Cities and marketplaces are central to economic development, but we know little about the mechanisms that cause such agglomerations to form. I theorize that evolutionary forces select for agglomerations when individuals desire to spatially coordinate exchange in complex environments. To test this idea, I perform a laboratory experiment where geographically dispersed individuals bring different goods to a location for trade. Consistent with the theory, I find that individuals spontaneously coalesce to reap the gains from exchange and there is more agglomeration in economies with a larger variety of goods. I also find that agglomerations re-emerge at the same locations after shocks, being land-tied reduces agglomeration but magnifies the effect of variety, individual location choices aggregate to create a Zipf population distribution, and individuals earn more in agglomerations.

城市和市场是经济发展的核心，但我们对导致这种聚集形成的机制知之甚少。我的理论是，当个体希望在复杂环境中进行空间协调交换时，进化力量会选择聚集。为了验证这个想法，我进行了一项实验室实验，其中地理上分散的个人将不同的商品带到一个地点进行交易。与该理论一致，我发现个人自发地联合起来从交换中获得收益，并且在拥有更多种类商品的经济体中存在更多的集聚。我还发现集聚在冲击后重新出现在相同的位置，与土地绑定减少了集聚但放大了多样性的影响，个体位置选择聚合以创建齐夫人口分布，