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GROWTH , INNOVATION , AND THE ACCELERATING PACE OF URBAN LIFE : ARE 21 ST CENTURY CITIES SUSTAINABLE ?
GEOFFREY WEST SANTA FE INSTITUTE
Growth , innovation , scaling , and the pace of life in cities
Luís M . A . Bettencourt * † , José Lobo ‡ , Dirk Helbing § , Christian Kühnert § , and Geoffrey B . West * ¶
* Theoretical Division , MS B284 , Los Alamos National Laboratory , Los Alamos , NM 87545 ; ‡ Global Institute of Sustainability , Arizona State University , P . O . Box 873211 , Tempe , AZ 85287-3211 ; § Institute for Transport and Economics , Dresden University of Technology , Andreas-Schubert-Strasse 23 , D-01062 Dresden , Germany ; and ¶ Santa Fe Institute , 1399 Hyde Park Road , Santa Fe , NM 87501
Edited by Elinor Ostrom , Indiana University , Bloomington , IN , and approved March 6 , 2007 ( received for review November 19 , 2006 )
Humanity has just crossed a major landmark in its history with the majority of people now living in cities . Cities have long been known to be society ’ s predominant engine of innovation and wealth creation , yet they are also its main source of crime , pollution , and disease . The inexorable trend toward urbanization worldwide presents an urgent challenge for developing a predictive , quantitative theory of urban organization and sustainable development . Here we present empirical evidence indicating that the processes relating urbanization to economic development and knowledge creation are very general , being shared by all cities belonging to the same urban system and sustained across different nations and times . Many diverse properties of cities from patent production and personal income to electrical cable length are shown to be power law functions of population size with scaling exponents , � , that fall into distinct universality classes . Quantities reflecting wealth creation and innovation have � �1.2 > 1 ( increasing returns ), whereas those accounting for infrastructure display � �0.8 < 1 ( economies of scale ). We predict that the pace of social life in the city increases with population size , in quantitative agreement with data , and we discuss how cities are similar to , and differ from , biological organisms , for which � < 1 . Finally , we explore possible consequences of these scaling relations by deriving growth equations , which quantify the dramatic difference between growth fueled by innovation versus that driven by economies of scale . This difference suggests that , as population grows , major innovation cycles must be generated at a continually accelerating rate to sustain growth and avoid stagnation or collapse .
population � sustainability � urban studies � increasing returns � economics of scale
umanity has just crossed a major landmark in its history with
Hthe majority of people now living in cities ( 1 , 2 ). The present worldwide trend toward urbanization is intimately related to economic development and to profound changes in social organization , land use , and patterns of human behavior ( 1 , 2 ). The demographic scale of these changes is unprecedented ( 2 , 3 ) and will lead to important but as of yet poorly understood impacts on the global environment . In 2000 , �70 % of the population in developed countries lived in cities compared with �40 % in developing countries . Cities occupied a mere 0.3 % of the total land area but �3 % of arable land . By 2030 , the urban population of developing countries is expected to more than double to �4 billion , with an estimated 3-fold increase in occupancy of land area ( 3 ), whereas in developed countries it may still increase by as much as 20 %. Paralleling this global urban expansion , there is the necessity for a sustainability transition ( 4 – 6 ) toward a stable total human population , together with a rise in living standards and the establishment of long-term balances between human development needs and the planet ’ s environmental limits ( 7 ). Thus , a major challenge worldwide ( 5 , 6 ) is to understand and predict how changes in social organization and dynamics resulting from urbanization will impact the interactions between nature and society ( 8 ).
The increasing concentration of people in cities presents both opportunities and challenges ( 9 ) toward future scenarios of sustainable development . On the one hand , cities make possible economies of scale in infrastructure ( 9 ) and facilitate the optimized delivery of social services , such as education , health care , and efficient governance . Other impacts , however , arise because of human adaptation to urban living ( 9 , 10 – 14 ). They can be direct , resulting from obvious changes in land use ( 3 ) [ e . g ., urban heat island effects ( 15 , 16 ) and increased green house gas emissions ( 17 )] or indirect , following from changes in consumption ( 18 ) and human behavior ( 10 – 14 ), already emphasized in classical work by Simmel and Wirth in urban sociology ( 11 , 12 ) and by Milgram in psychology ( 13 ). An important result of urbanization is also an increased division of labor ( 10 ) and the growth of occupations geared toward innovation and wealth creation ( 19 – 22 ). The features common to this set of impacts are that they are open-ended and involve permanent adaptation , whereas their environmental implications are ambivalent , aggravating stresses on natural environments in some cases and creating the conditions for sustainable solutions in others ( 9 ).
These unfolding complex demographic and social trends make it clear that the quantitative understanding of human social organization and dynamics in cities ( 7 , 9 ) is a major piece of the puzzle toward navigating successfully a transition to sustainability . However , despite much historical evidence ( 19 , 20 ) that cities are the principal engines of innovation and economic growth , a quantitative , predictive theory for understanding their dynamics and organization ( 23 , 24 ) and estimating their future trajectory and stability remains elusive . Significant obstacles toward this goal are the immense diversity of human activity and organization and an enormous range of geographic factors . Nevertheless , there is strong evidence of quantitative regularities in the increases in economic opportunities ( 25 – 29 ), rates of innovation ( 21 , 22 ), and pace of life ( 11 – 14 , 30 ) observed between smaller towns and larger cities .
In this work , we show that the social organization and dynamics relating urbanization to economic development and knowledge creation , among other social activities , are very general and appear as nontrivial quantitative regularities common to all cities , across urban systems . We present an extensive body of empirical evidence showing that important demographic , socioeconomic , and behavioral urban indicators are , on average ,
Author contributions : L . M . A . B ., J . L ., and G . B . W . designed research ; L . M . A . B ., J . L ., D . H ., C . K ., and G . B . W . performed research ; L . M . A . B . and G . B . W . contributed new reagents / analytic tools ; L . M . A . B ., J . L ., D . H ., and C . K . analyzed data ; and L . M . A . B ., J . L ., and G . B . W . wrote the paper .
The authors declare no conflict of interest . This article is a PNAS Direct Submission . Freely available online through the PNAS open access option . Abbreviation : MSA , metropolitan statistical area . † To whom correspondence should be addressed . E-mail : lmbett @ lanl . gov .
This article contains supporting information online at www . pnas . org / cgi / content / full / 0610172104 / DC1 .
© 2007 by The National Academy of Sciences of the USA
SUSTAINABILITY SCIENCE www . pnas . org�cgi�doi�10.1073�pnas . 0610172104 PNAS � April 24 , 2007 � vol . 104 � no . 17 � 7301 – 7306