“What do you expect to find?” Mrs. Rhodes inquired, not for the first or second time.

  “Look—a Dinotherium hunt!”

  She looked automatically before realizing that this was another guided vision—and another evasion. The old woman saw so clearly into the living past that it was contagious. “Dino—is that an animal? Or a large reptile?” Dinotherium was mammalian. Foraging in the swampy jungle, it sought no particular conflict with other creatures, and few bothered it. Like an elephant with tusks pointing straight down, and with an abbreviated trunk, it was the largest creature of this valley, and could well afford to be peaceful. This one had strayed onto solid ground, oblivious to danger.

  Behind it manlike forms approached. Dinotherium hooked another leafy branch down, unconcerned though he was aware of the intrusion. His great tusks held the branch in place while his trunk picked it over.

  The men came closer, making vocal sounds rather like the barking of canines. Dinotherium, annoyed, moved along a short distance, seeking to leave them behind. But they followed, clamoring more loudly, hemming him in from back and side.

  Dinotherium became moderately alarmed, and ceased browsing. These gesticulating bipeds could hardly harm him, but their proximity and persistence were unnatural. He ran smoothly, desiring only to free himself of the strange situation so he could finish his browse. He bore left, away from the concentration of Australopithecines.

  Suddenly he realized where he was. Ahead was a deep sharp gully, the product of seasonal flash floods, whose tumbling sides were treacherous for a creature of his size. He veered farther left—and encountered more men.

  The choice was between the gully and the men, now that he was fleeing. The gully at least was a known danger. But—there was a gap in the line, an easy escape. Dinotherium charged at it.

  The noise increased. Men ran to cut him off, chattering. But the nearest one stood indecisively, failing to act in time. Dinotherium plunged through the space and headed for the swamp where men would be foolish to follow.

  “He got away,” Mrs. Rhodes said, relieved.

  “Because one man did not follow instructions,” Miss Concher said. “The leader plainly hooted at the fool to close it up, but he didn’t comprehend in time.”

  “Yes, I saw that. But how does it relate to the trail we are following now? This is no Dinotherium hunt.” This time she did not intend to be put off.

  The blind eyes focused on her disconcertingly. “How much do you think that tribe lost, because of the failure of that one member?”

  “I would imagine they went hungry—at least until they could set up another hunt.”

  “Hunger wasn’t very funny in those days, was it?”

  “Of course not,” Mrs. Rhodes agreed, visualizing a primitive camp, the children bawling, the women standing glumly. “What did they do to that man who—”

  “The leader banished him from the tribe, so of course he soon perished. If you’re going to hunt Dinotherium, you can’t afford any lapses in your organization.”

  “Also, the others were mad, I’m sure. Had to take it out on someone. But how does that—”

  “Communication,” Miss Concher said. “Now Australopithecus has a compelling reason to select for that single trait Note that—the first artificial selection in the history of life on Earth, and for a nonphysical trait. He can’t tolerate tribesmen who can’t or won’t respond to spoken instructions, even if these only take the form of imperative barking. The groups with dumb members will fall on hard times, and their children will starve, while those who are selective will become fine hunting units. They will be capable of driving Dinotherium into the gully and stoning him to death there while he stumbles in the steep sand, and they will eat well and prosper. Communication is the key—the small mouth put to the uses of survival!”

  “I concede that,” Mrs. Rhodes said, both enlightened and annoyed. “But what—”

  “Once you’re on that treadmill, you have to continue. You need the big game to feed your increasing numbers, for squirrels and sparrows won’t feed an entire tribe for long, and certainly not wild fruit. You become dependent on organization, on the specialization that is the hunt. And you begin to contest with neighboring tribes for the best hunting territory, staking it out, and so your communication is now employed man-against-man. That’s a rough game, and if you quit you die. Today an army is helpless when its communications break down. Your size increases and your brain expands, as it must to handle the burgeoning linguistic concepts required to define an effective campaign. Barks meaning ‘run’ ‘stop’ and ‘kill’ give way to subtler sounds meaning ‘run faster’ ‘stop over there’ and ‘kill on command only.’ And finally you are not just Australopithecus, you are Homo Erectus. An animal with the single specialized organ so harshly selected for: the brain.”

  Mrs. Rhodes refused to be diverted. “This trail—”

  “I believe,” Miss Concher said gently, “that it was not mere coincidence or fleeting convenience that started Australopithecus along the demanding highway of verbal communication. The odds against this seem prohibitive. Some outside agency instructed him. Something forcibly directed him to speak, or somehow arranged it so that he had to communicate in order to survive at all. Something that knew where this process would lead. And that is what we are sniffing out now—that alien influence that shaped us into mastery.”

  At last Mrs. Rhodes saw the point. If somebody—somerizing, for there could have been no true men then—if some agency had come to show potential man the route to success—

  Man had a debt going back two million years.

  And now two women, one middle-aged and the other old, were belatedly on the trail of that visitation, that phenomenally important influence. What would they find?

  Miss Concher nodded. “It’s a little frightening, isn’t it? We may not appreciate the truth one bit—but can there be any question of turning back now?”

  This close to the answer to the riddle of man’s progress? No, of course they could not turn back.

  l

  Down the Great Rift Valley they traveled, sniffing out the ancient trace. The natives generally ignored them. What harm could two crazy old women do, with their truckful of junk? They skirted Lake Tanganyika and traversed the length of Lake Nyasa, and the trail continued. At last they stood at the mouth of the Zambeizi River, and the trace vanished.

  They stood on the shore and looked eastward, Mrs. Rhodes’ live eyes seeing no more than Miss Concher’s dead ones. Their gruelling weeks of travel and drilling had come to an unhappy halt, for the water held no scent.

  “No,” Miss Concher said. “This is merely a hurdle. It can not end here.” But for once her words lacked conviction. She had been an energumen until this moment, expending energy at a cheerful but appalling rate; now she was an old woman who could not find her knitting.

  “A sea-creature?” Mrs. Rhodes suggested, embarrassed by her companion’s weakness. She tried to envision a credible object, but without Miss Concher’s guidance it manifested as a parody: an ancient octopus struggling rheumatically out of the depths, donning sunglasses and marching up the Rift to the sound of fife and drum to instruct Australopithecus. Ridiculous!

  “Unlikely,” Miss Concher said. But her bulldog mind was working again, after its hesitation. “Could have been based on the sea-floor, though. Or floating on the surface. The sea is an obvious highway for civilized species—check the map.”

  Mrs. Rhodes gladly did so. “It’s a long coast line. Funny that they should come to this particular place, then make a thousand mile journey overland, when they could have landed so much closer to Lake Victoria . . .” She paused. “Unless they crossed directly from Madagascar—”

  “My diagnosis exactly!” Had it been—or was Miss Concher trying to conceal her lapse? “Let’s rent a boat.”

  What did it matter? They had a mission once more.

  The crossing was not so simple as merely “renting a boat,” but two weeks later they had negotiated the physical and political hazards and were driving their truck along the west coast of Madagascar. In another two they had spotted the trace again. The trek resumed: east, into the heart of the huge island.

  The palms of the shoreline gave way to rice fields and island-like hills and occasional thatch-roofed earthern houses. Mrs. Rhodes looked up one dusk to meet a pair of large eyes. “Something’s watching us,” she whispered, startled.

  “Describe it,” Miss Concher said, unruffled.

  She peered at the creature, beginning to make it out in the shadow. “Small, bushy-tailed, head rather like a fox—but it has monkey-feet, and it’s clinging to a branch.”

  “Lemur,” Miss Concher said. “Madagascar is their homeland. The few species extant today are a poor remnant of those that ranged the world in past times.”

  “Not dangerous, then,” Mrs. Rhodes said, relaxing.

  “Not now. One type, Megaladapis, was larger than a gorilla—in fact, was the largest primate known. And another extinct Lemuridae, Archae demur, may have been remarkably cunning, if we are to judge by the precocious development of the temporal lobe during the—”

  “You’re leaving me behind, I’m afraid,” Mrs. Rhodes cut in gently. The old lady smiled, making no secret of her pleasure in doing just that. It had become a kind of game. The fact was that Mrs. Rhodes, a skilled nurse, was not confused by anatomical allusions. She merely wished to abbreviate a developing lecture.

  A modem city whose name they ignored obliterated a Segment of the trail, but they resumed operations on the far side. Now they crossed parched savanna dotted with palms. “On this island, in historic times,” Miss Concher said, “ranged the largest bird ever known: aepyomis.”

  “Now that sounds like a primate!”

  “Its egg weighed twenty pounds, and a mature bird up to half a ton. Man wiped it out, of course.”

  “You don’t have a very high opinion of man, do you.”

  “That’s why I’m single.” But Miss Concher smiled again, too enthusiastic over the progress of the search to be properly cynical. She knew the fauna far better than Mrs. Rhodes did, identifying by description everything from a camouflaged tree-lizard to a forest cuckoo. She also called off a solitary baobab, the tree with the grossly swollen trunk that seemed to have its roots in the air in place of branches, and related an amusing myth about its origin. She knew how to get through a thorny didierea jungle, grown up in recent generations as though to preserve the secrets of the trail.

  They moved on with growing excitement, day by day, until at last the trail debouched into a secluded valley. Repeated soundings verified it: this had been the home, two million years ago, of the mysterious traveler. Today it was wilderness, with only the shy lemurs and curious birds present. Where had man’s ancient tutor gone?

  “If I make out the lay of the land correctly,” Miss Concher said, “there should be buried caves. They may have been occupied, then.”

  Mrs. Rhodes shook her head, marveling anew at the spinster’s talents. If she conjectured buried caves, there would be buried caves.

  They drilled and drilled again, searching. On the third day the bit broke through the wall of a subterranean discontinuity. Its age fell in the correct range and the trace inside was very strong.

  “Now.” Miss Concher said briskly, “we dig.”

  It had to be by hand, since the rig was not geared for wholesale tunneling and in any event the bulldozer technique was hardly appropriate for archaeological excavation. The two women dug a long shallow trench, pausing as often as they had to in deference to sex and age and inexperience. Miss Concher’s contribution was a good deal more than token; her zest drove her ruthlessly. Next day they deepened it, leaving a ramp at one end. As their trench descended into the earth they hauled loads of loam, sand and gravel out in a wheeled sample cart never intended for such crude maneuverings.

  The work was slow, their muscles sore, and both had ugly blisters on their hands despite the heavy gloves. Each day the excavation sank deeper, and their anticipation grew. Down there, perhaps, was tangible evidence of a two-million year old culture—a culture to which man probably owed his present eminence. Blisters were beneath consideration, with the solution to such a mystery so near.

  At last they struck the rocky outer wall of the cave. The drill-hole penetrated a yard of crumbling stone.

  “Either we can keep digging until we come across the natural entrance,” Mrs. Rhodes said, touching the aperture with weary fingers, “or we can break out the sledgehammer. I’m not at all sure my resources will survive either course.”

  “Hammer and chisel will do it,” Miss Concher said, declining to ride with the proffered excuse though she could have done so with grace. Mere stone would not halt her. She demonstrated, flaking off wedges skillfully. “Variation of a technique used in the Oldowan industry for a million years or so, so it will do for us. The stone age had a lot to recommend it.”

  So the old lady knew how to chip stone! The process was slow, but it did promise to get the job done with a minimum of damage to whatever might be in the cave.

  They took turns, the sighted woman laboring clumsily much of the day, and the blind one continuing far into the night. Miss Concher seemed indefatigable and she needed no illumination. Mrs. Rhodes, weary to the marrow, became too dull to marvel further at the resources of her companion. Most women of that age would be crocheting harmlessly in rockers while their grandchildren matured. Purpose animated Miss Concher, provided the motive power—but what would happen once the mission was done? Would there then be a disastrous reckoning?

  But she knew the answer to that. Miss Concher would not collapse; she would find another mission, another trail to follow. In fact it was not the trail that gave her purpose, it was her purpose that revealed the trail, where no one else had thought to look. It was, as the saying went, an education merely to know her.

  And perhaps within this buried cave lay the answer to the start of that purpose. Not only to this immediate trek, but to the inherent motivation of man. The thing that had given a minor hominid the bug for knowledge, two million years ago, and thrust him mercilessly into greatness. The quality that really made Miss Concher the avid scientist she was, and set her species apart from all others. Intellectual motivation.

  Mrs. Rhodes felt nervous goose-pimples rise along her arms despite the heat as the breakthrough point approached. The hole was widening, but Miss Concher refused to risk damaging the interior by rushing. Something was down there, though. Broken pieces where the bit had struck? Bones? Pottery? Weapons? Books? Or something more sinister?

  She slept at last to the tap-tap of Miss Concher’s patient excavation, not attempting to keep up with the woman’s nocturnal energy. It would have been useless to urge her to stop, to rest, to sleep, for Miss Concher lived for this discovery. Better to be ready herself, in case the strain brought serious complications.

  In indeterminate darkness she woke momentarily, still hearing the tap-tap. Regardless of the outcome of this quest, she knew what she was going to do after it was over. She had already learned enough about the heritage of her species to accept some things she had denied before. She had a better marriage than she had supposed, and it was not too late. . . .

  In the morning she discovered that Miss Concher had never returned to the truck to sleep. All was silent.

  She scrambled up in alarm and ran for the gaping trench. She should have stayed up, kept watch . . . if the grand old lady had hurt herself, or collapsed, or—

  She need not have worried. Miss Concher was standing waist-deep in the cave excavation, lifting out objects and using the main trench as a display shelf. Meticulously arranged were a series of irregular objects and portions of an animal skeleton.

  “Miss Concher! Have you been up all night?” But the question was gratuitous and rhetorical.

  The woman lifted her white head, smiling tiredly. “Yes, we have found the answer. We know who started man on his way. The artifacts are conclusive.” She caressed the dirt-encrusted object in her hand. “Mesolithic culture, I would say—shaped tools, but no gardening. They were obviously able to sail on the rivers and ocean, at least with some kind of raft, and to domesticate certain animals—”

  “You know who trained Australopithecus to—”

  “Yes. the hominids were one of their domestics. They recognized in Australopithecus the potential for really effective service, and they took the long view. A few thousand years of selection and training—more than enough to affect the species profoundly—and man was on his way. He even—”

  Mrs. Rhodes was shocked. “You mean man started out as—as a pet, like a dog?”

  “More like a horse, or an elephant. He was trained to obey simple commands, to carry his master, fetch things, and finally to undertake dinotherium hunts under the direction of a few overseers. You see, mainland Africa was too wild for a gentle, civilized species then, as it is today for different reasons. Yet they needed certain commodities such as ivory—”

  Mrs. Rhodes saw a fragment of tusk among the disdinotherium had ever ranged Madagascar. Ivory had to be imported. But how could there have been such a culture on Earth before human civilization arose? “Who—” But she was unable to frame the question properly, afraid of the answer.

  “Why, the Lemuridae, of course. Didn’t I tell you about Archaeolemur, with the almost hominid skull? Here in this cave we have an offshoot new to paleontology, with a comparatively enormous braincase and distinctive configuration. 1,000 cc easily, if my wrinkled old fingers do not deceive me. Easily capable of mesolithic technology, in the circumstances.” She hefted the broken skull. “Look at this marvelous specimen yourself! Plainly derived from Archaeolemur, but the placement of the foramen magnum—”