I sing.
To a degree, it is natural, in terms of the instrument and aptitude for music.
I have always been able to sing.
However, although I did not have voice lessons, I learned 3 instruments to high level, including a stringed instrument, so I had very good general musical training, and had to develop very good intonation to be able to play the stringed instrument well.
Nobody much outside my family knew I could sing as a child as I was always playing in the orchestra instead. However, I was a chorister at college, so literally sang for my supper. I’ve continued to sing in good and ambitious amateur choirs for the rest of my life.
I believe most people could sing, but confidence is very important, and I think that a lot of people have a negative experience in childhood. I know that some people really cannot, as my own mother is one of them, but they are the exception. I also think that the more you sing, the better you get. The comparative lack of opportunity to sing at primary school compared to when I was young saddens me.