London’s research has shown that young birds exposed to a tutor learn easily until they reach the age of sixty-five days. Thereafter, learning ability shuts down, and the bird’s songs remain fixed for life. But young birds isolated from this song exposure can learn well even after sixty-five days. The experience of hearing another bird singing apparently alters the song-learning genes of the learning bird through “epigenetic” effects; in this case, says London, through the action of histones—proteins that coat DNA and allow genes to be turned on or off.
