Bob Dylan's Brain Drain

"Ramona, come closer,
Shut softly your watery eyes.
The pangs of your sadness
Shall pass as your senses will rise.
The flowers of the city
Though breathlike, get deathlike at times.
And there's no use in tryin'
T' deal with the dyin',
Though I cannot explain that in lines."
- Bob Dylan, To Ramona from Another Side of Bob Dylan, 1964

"Shadows are falling and I've been here all day
It's too hot to sleep time is running away
Feel like my soul has turned into steel
I've still got the scars that the sun didn't heal
There's not even room enough to be anywhere
It's not dark yet, but it's getting there"
- Bob Dylan, Not Dark Yet from Time Out of Mind, 1997

Is there any difference in quality between these two Bob Dylan lyrics written over 30 years apart?

Closet music historian David Galenson seems to think so:

"The loss of creativity with age suffered by Dylan, [John] Lennon, [Paul] McCartney, and so many of their successors as they have aged is not a phenomenon caused by factors unique to these individuals, or even to rock music. Instead, these artists appear to be prime examples of the loss of conceptual creativity with age, one of the most powerful and pervasive patterns in human creativity."

Galenson is back with a new study looking at the life cycle of songwriters:

The UofC professor compares the life cycles of Golden Era songwriters with those from the 1960's and concludes that -- no surprise -- the Golden Era writers wrote about simpler emotions and tended to become better at their craft with age, peaking in their 30's and 40's. Meanwhile, the artists of the 1960's heralded a new songwriting style which incorporated abstract and conceptual lyrics. These artists tended to peak in their 20's.

Our appreciation of "conspicuous and dramatic innovation" in the arts has risen dramatically and this demand has brought with it a large supply of innovators, Galenson says.

One question: Is this trend speeding up? It seems that with hip hop, the preeminent form of popular musical expression today, artists run out of innovations faster than ever. (Snoop Dogg, Eminem, and Jay-Z are old news.)

UPDATE (10:15 PM)
I'm not completely convinced of Galenson's distinction between conceptual (Dylan) and experimental artists (Golden Era) but in response to some of the comments, here is Galenson's reason for why it's important to investigate these possible distinctions:

"Understanding the conceptual revolution in popular music may therefore do more than heighten our recognition of the importance of Bob Dylan and the Beatles, for it may also help us to appreciate the growing importance of conceptual innovation more generally in our society."

In some senses I think that's very true. Look at the news cycle: Anyone who gets their news from the Internet is not happy to see the same headline on their favorite site for more than an hour or so. That's obviously not conceptual innovation, but it speaks to our continued (and heightened?) desire to have our brains tickled.