<P> 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 . </P> <P> 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 . This has come about due to medical advances which have lowered infant mortality while conquest migrations have faded as a factor in world history . Differences in immunity levels to infectious diseases between populations also play no major role in our age of modern medicine and widespread exposure to a common disease pool . It is not so much the trajectory of demographic transition that counts as the fact that it has become more intense and uneven in the late twentieth century as it has spread into the developing world . Uneven transitions lend themselves to differential growth rates between contending groups . These changes are, in turn, magnified by democratization, which entrenches majority rule and privileges the power of numbers in politics as never before . Indeed, in many new democracies riven by ethnic and religious conflicts, elections are akin to censuses while groups seek to' win the census' . Ethnic parties struggle to increase their constituencies through pronatalism (' wombfare'), oppose family planning, and contest census and election results . </P> <P> One branch of political demography examines how differences in population growth between nation - states, religions, ethnic groups and civilizations affects the balance of power between these political actors . For instance, Ethiopia is projected to have a larger population than Russia in 2020, and while there were 3.5 Europeans per African in 1900, there will be four Africans for each European in 2050 . Population has always counted for national power to some degree and it is unlikely that these changes will leave the world system unaffected The same dynamic can be witnessed within countries due to differential ethnic population growth . Irish Catholics in Northern Ireland increased their share of the population through higher birthrates and the momentum of a youthful age structure from 35 to nearly 50 percent of the total between 1965 and 2011 . Similar changes, also affected by in - and out - migration, have taken place in, amongst others, the United States (Hispanics), Israel - Palestine (Jews and Arabs), Kosovo (Albanians), Lebanon (Shia, with decline of Christians) and Nagorno - Karabakh (Armenians). In the US, the growth of Hispanics and Asians, and Hispanics' youthful age profile as against whites, has the potential to tilt more states away from the Republican Party . On the other hand, the fertility advantage of conservative over liberal white voters is significant and rising, thus the Republicans are poised to win a larger share of the white vote - especially over the very long run of 50 to 100 years . According to London - based scholar Eric Kaufmann, the high birth rates of religious fundamentalists as against seculars and moderates has contributed to an increase in religious fundamentalism and decrease of moderate religion within religious groups, as in Israel, the US and the Muslim Middle East . Kaufmann, armed with empirical from a number of countries, also posits that this will be further bolstered by the higher retention rates of religious fundamentalists, with individuals in religiously fundamentalist households less likely to become religiously non-observant than others . See also Religious demography § Religious demographics . </P> <P> A second avenue of inquiry considers age structures: be these' youth bulges' or aging populations . Young populations are associated with a ratio of dependents to producers: a high proportion of the population under age 16 puts pressure on resources . A' youth bulge' of those in the 16 - 30 bracket creates a different set of problems . A large population of adolescents entering the labor force and electorate strains at the seams of the economy and polity, which were designed for smaller populations . This creates unemployment and alienation unless new opportunities are created quickly enough - in which case a' demographic dividend' accrues because productive workers outweigh young and elderly dependents . Yet the 16 - 30 age range is associated with risk - taking, especially among males . In general, youth bulges in developing countries are associated with higher unemployment and, as a result, a heightened risk of violence and political instability . For Cincotta and Doces (2011), the transition to more mature age structures is almost a sine qua non for democratization . </P>

What impact might these demographic variations have on the united states politically and culturally