question:  What is ironic about Taphetta's contempt for mating among species?
context: 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. 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. "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. 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. "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 !" "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. It would do no good to explain that Taphetta wasn't a worm, that his evolution had taken a different course, but that he was in no sense less complex than Man. It was a paradox that some biologically higher humans hadn't developed as much as lower races and actually weren't prepared for the multitude of life-forms they'd meet in space.
output:  Taphetta is biologically unable to mate with other species
options:  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