What do the lyrics of Bob Dylan's song "Blowin' in the Wind" mean?

Like many of Bob Dylan's songs (but not so much his topical folk songs of the early 1960s) "Blowin' in the Wind" feature lyrics that are fairly cryptic. At the same time, they are highly suggestive, evoking many of the social issues confronting the United States and the world in the early Sixties. Dylan has been typically evasive in discussing the meaning of the lyrics, mostly reiterating what he said in a 1962 interview:

There ain't much I can say about this song, except the answer is blowin' in the wind. It ain't no book or movie or TV show or discussion group, man. It's in the wind.

That said, let us look at some of the themes Dylan touches on in the song. In the first verse, he is clearly commenting on war. He asks: "How many seas must a white dove sail before she sleeps in the sand?" "Sleeps in the sand" is quite cryptic, and perhaps a bit of poetic license, but clearly the white dove is symbolic of peace. In the next lines he drives the point home by asking: "[H]ow many times must the cannonballs fly before they are forever banned?" In summary, the verse seems to be asking how long it will take until we, as a society, reject war as a means of settling our differences. 

In the second verse, Dylan begins by asking how long a mountain will exist before it is washed into the sea. This imagery suggests something monolithic gradually swept away by the tides of change. This seems to be confirmed by his fairly straightforward evocation of the civil rights struggle in the next lines. Asking how many roads a man must walk down before we call him a man, he then makes the point explicit:

Yes, ’n’ how many years can some people exist
Before they’re allowed to be free?
Yes, ’n’ how many times can a man turn his head
Pretending he just doesn’t see?

Here Dylan seems to be wondering how long it will take to wash away the edifice of racism--for whites to acknowledge the fundamental humanity of African-Americans by affording them equal treatment. Bear in mind that Dylan wrote this song at the height of the civil rights struggle, in 1962. 

In the final verse, he seems to tie together war and poverty, wondering how long we will tolerate injustice in general. "How many ears," he asks, "must one man have before he can hear people cry?" We cannot, he seems to be saying, continue to ignore suffering around us. 

So this song is ultimately about our willingness to confront and overcome the most urgent challenges facing humanity. How long will we continue to accept injustice in the world? "The answer is blowing in the wind." In other words, neither Dylan nor his listeners have the answers, but many of his generation found the questions worth asking in the 1960s.