Political demography is the study of the relationship between politics and population change. Population change is driven by classic demographic mechanisms – birth, death, age structure, and migration. Political demography is the study of the relationship between politics and population change. Population change is driven by classic demographic mechanisms – birth, death, age structure, and migration. However, in political demography, there is always scope for assimilation as well as boundary and identity change, which can redraw the boundaries of populations in a way that is not possible with biological populations. Typically, political-demographic projections can account for both demographic factors and transitions caused by social change. A notable leader in the area of sub-state population projection is the World Population Program of the International Institute of Applied Systems Analysis (IIASA) in Laxenburg, Austria. Some of the issues which are studied in the context of political demography are: surges of young people in the developing world, significantly increasing aging in the developed world, and the impact of increasing urbanization. Political demographers study issues like population growth in a political context. A population's growth is impacted by the relative balance of variables like mortality, fertility and immigration. Many of the present world's most powerful nations are aging quickly, largely as a result of major decreases in fertility rates and major increases in life expectancies. As the labor pools in these nations shrink, and spending on the elderly increases, their economies are likely to slow down. By 2050, the workforce in Japan and Russia is predicted to decrease by more than 30 percent, while the German workforce is expected to decline by 25 percent by that year. The governments of these countries have made financial commitments to the elderly in their populations which will consume huge percentages of their national GDP. For example, based on current numbers, more than 25% of the national GDPs of Japan, France and Germany will be consumed by these commitments by 2040. Differential reproductive success is the mechanism through which evolution takes place. For much of human history this occurred through migrations and wars of conquest, with disease and mortality through famine and war affecting the power of empires, tribes and city-states. Differential fertility also played a part, though typically reflected resource availability rather than cultural factors. Though culture has largely usurped this role, some claim that differential demography continues to affect cultural and political evolution. The demographic transition from the late eighteenth century onwards opened up the possibility that significant change could occur within and between political units. Though the writings of Polybius and Cicero in classical times bemoaned the low fertility of the patrician elite as against their more fecund barbarian competitors, differential fertility has probably only recently emerged as a central aspect of political demography.