本文研究了蛛网模型中的聚合动态，其中学习通过选择机制发生，通过该机制，更成功的企业以更高的速率复制。该模型的结构允许分析地描述总体动态，并计算选择性的替代水平对福利的影响。一个核心方面是，更大的选择性虽然使企业类型的分布更接近于给定日期的最优分布，但往往会使经济在总体水平上不那么稳定。正如Nelson和Winter(1982)的研究，企业在劳动力/资本比率上存在差异。他们并不是最优的选择，而是企业的一个特征。随着时间的推移，公司的分布会朝着有利于最赚钱的公司类型的方向发展。选择可能是不充分的，因为公司是根据不正确的市场信号选择的。选择本身可能会强化这种错误定价，从而产生不稳定性。我比较了在生产率冲击的波动性和持久性以及劳动力供应弹性方面存在差异的经济体。主要发现如下。 First, a trade-off arises since greater selection allows to better track shocks and limits mutational drift in firm types; on the other hand, selection may strengthen cobweb oscillatory dynamics. Second, there seems to be a value in maintaining a diverse "ecology of firms", in order to cope with future shocks. These observations explain the key results. Optimal selectivity is larger, the less "cobweb unstable" the economy, i.e. the more elastic the labor supply. Second, optimal selectivity is larger, the more persistent the aggregate productivity shocks. Finally, optimal selectivity is larger, the lower the variance of productivity innovations. The model can be extended to allow for firm entry and trend productivity growth, and a selection process with memory. Empirical evidence suggests that, in accordance to the model, countries with less regulated product markets exhibit lower aggregate inertia.