Wednesday, April 18, 2007

What can Justin Timerblake tell us about evolution?

I read with fascination an article in the New York Times magazine this weekend on Pop Culture entitled "Is Justin Timberlake a Product of Cumulative Advantage?" No, I was not fascinated by the Timerlake part. But what was interesting was Duncan Watt's argument that it is very difficult to predict the success or failure of entities in pop culture. He presented a model that is summarized as "The cumulative advantage:"

The reason is that when people tend to like what other people like, differences in popularity are subject to what is called “cumulative advantage,” or the “rich get richer” effect. This means that if one object happens to be slightly more popular than another at just the right point, it will tend to become more popular still
He then described an experiment they performed that was published in Science last year where
more than 14,000 participants registered at our Web site, Music Lab (, and were asked to listen to, rate and, if they chose, download songs by bands they had never heard of. Some of the participants saw only the names of the songs and bands, while others also saw how many times the songs had been downloaded by previous participants. This second group — in what we called the “social influence” condition — was further split into eight parallel “worlds” such that participants could see the prior downloads of people only in their own world. We didn’t manipulate any of these rankings — all the artists in all the worlds started out identically, with zero downloads — but because the different worlds were kept separate, they subsequently evolved independently of one another.
They used this set up to test among two different possibilities.
First, if people know what they like regardless of what they think other people like, the most successful songs should draw about the same amount of the total market share in both the independent and social-influence conditions — that is, hits shouldn’t be any bigger just because the people downloading them know what other people downloaded. And second, the very same songs — the “best” ones — should become hits in all social-influence worlds. What we found, however, was exactly the opposite. In all the social-influence worlds, the most popular songs were much more popular (and the least popular songs were less popular) than in the independent condition. At the same time, however, the particular songs that became hits were different in different worlds, just as cumulative-advantage theory would predict. Introducing social influence into human decision making, in other words, didn’t just make the hits bigger; it also made them more unpredictable.

Why you may ask am I so fascinated by this? Well, what he described is mathematically and conceptually identical to Luria and Delbruck's fluctuation test (see my earlier blog about L & D), where they were testing the origin of mutants. Luria and Delbruck designed a test where they grew E. coli from the same starting point in different culture tubes. Then they exposed these tubes to selective pressures. If the number of mutants in the tubes were basically the same, this would mean that the mutants arose in response to the selection. If the number of mutants were vastly different (somehting they called a jackpot pattern) this would mean the mutants arose in the growth of the bacteria in the tubes prior to selection.

In the entertainment experiment, the different music "worlds" are the equivalent to the different test tubes. And the preferences of people are the equivalent of the selection. Their result in the music experiment was the jackpot pattern - the same thing seen by Luria and Delbruck. For Luria and Delbruck this meant selection did not guide mutation. For the music, this means the personal preference for the music has less influence than the random history of which music was picked early on.

So - thank you Justin for a modern lesson in evolution.


  1. Ah, ah, not so fast. Just like there's a disputed possibility of adaptive (or "Cairnsian") mutation in violation of Luria-Delbruck, the same goes on in music, and is in fact better supported there.

    You'll find that that the less popular artists don't change their music randomly, but make changes that are specifically adaptive. For example, when Nirvana was popular, all sorts of whiny grunge bands emerged to compete.

  2. Maybe we should write this up - why pop music is like non growing bacteria. We could destroy pop music instantly

  3. Jon, you really should talk to Raissa D'Souza in Mech and Aero Engineering. See this story, "Why the rich get richer." She's interested in networks and how these effects occur. Exactly on point for this work.


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