"Not sure what you mean by 'physically wrong with them'. "
Maybe 'physically' is the wrong word Mike.
The vast majority of people, from the earliest age, are able to learn to copy singing and to make notes relate to one another to make them into a tune.
I don't understand 'tone deafness' but thought it was a physical problem (might be wrong about that)
I have been told it occurs in a small number of people, but quite often it has been claimed by people without any evidence - an excuse, if you like.
We had several singers in our workshop who claimed 'tone-deafness' without exception, they left singing.
Anybody who thinks they have a real problem should sek advice before they diagnose themselves.
Jim Carroll