 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.] "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. 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. "But there are other worlds in which humans who were there before the Stone Age aren't related to anything else there. When we project back into time those star systems on which humans existed prior to space travel, we get a certain pattern. "And whereas there are humans who are relatively near and not fertile, they can always mate with those they were adjacent to two hundred thousand years ago !" And, of course, if it were a fast-moving star, it might be completely out of the field of our exploration. "I had other plans, but I can't evade professional obligations, and an emergency such as this should cancel out any previous agreements.
 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