Population, Ideas, and Economic Growth

本提案中概述的研究项目是由两个经验事实驱动的：在过去的125年里，美国人均收入增长率缺乏任何明确的趋势；在过去100万年的历史中，世界人口增长率在加速，从平均仅略高于零的速度到目前每年约2%的速度。第一个事实是Kaldor（1961）表达的观点的基础，并体现在许多增长模型中，即平衡、稳定的增长是我们的模型应该匹配的关键事实。第二种观点恰恰相反：至少在世界历史的大部分时间里，人口增长——大概还有人均收入增长——一点也不稳定。本建议的第一个项目将提出一种经济增长的一般理论，其中人均收入增长和人口增长是紧密联系在一起的。正如最近的许多论文所述，经济增长是因为知识储备的增长。然而，该理论进一步指出，知识存量的增长是由于人的增长，而人是思想的发明者。内生的人口增长和由思想的非竞争而产生的规模回报的增加被视为内生增长理论的两个关键组成部分。第二个项目考察了这一基本理论在多大程度上可以定量地解释激发提案的两个事实。最近的几位作者，如Klenow和Rodriguez-Clare（1997）以及McGrattan和Schmitz（1998）指出，令人惊讶的是，很少有研究新增长理论模型的定量含义并试图区分这些模型的工作；这个项目就是朝这个方向迈出的一步。第一个应用程序将使用新的增长理论框架对20世纪美国的增长进行增长核算。初步结果表明，美国近期经济增长中只有约1/4与长期因素（世界人口增长）有关；剩下的3/4似乎是模仿平衡增长路径外观的暂时性因素的结果。第二种应用将把土地添加到内生生育率/观念框架中，并认为Kremer（1993）检验的人口证据可以理解为一条漫长的过渡路径。最后，第三个项目将研究新思想的生产函数的形状，这在新增长理论中起着关键作用。对这个生产函数的初步探索强化了平衡增长不太可能发生的观点。这一提议的结果对许多增长理论中的隐含假设提出了质疑，即我们的模型应该永远产生持续、平衡的增长，这在一定程度上是由卡尔多程式化的事实所驱动的。

The research projects outlined in this proposal are motivated by two empirical facts: the lack of any clear trend in U.S. per capita income growth rates during the last 125 years and the acceleration of world population growth rates throughout a million years of history, from rates averaging only slightly more than zero to the present rates of around two percent per year. The first fact underlies the view expressed by Kaldor (1961) and embodied in many growth models that balanced, steady-state growth is a key fact our models should match. The second suggests the opposite: at least for the bulk of world history, population growth-and presumably per capita income growth as well-is anything but steady.The first project in this proposal will suggest a general theory of economic growth in which per capita income growth and population growth are tightly linked. As in many recent papers, economies grow because of growth in the stock of knowledge. However, the theory goes further to suggest that the stock of knowledge grows because of growth in the stock of people, the inventors of ideas. Endogenous population growth and the increasing returns to scale that results from the nonrivalry of ideas are viewed as the two key ingredients of a theory of endogenous growth.The second project examines the extent to which this basic theory can explain quantitatively the two facts that motivate the proposal. Several recent authors such as Klenow and Rodriguez-Clare (1997) and McGrattan and Schmitz (1998) note that there is surprisingly little work designed to examine the quantitative implications of the models of new growth theory and to attempt to distinguish among these models; this project is a step in this direction. The first application will conduct a growth accounting exercise for 20th century U.S. growth using a new growth theory framework. Preliminary results suggest that only about 1/4 of recent U.S. growth is associated with the long-run component (world population growth); the remaining 3/4 seems to be the result of transitory factors that mimic the appearance of a balanced growth path. The second application will add land to the endogenous fertility/ideas framework and argue that the population evidence examined by Kremer (1993) can be understood as one long transition path.Finally, the third project will examine the shape of the production function for new ideas, which plays a key role in new growth theory. Preliminary exploration of this production function reinforces the notion that balanced growth is unlikely to occur.The results from this proposal raise questions about the implicit assumption in much of growth theory, motivated partly by the Kaldor stylized facts, that our models should generate sustained, balanced growth forever.