In 1907 Cecil Sharp observed that the transmission of folk songs and the forms they took when they were collected and attested was the result of three factors: continuity, variation, and selection. These factors were expanded on in 1954 by the International Folk Music Council, which wrote that:

    Folk music is the product of a musical tradition that has been evolved through the process of oral transmission. The factors that shape the tradition are: (i) continuity which links the present with the past; (ii) variation which springs from the creative impulse of the individual or the group; and (iii) selection by the community, which determines the form or forms in which the music survives.

    The term can be applied to music that has been evolved from rudimentary beginnings by a community uninfluenced by popular and art music and it can likewise be applied to music which has originated with an individual composer and has subsequently been absorbed into the unwritten living tradition of a community.

    The term does not cover composed popular music that has been taken over ready-made by a community and remains unchanged, for it is the re-fashioning the re-creation of the music by the community that gives it its folk-character.

One immediate problem I have here is evolved through the process of oral transmission For the last century at least it would probably more correct to substitute aural for oral. If this is true then variation which springs from the creative impulse of the individual or the group becomes a deliberate reinvention. I would suspect the more accurate interpretation may be that words are misheard and the tune is slightly mistaken as the song travels from one person to another. Today when a mobile phone can capture both sound and vision flawlessly how can such evolution of a song/tune occur unless deliberate? This would take away a degree of spontaneity that is sort of implicit in the traditional view of song evolution and make it a deliberate cold blooded massacre of the original.
The 1954 definition takes no account of the impact of modern technology on it's perception of the folk process.