Self-Destruction of Diversity

Ah, now we start getting to the meat of the economic brilliance of Jane Jacobs.  In chapter 13, she discusses the self-destruction of diversity.  This is a really unconventional way of thinking.  Her argument goes like this: Some districts, by virtue of diversity of compatible uses that bring diverse groups of people at all times of day and night, come alive.  As more and more people come to the district, the rents go up, and as the rents go up, the most profitable uses begin to crowd out those who cannot keep up.  Thus, diversity and liveliness wanes.  Some of the very ingredients that brought about the success of the district eventually brought about its failure.  I have called this process over-success.

Think about Detroit.  It was among the liveliest of cities in 1950 precisely because of the burgeoning success of the automobile industry.  Supporting industries and businesses moved in.  But making cars was extremely profitable, and as more and more space in the city was devoted to automobile manufacturing and supply, everything else began to be crowded out.  The city was given birth to and eventually slayed by the automobile.

If one accepts this argument, it can explain a lot of phenomena that really don’t make a lot of sense otherwise.  The processes and factors of city growth and decline are so mysterious when looked at in the conventional way.  We generally think of growth as coming from the success of one or two large industries, and, similarly, we attribute city decline to the failure of those industries.  But that is not usually what happens in big cities.  Sure, the closing of the steel mills can explain the decline of grey belt cities, but most of them were always small and relatively lacking in diversity.  But when we think about the historical challenges that cities like New York, Boston, and Philly have faced, the downward trends occurred not because of the declining success of the financing and other important industries; they occurred in spite of the growing success of those industries.  Their successes crowded out diversity.

Jacobs connects this phenomenon with the directional problem I wrote about in my previous post.  One would assume that a shift in the center of liveliness in a city is the cause of the old center spontaneously un-diversifying, as if the liveliness is pulled away from it.  But it is much more likely that the over-success of the few high-profit uses pushes the liveliness away from the old center to whatever new place is willing to accept it.

Incidentally, I have been gathering examples of over-success for years and keep running across new ones.  I recently finished a book by Henry Petrosky called “To Engineer is Human,” in which he argues that wild engineering successes teach us nothing and, in fact, often lead to catastrophic failure, because we learn nothing from them. This is classic over-success.  The only way the state of engineering art can be advanced is by learning from failure.  This presents the other side to over-success: under-failure.  When regulations and norms try to prevent failure at all costs, there is often no opportunity to innovate, learn and, eventually, succeed.

What a fantastic world we inhabit where failure can breed success and success can breed failure!