Some people can’t make out melodies at all. But others enjoy music, understand relative pitch, but just can’t quite tell the difference between “vocally close to on key” and “really on key”. It’s apparently a much more subtle problem than I realized, especially since these folks can make out the pattern of tones in human speech perfectly fine. (One of those neural things that shows how song is processed differently than speech, in the brain.) However, even if this is a genetic problem, it raises the possibility that someday some kind of therapeutic brain workaround can be figured out, possibly through the linguistic brain connections that are working on all cylinders. Maybe not essential for life, but still it would be nice for people.
(Real tone deafness — as opposed to people who are casually called “tone deaf” because they don’t know how to make their voice match pitches or have a physical throat disability, but who can clearly make out the difference between what their voices are doing and what they should be doing. People who just have problems controlling their vocal apparatus can often learn how to sing well; they just need a lot of patience and determination. Some voice teachers and speech therapists are very good at helping such people.)
She has some definite ideas about the cruelty of those first few episodes of the reality talent search shows, where they usually find some poor person to make fun of.
A lot of people wonder why some people try out, why they think they’re good, and why their families encourage them and think they’re good singers if they’re clearly not. (As opposed to nervous people singing badly once, or people with bad song or stylistic choices.) The secret may be this: tone deafness is not only genetic, but runs in families. 39% of the first-degree relatives of tone deaf people are tone deaf themselves. So these shows really are preying on the innocently ignorant, in many cases.
A Science Daily article on amusia (a-musi-a, that is). Lots of interesting related stories are linked there.