 What is ironic about Taphetta's contempt for mating among species?
In repose, Taphetta the Ribboneer resembled a fancy giant bow on a package. Taphetta rattled the head fronds together in a surprisingly good imitation of speech. "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 ! "It is impressive," admitted Taphetta. "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. Taphetta rustled his speech ribbons quizzically. 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. "And so, to account for the unique race that can interbreed across thousands of light-years, you've brought in the big ancestor," commented Taphetta dryly. "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. Still, Taphetta the Ribboneer was an experienced pilot and could be very useful. The theory is that humans who can mate with each other were once physically close. When we project back into time those star systems on which humans existed prior to space travel, we get a certain pattern. Taphetta rustled. "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 !" "The adjacency mating principle. Anyway, non-humans weren't trained in the fine distinctions that men made among themselves. "I'm complimented that you like our contract so well," said Taphetta, "but I really must have our own unsimplified version. "You can read it if you want," offered Taphetta.
 Taphetta is biologically unable to mate with other species
 Taphetta can only survive if they mate with another species  Taphetta is actually jealous about other species' ability to intermix  Taphetta is likely a result of mating among species  Taphetta is biologically unable to mate with other species