 What is NOT a reason that a child probably shouldn't read this?
Extensive research did not uncover any evidence that the U.S. copyright on this publication was renewed.] The reaction was not unexpected—non-humans tended to dismiss the data as convenient speculation and nothing more. "There are at least a hundred kinds of humans, each supposedly originating in strict seclusion on as many widely scattered planets. Obviously there was no contact throughout the ages before space travel— and yet each planetary race can interbreed with a minimum of ten others ! "Outside of your own world, there's nothing like your species, except superficially, and that's true of all other creatures, intelligent or not, with the sole exception of mankind. Actually, the four of us here, though it's accidental, very nearly represent the biological spectrum of human development. There's a corresponding span of fertility. Emmer just misses being able to breed with my kind, but there's a fair chance that I'd be fertile with Meredith and a similar though lesser chance that her fertility may extend to Kelburn." "But I thought it was proved that some humans did originate on one planet, that there was an unbroken line of evolution that could be traced back a billion years." "Humans require a certain kind of planet. It's reasonable to assume that, if men were set down on a hundred such worlds, they'd seem to fit in with native life-forms on a few of them. That's what happened on Earth; when Man arrived, there was actually a manlike creature there. "But there are other worlds in which humans who were there before the Stone Age aren't related to anything else there. "Something had to distribute one species so widely and it's not the result of parallel evolution—not when a hundred human races are involved, and only the human race." Man was the most numerous though not always the most advanced—Ribboneers had a civilization as high as anything in the known section of the Milky Way, and there were others—and humans were more than a little feared.
 There was gun violence (with space rays)
 There was casual sexism  There were implications of sex  There was gun violence (with space rays)  There was abuse between partners