4A. Growth:

The fact that cities grow is clear. Some of the best observations of growth are provided by satellite images through time like these of Las Vegas and Cairo:

Figure 2: Las Vegas 1973 and 2000

Figure 3: Cairo 1965 and 1998

These are just two cities in a world experiencing explosive urban growth. Cities exhibit a radiating growth pattern strikingly similar to growth patterns observed in fungi:

Some questions of particular interest: which cities are growing? How are they growing (i.e. proportional growth)? For example, Perth, Australia and Philadelphia, USA are growing differently. Perth is a young, booming city, the dominant city of its respective region (Western Australia). Perth has one of the highest proportional growth rates in the developed world. The benefits of regional dominance and how such dominance effects proportional growth becomes clear when we compare Perth with Philadelphia, an older city within a dense mega-city system. A great deal of Philadelphia’s economic and cultural growth/decay is influenced by its recessive role in a crowded system. The image below is testament to the different environments these cities inhabit.


Another feature of growth is a cyclical or wave pattern through which development and economic resurgence occur; cities boom and bust. Waves of urban growth are reminiscent of the rings of growth in trees. Tree rings reflect seasonal growth patterns. Because metropolitan sprawl growth radiates outwards, rings representative of periodic growth can be measured. The size of these rings or magnitude of economic change depends upon the city’s developmental age. Young cities experience high proportional growth while older cities are slow at accommodating technological innovation, thus grow more slowly. In many ways the waves of growth experienced throughout a city’s life can be likened to a set of waves at the beach. A set of waves will progressively build up to the peak wave which will be followed by progressively smaller waves.

While not consciously related to biology, the Russian economist, Nikolai Kondratiev, treated the subject of waves of growth when he proposed the theory that western capitalist economies have long term (50-60 years) cycles of boom followed by depression. These are known as Kondratiev Waves or K-waves. Many economists liken the four distinct stages of a K-wave to the climatic characteristics of the four seasons; winter, spring, summer and fall.

Figure 6: K-waves

There are points of fundamental disagreement among economists about the exact nature of K-waves. Despite this, I included this topic to draw attention to the way economics parallel biology. I am excited that the field of economics can compensate for the subjective shortcomings of biology. Theory, quantitative research and literature in the field of economics offer valuable insight into the biology of cities.