Of course, proof of inhumanity was seldom a problem. Most alien life forms were obviously alien. But there were a few--like the Lani--where similarities were so close that it was impossible to determine their status on the basis of morphology alone. And so the Humanity Test had come into being. Essentially it was based upon species compatibility--on the concept that like can interbreed with like. Tests conducted on every inhabited world in the Brotherhood had proven this conclusively. Whatever changes had taken place in the somatic characteristics of mankind since the Exodus, they had not altered the compatibility of human germ plasm. Man could interbreed with man--aliens could not. The test was simple. The results were observable. And what was more important, everyone could understand it. No definition of humanity could be more simple or direct. But was it accurate? Like other Betans, Kennon wondered. It was--so far--probably. The qualifying phrases were those of the scientist, that strange breed that refuses to accept anything as an established fact until it is proven beyond a shadow of a doubt. After all, the human race had been spaceborne for only six thousand years--scarcely time for any real differences to develop. But physical changes had already appeared--and it would only be a question of time before these would probably be followed by genetic changes. And in some groups the changes might be extensive enough to make them genetic strangers to the rest of humanity. What would happen then? No one knew. Actually no one bothered to think about it except for a few far-seeing men who worried as they saw. Probably. Might. Possibly. If. Four words. But because of them the Betans were slowly withdrawing from the rest of humanity. Already the radiations of Beta’s variant-G sun had produced changes in the population. Little things like tougher epidermis and depilation of body hair--little things that held alarming implications to Beta’s scientists, and to Beta’s people. Not too many generations hence a Betan outside his home system would be a rarity, and in a few millennia the Betan system itself would be a closed enclave peopled by humans who had deviated too far from the basic stock to mingle with it in safety. Of course, the Brotherhood itself might be changed by that time, but there was no assurance that this would happen. And mankind had a history of dealing harshly with its mutants. So Beta would play it safe.