tests of difference in appearances, manner, smell, grooming, even then, culture could amplify the ef­ fects. Newcomers with different language or habits and posture would seem repulsive. Anything that served to distinguish a band would help keep hatreds high.

 Each small genetic ensemble would then be driven by natural selection to stress the noninherited differences, even arbitrary ones, dimly connected to survival fitness…and so they could evolve cul­ ture. As humans had.

 Diversity in their tribal intricacies avoided genetic watering down. They heeded the ancient call of aloof, wary tribalism.

 Hari/Ipan shifted uneasily. Midway through his thinking, the word they had come in Hari’s thinking to mean humans as well as pans. The description fit both.

 That was the key. Humans fit into the gigantic Empire despite their innate tribalism, their panlike heritage. It was a miracle!

 But even miracles called out for explanation. Pans could be useful models for the gentry and the vast citizenry, the two classes encour­ aged to breed.

 Yet how could the Empire possibly have kept itself stable, using such crude creatures as humans?

 Hari had never seen the issue before in such glaring, and hum­ bling, light.

 And he had no answer.

 20.

 They moved on in spite of the blunt, deep unease of their pans.

 Ipan smelled something that sent his eyes darting left and right. With the full tool kit of soothing thoughts and the subtle tricks he had learned, Hari kept him going.

 Sheelah was having more trouble. The female pan did not like laboring up the long, steep gullies that approached the ridge line. Gnarled bushes blocked their way and it took time to work around them. Fruit was harder to find at these altitudes.

 Ipan’s shoulders and arms ached constantly. Pans walked on all fours because their immensely strong arms carried a punishing weight penalty. To navigate both trees and ground meant you could optimize neither. Sheelah and Ipan groaned and whined at the soreness that never left feet, legs, wrists, and arms. Pans would never be far-ranging explorers.

 Together they let their pans pause often to crumble leaves and soak up water from tree holes, a routine, simple tool use. They kept sniffing the air, apprehensive.

 The smell that disturbed both pans got stronger, darker.

 Sheelah went ahead and was the first over the ridge line. Far below in the valley they could make out the rectangular rigidities of the Excursion Station. A flyer lifted from the roof and whispered away down the valley, no danger to them.

 He recalled what seemed a century ago, sitting on the verandah there with drinks in hand and Dors saying, If you stayed on Trantor you might be dead. Also, if you didn’t stay on Trantor…

 They started down the steep slope. Their pans’ eyes jerked at every unexpected movement. A chilly breeze stirred the few low bushes and twisted trees. Some had a feathered look, burnt and shattered by lightning. Air masses driven up from the valleys fought along here, the brute clash of pressures. This rocky ridge was far from the comfortable province of pans. They hurried.

 Ahead, Sheelah stopped.

 Without a sound, five raboons rose from concealment, forming a neat half circle around them.

 Hari could not tell if it was the same pack as before. If so, they were quite considerable pack hunters, able to hold memory and purpose over time. They had waited ahead, where there were no trees to climb.

 The raboons were eerily quiet as they strode forward, their claws clicking softly.

 He called to Sheelah and made some utterly fake ferocious noises as he moved, arms high in the air, fists shaking, showing a big profile. He let Ipan take over while he thought.

 A raboon band could certainly take two isolated pans. To survive this they had to surprise the raboons, frighten them.

 He looked around. Throwing rocks wasn’t going to do the trick here. With only a vague notion of what he was doing, he shuffled left, toward a tree that had been splintered by lightning.

 Sheelah saw his move and got there first, striding energetically. Ipan picked up two stones and flung them at the nearest raboon. One struck on the flank but did no real harm.

 The raboons began to trot, circling. They called to each other in wheezing grunts.

 Sheelah leaped on a dried-out shard of the tree. It snapped. She snatched it up and Hari saw her point. It was as tall as she was and she cradled it.

 The largest raboon grunted and they all looked at each other.

 The raboons charged.

 The nearest one came at Sheelah. She caught it on the shoulder with the blunt point and it squealed.

 Hari grabbed a stalk of the shattered tree trunk. He could not wrench it free. Another squeal from behind him and Sheelah was gibbering in a high, frightened voice.

 It was best to let the pans release tension vocally, but he could feel the fear and desperation in the tones and knew it came from Dors, too.

 He carefully selected a smaller shard of the tree. With both hands he twisted it free, using his weight and big shoulder muscles, cracking it so that it came away with a point.

 Lances. That was the only way to stay away from the raboon claws. Pans never used such advanced weapons. Evolution hadn’t gotten around to that lesson yet.

 The raboons were all around them now. He and Sheelah stood back to back. He barely got his feet placed when he had to take the rush of a big, swarthy raboon.

 The raboons had not gotten the idea of the lance yet. It slammed into the point, jerked back. A fearsome bellow. Ipan wet himself with fear, but something in Hari kept him in control.

 The raboon backed off, whimpering. It turned to run. In midstride it stopped. For a long, suspended moment the raboon hesit-ated—then turned back toward Hari.

 It trotted forward with new confidence. The other raboons watched. It went to the same tree Hari had used and, with a single heave, broke off a long, slender spike of wood. Then it came toward Hari, stopped, and with one claw held the stick forward. With a toss of its big head it looked at him and half turned, putting one foot forward.

 With a shock Hari recognized the swordplay position.

 Vaddo had used it. Vaddo was riding this raboon.

 It made perfect sense. This way the pans’ deaths would be quite natural. Vaddo could say that he was developing raboon riding as a new commercial application of the same hardware that worked for pan riding.