Who is Saint Jeffrey in the Catholic religion? In columns 1 and 2 the dependent variable is the share of Muslims in 1900 across countries from McCleary and Barro (2005), while in columns 3 and 4 the dependent variable is the share of Muslims across ethnic groups from the World Religion Database (WRD). The empirical analysis is conducted across countries and across ethnic groups within countries. To explore this prediction, in Columns 3 and 4 of Table 3B, we focus on ethnic groups outside Muslim empires, further distinguishing between regions that were already monotheistic by 1050 CE as classified by O’Brien (1999). Column 3 shows that limiting the sample to polytheistic areas during the diffusion of Islam, distance to trade routes is more precisely estimated. We discuss the various mechanisms that may give rise to this phenomenon and offer evidence consistent with the view of Islam as an institutional package appropriate for societies residing along unequally endowed regions in the vicinity of trade opportunities. This view of Islam as an institutional package engineered to allow the flourishing of long-distance trade across unequally endowed regions generates an auxiliary prediction: Islam should be able to gain a hearing more readily across unequal territories close to trade routes.

Considering that monotheism was an attractive ideology compared to polytheism, regions outside the Muslim empires where monotheism was already present should be less receptive to the spread of Islam along trade routes. Second, we establish that Muslim communities tend to reside in habitats that are ecologically similar to those of the Arabian Peninsula, the birthplace of Islam. For example, focusing on specific regions where historical data may be available, one may explore time variation in the speed at which Islam made inroads to the respective communities. Although the decline in the predictive power of inequality in agricultural endowments farther from trade routes is consistent with the proposed view that Islamic rules were better suited for geographically unequal communities close to the trade network, it is far from a proof. We view this finding as offering large-scale econometric support to a widely held conjecture among prominent Islamicists like Lapidus (2002), Berkey (2003), and Lewis (1993), and complement this empirical regularity with historical accounts illustrating the importance of trade contacts in the process of Islamization of various prominent locations in Africa and Asia. Observations are at the level of ethnic group, the sample is the Old World (Europe, Asia and Africa).

Specifically, in Appendix Table 4 we show that Muslim societies as recorded by ethnographers in the Old World are more likely to be politically centralized, harbor beliefs in moral gods, and follow equitable inheritance rules. We linked Murdock’s Ethnographic Atlas groups to the Ethnologue’s linguistic homelands in the Old World. Groups residing in homelands of limited potential for agriculture dotted with few pockets of fertile land also used to obtain more from herding and less from agricultural products in the pre-colonial era. 2008) and provide at the grid level of 0.083 by 0.083 decimal degrees estimates on the share of land allocated to pasture and agriculture in 2000. We aggregate this information at the homeland level to obtain a measure of how tilted land allocation is towards pasture. In the first three columns of Table 6, the dependent variable is the log ratio of pastoral over agricultural area in 2000 across linguistic homelands.16 All columns include country-specific constants. Overall, the results in Table 6 reveal how the specific geographic endowments of Muslim homelands give rise to a distinct specialization pattern: a pastoral economy with few farmers where trade is important. Overall, a poor and unequal distribution of agricultural potential predicts Muslim adherence.

These findings highlight the, until now, neglected crucial role of trade in shaping the differential adherence to Islam across ethnic groups and shed new light on the geographical origins and spatial distribution of Muslims within modern-day countries. Columns 3 and 6 of Appendix Table 3 clearly show that Muslim representation both across countries and across-groups within countries has a concave relationship with proximity to trade. Across both levels of aggregation, there is a robust link between proximity to pre-Islamic trade routes, geographic inequality, and Muslim representation. Historically, Australia largely tried to prevent immigrants from China and throughout Asia from settling there. Australia is the largest country in the area of Oceania. In this environment where each area specializes in its comparative advantage (farmers on the fertile pockets and herders on the relatively arid ones), a larger geographical Gini coefficient may correspond to larger potential gains from trade. First, it may be that those persons who do not believe are, for one reason or another, not ready to believe that God exists, perhaps because of emotional or psychological or other reasons. What arguments may then rationalize the voluntary adoption of Islam across geographically unequal regions? Then apply hairspray liberally to keep all that hair in place!