Natural selection, which acts on variation, produces results with an extraordinary orderliness. This project seeks to identify and quantify patterns across scales in complex biological and social systems, from the smallest organisms to the largest cities, and to discover the underlying principles and mathematical relationships operating across these seemingly different types of organization.

In biology, comparing species as disparate as mice and whales reveals that much of their physiology and life history follow the same mathematical rules, but at different scales. For example, across mammalian species, metabolic rate -- the amount of energy needed per day to stay alive -- grows by only about 75% with each doubling of body size. Other measurable traits such as life expectancy and heart rate show similarly predictable patterns as species body size increases.

In cities, analogous patterns are observed. With each doubling of city size, almost any socioeconomic statistic that is measureable (wages, patents, and crime rate, for example) increases by about 15% per capita on average. At the same time, the material infrastructural networks that facilitate city life (transportation systems, energy distribution, etc.) decrease in size by about 15% per capita, reflecting economies of scale. These systematic behaviors result from the increasing intensity of human interaction as city size grows.

From politics to economics to culture, our social world ultimately stems from biology, which raises the prospect of finding quantifiable bridges between society and life. One hypothesis this project explores is that networks present in biological systems (the respiratory and circulation systems, for example) and in complex social systems (roads, power lines, social networks) are subject to similar constraints, but are also able to lead to different aggregate outcomes, from larger, slower animals to larger but faster-paced cities.

Such insights lead to further questions. Did human innovations such as language, cities, or culture create a new social dynamic not present in biology? And, looking ahead, how might a better understanding of biological and social regularities lead to further improvements in the human condition?

The Santa Fe Institute thanks the John Templeton Foundation for initiating this work.

Hyejin Youn

Sam Zhang

Yuanzhao Zhang