"They were originally about three feet high. They've been deliberately bred to diminish their size, so that more of them might be supported at a given standard of nutrition. But overpopulation has always been a problem nonetheless, and has driven them on continually to look for new planets. That's why they're so interested in our system."
"And that," said Arthur, "is also why, once we've handed over everything we have, they'll exterminate us, and proceed to colonize as if they had never signed an agreement."
"Possibly."
"You say that very calmly, dad. As if the extinction of the race meant nothing to you."
"Because we have no choice. However, I was going to tell you about their weaknesses. These derive from their lack of height. As the Hops shrank in size from generation to generation, they became shorter-lived. At present, they live on an average only five of our years, of which at most three can be considered years of maturity, with full adult powers.
"They might have done something about it originally by changing the direction of their own evolution. But the shorter their lives, the less pressing the problem of overpopulation. And at a time when they were engaged in continual wars, they preferred to have replacements made as quickly as possible—which meant a shorter period of infancy, and again a shorter total life.
"Their ability to mature quickly also made for greater vigor as soldiers, and involved no lengthy old age during which the injured veterans had to be taken care of. Later on, when the process had gone further than they liked, they tried to reverse it, and couldn't. It was biologically difficult, and politically impossible. It would have intensified all the problems of overpopulation, and started a civil war. They're stuck with their five-year lives.
"The consequences have been tremendous. During the three years of adulthood it is no longer possible to master any reasonably broad and complicated field of knowledge, let alone advance it. Despite their application of what had previously been learned in psychology, and their attempt to substitute machine calculation for brainwork as much as possible, they are no longer able to train any large body of research scientists. Instead of developing, their science has deteriorated. Entire branches they had formerly mastered have now been relegated to the museums and libraries. They don't have time for philosophy or logic, or other such luxuries. All their science is, one way or another, military science. They hang desperately onto that."
"And this deterioration is continuing?"
"Steadily. It would take us a hundred years to reach their present attainments in military nucleonics and biologics. But they're going backward as rapidly as we move forward. That's why I told you before that fifty years might be enough."