For all those who think they're not talented and therefore can't learn how to sing, some good news here: Learning to sing is a matter of coordinating and strengthening muscles, so it can be practiced and improved just like anything else. The predisposition is largely the same for everybody (vocal pathologies excluded).
The reason why most people can't just naturally sing well is that singing is not a primary biological function, but a bi-product of a survival mechanism (vocal folds, aka airflow control / airway protection).
The muscles interacting with the vocal folds (thyroarytenoid and cricothyroid) have antagonistic function and work on reflexes rather than control, so the hard part of learning how to sing is to train them to coordinate properly rather than work against each other.