Mordan smiled. "The fighters survived. That is the final test. Natural selection goes on always, regardless of conscious selection."

"Wait a minute," demanded Hamilton. "That doesn't check. According to that, we should have lost the Second Genetic War. Their 'mules' were certainly willing to fight."

"Yes, yes," Mordan agreed, "but I did not say that combativeness was the only survival characteristic. If it were, the Pekingese dog would rule the earth. The fighting instinct should be dominated by cool self-interest. Why didn't you shoot it out with me last night?"

"Because there was nothing worth fighting about."

"Exactly. The geneticists of the Great Khan made essentially the same mistake that was made three hundred years earlier; they thought they could monkey with the balance of human characteristics resulting from a billion years of natural selection and produce a race of supermen. They had a formula for it-efficient specialization. But they neglected the most obvious of human characteristics.

"Man is an unspecialized animal. His body, except for its enormous brain case, is primitive. He can't dig; he can't run very fast; he can't fly. But he can eat anything and he can stay alive where a goat would starve, a lizard would fry, a bird freeze. Instead of special adaptations he has general adaptability-"

The Empire of the Great Khans was a reversion to an obsolete form-totalitarianism. Only under absolutism could the genetic experiments which bred homo proteus have been performed, for they required a total indifference to the welfare of individuals.

Gene selection was simply an adjunct to the practices of the imperial geneticists. They made use also of artificial mutation, by radiation and through gene-selective dyes, and they practiced endocrine therapy and surgery on the immature zygote. They tailored human beings-if you could call them that-as casually as we construct buildings. At their height, just before the Second Genetic War, they bred over three thousand types including the hyperbrains (thirteen sorts), the almost brainless matrons, the clever and repulsively beautiful pseudo-feminine freemartins, and the neuter "mules."

We tend to identify the term mule with fighters, since we knew them best, but in fact, there was a type of mule for every sort of routine job in the Empire. The fighters were simply those specialized for fighting.

And what fighters! They needed no sleep. They had three times the strength of ordinary men. There is no way to compare their endurance since they simply kept on going, like well designed machines, until disabled. Each one carried fuel-"fuel" seems more appropriate than "food"-to last it for a couple of weeks, and could function beyond that time for at least another week.

Nor were they stupid. In their specialization their minds were keen. Even their officers were mules, and their grasp of strategy and tactics and the use of scientific weapons was masterly. Their only weakness lay in military psychology; they did not understand their opponents-but men did not understand them; it worked both ways.

The basic nature of their motivation has been termed a "substitute for sex sublimation," but the tag does not explain it, nor did we ever understand it. It is best described negatively by saying that captured mules became insane and suicided in not over ten days time, even though fed on captured rations. Before insanity set in they would ask for something called vepratoga in their tongue, but our semanticists could discover no process referent for the term.

They needed some spark that their masters could give them, and which we could not. Without it they died.

The mules fought us-yet the true men won. Won because they fought and continued to fight, as individuals and guerilla groups. The Empire had one vulnerable point, its co-ordinators, the Khan, his satraps and administrators. Biologically the Empire was a single organism and could be killed at the top, like a hive with a single queen bee. At the end, a few score assassinations accomplished a collapse which could not be achieved in battle.

No need to dwell on the terror that followed the collapse. Let it suffice that no representative of homo proteus is believed to be alive today. He joined the great dinosaurs and the sabre-toothed cats.

He lacked adaptability.

"The Genetic Wars were brutal lessons," Mordan added, "but they taught us not to tamper casually with human characteristics. If a characteristic is not already present in the germ plasm of the race we don't attempt to put it in. When natural mutations show up, we leave them on trial for a long time before we attempt to spread them around through the race. Most mutations are either worthless, or definitely harmful, in the long run. We eliminate obvious disadvantages, conserve obvious advantages; that is about all. I note that the backs of your hands are rather hairy, whereas mine are smooth. Does that suggest anything to you?"

"No."

"Nor to me. There appears to be no advantage, one way or the other, to the wide variations in hair patterns of the human race. Therefore we leave them alone. On the other hand-have you ever had a toothache?"

"Of course not."

"Of course not. But do you know why?" He waited, indicating that the question was not rhetorical.

"Well... it's a matter of selection. My ancestors had sound teeth."

"Not all of your ancestors. Theoretically it would have been enough for one of your ancestors to have naturally sound teeth, provided his dominant characteristics were conserved in each generation. But each gamete of that ancestor contains only half of his chromosomes; if he inherited his sound teeth from just one of his ancestors, the dominant will be present in only half of his gametes.

"We selected-our predecessors, I mean-for sound teeth. Today, it would be hard to find a citizen who does not have that dominant from both his parents. We no longer have to select for sound teeth. It's the same with color blindness, with cancer, with hemophilia, with a great many other heritable defects-we selected and eliminated them, without disturbing in any way the ordinary, normal, biologically commendable tendency for human beings to fall in love with other human beings and produce children. We simply enabled each couple to have the best children of which they were potentially capable by combining their gametes through selection instead of blind chance."

"You didn't do that in my case," Hamilton said bitterly. "I'm a breeding experiment."

"That's true. But yours is a special case, Felix. Yours is a star line. Every one of your last thirty ancestors entered voluntarily into the creation of your line, not because Cupid had been out with his bow and arrow, but because they had a vision of a race better than they were. Every cell in your body contains in its chromosomes the blueprint of a stronger, sounder, more adaptable, more resistant race. I'm asking you not to waste it."

Hamilton squirmed uncomfortably. "What do you expect me to do? Play Adam to a whole new race?"

"Not at all. I want you to perpetuate your line."

Hamilton leaned forward. "Gotcha!" he said. "You're trying to do what the Great Khans did. You're trying to separate out one line and make it different from the rest... as different as we are from the control naturals. It's no good. I won't have it. "

Mordan shook his head slowly. "Wrong on both counts. We intend to follow a process similar to that used to get sound teeth. Have you ever heard of Deaf Smith County?"

"No."

"Deaf Smith County, Texas, was a political subdivision of the old United States. Its natives had sound teeth, not by inheritance, but because of the soil. It gave them a diet rich in phosphates and fluorides. You can hardly appreciate the curse of dental caries in those days. Teeth actually rotted in the head, and were the cause of a large part of the continual sicknesses of the time. There were nearly a hundred thousand technicians in North America alone who did nothing but remove and repair diseased teeth-even at that, four fifths of the population had no such help. They simply suffered and died, with their rotten teeth poisoning their whole bodies."