Kauffman is arguing that biological uses cannot be deduced in advance: lens crystallins from ordinary enzymes, thermoregulatory bumps on dinosaurs into flight feathers. The swim bladder is his standing example, because once a fish has a sac of air and water it is also, unintentionally, somewhere a worm can live. He uses it against the idea that evolution's openness can be specified ahead of time, which is where he says machines get stuck.