In many songbird species, individuals reared in acoustic isolation still develop a rudimentary song, but one that is abnormal in its finer structure; only birds exposed to a tutor during a sensitive early window acquire the species-typical form. Researchers long read this as evidence that the template for song is largely innate and that experience merely fine-tunes it. A dissenting group notes, however, that the 'isolate' song, though produced without a model, is not random: it drifts, over generations of isolated birds, toward the normal song. If a purely innate template governed development, they argue, such directional recovery across generations would be difficult to explain.