The Ant and the Grasshopper: Seasonality and the Invention of Agriculture
Review and Resubmit at Quarterly Journal of Economics

During the Neolithic Revolution, seven populations independently invented agriculture. In this paper, I argue that this innovation was a response to a large increase in climatic seasonality. Hunter-gatherers in the most affected regions became sedentary in order to store food and smooth their consumption. I present a model capturing the key incentives for adopting agriculture, and I test the resulting predictions against a global panel dataset of climate conditions and Neolithic adoption dates. I find that invention and adoption were both systematically more likely in places with higher seasonality. The findings of this paper imply that seasonality patterns 10,000 years ago were amongst the major determinants of the present day global distribution of crop productivities, ethnic groups, cultural traditions, and political institutions.

All Along the Watchtower: Linear Defenses and the Introduction of Serfdom in Russia 

Why did Russia enserf its previously free peasants, just as Western Europe was undergoing the opposite transition? Domar argued that Russia’s low population density would have resulted in a high equilibrium wage, and therefore created the incentives for the nobility to restrict labor mobility, so as to appropriate the agricultural surplus. However, while this explains the cross-sectional pattern, it cannot explain why serfdom was not reintroduced in the west after the Black Death. In this paper I propose a new theory, that argues that serfdom was necessary to ensure that the defense cordon against the Tatar slave raids from the south could be effectively manned. In support of my the- ory I demonstrate a geographic association between serfdom and the sequence of linear defenses employed. I also deploy spatial methods to calculate the optimal invasion routes for Tatars, as well as the optimal defense lines to block the raids. I find that modern patterns of development are significantly correlated with calculated defense lines towards the South, where nomadic raids made the cordon defense necessary, but not towards the West, where invaders had extensive logistical tails and could be effectively parried by blocking only the major roads. 

What Have the Romans Ever Done for Us? Aqueduct Suitability and the Administration of Empire

The ancient Romans built over a thousand aqueducts throughout the Empire, supplying  water for private, agricultural, and manufacturing use. To what extent did the engineering superiority of the Romans promote peaceful relations with their subjects? Provinces with many aqueducts were usually under civilian administration, while provinces with fewer aqueducts were generally administered by the commander of the local legion. To limit the possibility of reverse causality between efficient capital investments and sentiment towards the occupiers, I use cross-sectional variation in rainfall and the availability of  natural springs to construct a measure for the usefulness of Roman hydraulic technology. I find that provinces with a greater fraction of dry land within 30km of a suitable spring had more aqueducts, and were also more likely to be under civilian administration.