 The scene depicting the two pests interacting is symbolic of:
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. That's what happened on Earth; when Man arrived, there was actually a manlike creature 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." 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. This is one arm of it as it is today and here are the human systems." And while stars in a given region tend to remain together, there's also a random motion. They were spaced at fairly equal intervals along a regular curve, a horseshoe loop that didn't close, though if the ends were extended, the lines would have crossed.
 The lengths all species will go to in order to surpass one another or protect their own status
 The potential danger that could result if intermixing becomes prevalent and social stratification becomes impossible  The reality that 'playing dead' is the best strategy for managing other threatening species who use more overt power to retain superiority  The lengths all species will go to in order to surpass one another or protect their own status  Taphetta's actualized fear that humans will use germ plasm to become biologically superior to his race