Hope really does matter, as outlined in a recent paper (pdf) by Treb Allen of Northwestern, with the formal title “The Promise of Freedom”:

This paper examines the extent to which the fertility of enslaved women was affected by the promise of freedom. Because women derived greater pleasure from children when they were free, increases in the distance to freedom (which lowered the probability of escape) should reduce fertility. Exploiting the Fugitive Slave Law of 1850 and the particularity of U.S. geography, I demonstrate a strong negative correlation between fertility and the distance to freedom. This negative correlation is stronger on larger plantations, but disappears when the father of the child is white. The correlation varies with the difficulty of the route, and a similar correlation is not present for white children or for slave children born prior to the Fugitive Slave Law. The negative correlation suggests that despite the small number of successful escapes, the promise of freedom played an important role in the everyday lives of slaves.

There are more interesting papers by Allen here., including on the gravity equation and location theory. Allen is one of the most interesting young economists today, yet he remains undercovered. Here is Treb on “Equilibrium distribution of population if the surface of the world was shaped like a cow.”