The black swan: not just another imaginary animal

What happens when you run into an imaginary animal, who has been used for centuries as a metaphor?

The black swan living near Pont Neuf since at least January 2012 when this lovely video http://www.youtube.com/watch?v=MQHXTZO1798 was posted by Andylamen.
My photo of the black swan living near Pont Neuf in Toulouse in September 2013.

I’m fond of metaphors (isn’t everybody?) and I’m particularly fond of imaginary creatures. On a cloudy Sunday I ran into…

a black swan.  This black swan. No, it isn’t Nessie! Really! If you don’t believe me look at the great video posted by Andylamen in January 2012.

Black swans have been used as a metaphor since Roman times through the present.

How come? 

Because they’re very rare. To be precise, there aren’t any. In the northern hemisphere.

Since it was common knowledge that all swans are white, the Roman poet (~55-~138CE) Juvenal used the black swan as the ultimate rare bird in his Sixth Satire:

rara avis in terris nigroque simillima cygno (6:165)

Which translates to

a rare bird in these lands, much like a black swan

For now I’ll ignore the fact that he was referring to “a perfect wife.”   The Sixth Satire is a diatribe against Roman women, and more generally against marriage. It tells us quite a bit about Roman gender roles of the time. More about versions of perfect wives another day.

Juvenal coined several other expressions that are still used today, such as panem et circenses and mens sana in corpore sano.

In much of Europe, black swans were a metaphor of something that didn’t exist. You know, an imaginary creature.

Oops, black swans do exist…

In 1697 the Dutch explorer Willem de Vlamingh discovered black swans  in Australia, where they are very common. There are also white swans in Australia, but they’re less common. (Interestingly, of the seven species of swans, the two species from the southern hemisphere have black plumage over all or part of their bodies.)

The assumed non-existence of black swans and their subsequent discovery made them an excellent example to think about what can be verified.

What is a scientific statement?

According to philosopher of science Karl Popper (1902-1944), a scientific statement is one that can be falsified. Not verified, but falsified.

Because verification and falsification are asymmetric.

“All swans are white” can be falsified, by finding a black swan.

No matter how many white swans we find, we can’t be sure we’ve seen them all. However, as soon as we find one black swan, the statement has been falsified.

Time for another metaphor: black swan events

More recently Nassim Taleb used black swans as a metaphor in his work on uncertainty (Fooled by Randomness, The Black Swan, Antifragile) .

A black swan is an event that:

  1. is an outlier, far beyond past experience or expectations
  2. has huge impact
  3. is subsequently explained as predictable

Black swans can be positive (like the invention of the internet) or negative (the 9/11 attacks or the Fukushima disaster). Taleb notes that most positive black swans make themselves known gradually — especially compared to the suddenness of negative ones.

As a former earth scientist, I wonder at the relationship between black swans and extreme events, such as intense storms or prolonged drought. Extreme events are very unlikely but have huge impact.

Taleb’s whole point is that normal statistical distributions don’t apply in the realms he discusses, which are human and societal or in the interaction of natural and societal.

Height and wealth

An example he uses is the difference between the distribution of height and of wealth.

Heights follow standard distributions, which he refers to Mediocristan. A valid prediction is possible with partial information in Mediocristan.

But in Extremistan, the few very very large values overwhelm the distribution. The net worth of the very very very rich (the infamous 1% of the Occupy movement) dominate estimates of total wealth.

Our need for cause and effect narratives

I’m particularly intrigued by the post hoc claims of predictability. This goes directly to the common adage of “hindsight is 20/20 vision.” In a nutshell, after something happens, it’s easy to build a causal narrative which conveniently leaves out anything that isn’t consistent with what actually occurred.

The desire for causality is inherent to human nature. It’s why we crave fiction, be it films or novels or television. E. M. Forster’s famous definition of plot versus story alludes directly to causality and the search for meaning.

The king died and then the queen died,’ is a story. ‘The king died, and then the queen died of grief’ is a plot.   Aspects of the Novel (1927)

It’s not quite the same as encountering a unicorn, but by running into a black swan, I was given an excuse to find out more about an (non) imaginary creature and why it’s become a metaphor for thinkers for over 2000 years.

Have you ever run into an imaginary creature? What happened?

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