"Minerva's moon fell toward the Sun. Lunarians were still alive on the moon. It came near to Earth and was captured. It became Earth's moon, and still is now."

"The Lunarians who were alive must have traveled to Earth," ZORAC interrupted. "During the time that followed, they increased their numbers. Earthmen have evolved from Lunarians. That is why they look the same. I can compute no alternative. Am I right?"

"Yes, you're right, ZORAC." Hunt shook his head in admiration. With hardly any data at all to go by, the machine had unerringly arrived at the same conclusion that had taken the scientists of Earth more than two years to piece together, after some of the most vigorous argument and dissent for many decades. "At least, we believe that that is right. We cannot prove it conclusively."

"Sorry. Conclusively?"

"Finally. . . for certain."

"I see. I reason that the Lunarians must have traveled to Earth in spaceships. They must have taken machines and other things. I suggest that Earthmen should look for these things on the surface of the Earth. This would prove what you believe is true. My conclusion is that you haven't tried, or alternatively you have tried but have not succeeded."

Hunt was flabbergasted. Had ZORAC been around two years earlier the whole puzzle would have been solved in a week.

"Have you been talking to an Earthman called Danchekker?" he asked.

"No. I have not met the name. Why?"

"He is a scientist and reasons the same things as you. We have not yet found any traces of things that the Lunarians might have brought with them. Danchekker predicts that such things will be found one day."

"Did the Earthmen not know where they had come from?" ZORAC inquired.

"Not until very recently. Before that it was believed that they evolved only on Earth."

"The life kinds that they evolved from on Minerva had been taken from Earth by the Ganymeans. The same life kinds were left to live on Earth also.

"The Lunarians who did not die and went to Earth were an advanced race. The Earthmen of now did not know of them until recently. Therefore they had forgotten where they came from. I reason that there must have been very few Lunarians who did not die. They became unadvanced and forgot their knowledge. After fifty thousand years they became advanced again, but they had forgotten the Lunarians. As they found new knowledge, they would see remains of life kinds from many years ago everywhere on Earth. They would see the sameness as their own life kind. They would reason that they evolved on Earth. Recently Earthmen have discovered Lunarians and Ganymeans. Now they have deduced the true events. Otherwise they would not be able to explain why Lunarians looked the same as them."

ZORAC had the whole thing figured out. Admittedly the machine had been able to start out with a number of key items of information that had taken Hunt and his colleagues a long time to uncover, but nevertheless it was a staggering piece of logical analysis.

Hunt was still marveling at the achievement when ZORAC spoke again. "I still do not know why the Lunarians destroyed Minerva."

"They didn't intend to," Hunt explained. "There was a war on Minerva. We believe the planet's crust was thin and unstable. The weapons used were very powerful. The planet exploded in the process."

"Sorry. War? Crust? Weapon? Don't follow."

"Oh God. . ." Hunt groaned. He paused to select and light a cigarette from a pack lying on the locker. "The outside of a planet is cold and hard--near the surface. That's its crust."

"Like a skin?"

"Yes, but brittle . . . it breaks into pieces easily."

"Okay."

"When many people fight in large groups, that's war."

"Fight?"

"Oh hell . . . violent action between one group of people and another group. When they organize themselves to kill."

"Kill what?"

"The other group of people."

ZORAC gave one distinct impression of confusion. For a second the machine seemed to be having difficulty in believing its microphone.

"Lunarians organized themselves to kill other Lunarians," it said, slowly and carefully as if anxious not to be misunderstood. "They did this deliberately?"

The turn of conversation had caught Hunt somewhat unprepared. He began to feel uneasy and even a little embarrassed, like a child being insistently cross-examined over some transgression that it would sooner forget.

"Yes," was all he could manage.

"Why did they wish to do such a thing?" The emotional inflection was there again, now registering undisguised incredulity.

"They fought because . . . because . . ." Hunt wrestled for something to say. The machine, it seemed, had no comprehension whatsoever of such matters. What way was there to summarize the passions and complexities of millennia of history in a few sentences? "To protect themselves . . . to defend their own group from other groups. . ."

"From other groups who were organized to kill them?"

"Well, the matter is very complicated . . . but yes, you could say that."

"Then logically the same question still applies--why did the other groups wish to do such things?"

"When one group made another group angry about something or when two groups both wanted the same thing, or when one group wanted another group's land, maybe . . . sometimes they would fight to decide." What he was saying didn't seem an adequate explanation, Hunt admitted to himself, but it was the best he could do. A short silence ensued; even ZORAC, it seemed, had to think hard about this one.

"Did all the Lunarians have brain problems?" it asked at last, having evidently deduced what it considered the most probable common factor.

"They were naturally a very violent race, we believe," Hunt replied. "But at the time they lived, they faced the prospect of extinction--all dying out. Minerva was freezing all over fifty thousand years ago. They wanted to go to a warmer planet to live. We think they wanted to go to Earth. But there were many Lunarians, few resources, and little time. The situation made them afraid and angry. . . and they fought."

"They killed each other to prevent them from dying? They destroyed Minerva to protect it from freezing?"

"They didn't intend to do such a thing," Hunt said again.

"What did they intend?"

"I suppose they intended that the group that was left after the war would go to Earth."

"Why couldn't all groups go? The war must have needed resources that would have been used better for other things. All Lunarians could have used their knowledge. They wanted to live but did everything to make certain that they would not. They had brain problems." The tone of ZORAC's final pronouncement was definite.

"All this was not something they had planned deliberately. They were driven by emotions. When men feel strong emotions, they do not always do the most logical things."

"Men . . . Earthmen . . . ? Earthmen feel strong emotions too, that make them fight like the Lunarians did?"

"Sometimes."

"And Earthmen make wars too?"

"There have been many wars on Earth, but there have been none for a long time."

"Do the Earthmen wish to kill the Ganymeans?"

"No! No . . . of course not. There is no reason . . ." Hunt protested violently.

"There can never be a reason," ZORAC stated. "The Lunarians had no reason. The things that you said are not reasons since they do the opposite to what is wanted--so they are not reasonable. The Earthmen must have evolved brain problems from the Lunarians. Very sick."

Danchekker had theorized that the extraordinary aggressiveness and powers of determination exhibited by Man, compared to other terrestrial species, had originated as a mutation among the anthropoids left on Minerva after the decline of the Ganymeans. It had accounted for the startling rapidity of the emergence and development of the Lunarian civilization, which had attained spaceffight while the most advanced species on Earth were represented only by primitive stone-working cultures. As ZORAC had surmised, this formidable Lunarian trait had indeed been passed on to their terrestrial descendants (although becoming somewhat diluted in the process), and had in turn constituted the most potent factor in the subsequent emergence and rise of the human race. Could that trait after all turn out to be the unique aberration that Danchekker had sometimes speculated?