Sarah Perry, October 2014





Abstract

European cultures have historically prevented people from restricting family size within marriage. The European marriage pattern allowed for the control of fertility only through delaying and restricting nuptiality. A new pattern, allowing for controlled fertility within marriage, simultaneously originated in New England and France in the late eighteenth century. The new pattern traveled with a new set of values, including suffrage, democracy, equality, women’s rights, and social mobility. Its main mechanism of spread was education, the availability of which also incentivized the new fertility pattern’s adoption by providing a clear way for parents to compete for the future status of their children by having fewer children. The new pattern spread across Europe, North America, and Australia during the late nineteenth and early twentieth century, encountering temporary, partial resistance from some groups. Even Catholics and Mormons worldwide adopted controlled fertility by the early twentieth century or earlier. As the new pattern grew to dominate the western world in the twentieth century, Asia and Latin America transitioned to the new pattern. Sub-Saharan Africa entered a fertility transition beginning in the 1980s that is ongoing. In each of these transitions, when controlled fertility was adopted, the pre-transition positive (eugenic) relationship between fertility and wealth became a negative (dysgenic) relationship. Only tiny pockets of culture that maintain extreme separation from the new pattern – especially through refusing outside education and preventing women from contact with the outside world – have fertility patterns plausibly consistent with uncontrolled fertility. These may include the Amish and Hassidim in the United States. Once the fertility transition to controlled fertility occurs in a population, its fertility generally continues to decline until it is below replacement. The benefits of the new pattern are increased material wealth per person, a reduction in disease, starvation, and genocide, and upward social mobility. The main drawback is the onset of a dysgenic phase that may end civilization as we know it.



Introduction to Cultural Evolution

By creating language, humans opened up a new frontier for evolution. Cultures – a group’s collection of language, beliefs, behaviors, rituals, music, stories, rules, taboos, and markers of status – are made of information, transmitted from generation to generation and group to group. Cultures, or memeplexes, influence the genetic success of their adherents, often acting heterogeneously on members of their constituent populations. They form a major part of the selective environment itself, shaping the size and composition of the groups of humans they rely on to reproduce themselves.

memeplex: the collection of values, beliefs, practices, rituals, music, art, rules, stories, and markers of status that makes up a human culture, is passed from generation to generation within a population, and is sometimes passed from one population to another.

Although cultural evolution operates by very different mechanisms than genetic evolution, many biological patterns are present. Cultures mutate, reproducing varying versions of themselves by generational transmission and spread, experience differential reproductive success (selection), and sometimes go extinct. They are dependent on their human hosts, or symbiotes, a population they both change and are changed by. And we are dependent on them.

There are two ways that memeplexes can reproduce themselves: first, they can reproduce intergenerationally, being passed on to the genetic descendants of their adherents. Second, they can reproduce by spread or diffusion, transmitted from their adherents to people other than their own genetic descendants, such as to neighboring groups. In early human groups, cultures were mostly limited to the first method of reproduction. However, advances in technology, such as the invention of writing and, later, of printing, increased the importance of the second method of cultural transmission. This change relaxed selection on memeplexes in a crucial way: their success became less dependent on the genetic fitness of their adherents.



A Cultural Evolution History of Fertility

Where cultures may only be transmitted to the genetic descendants of their people, fertility norms are perhaps the most important aspect of cultural evolution. Every human group ever studied by anthropologists has a population policy (Murdock, 1945); while usually not explicit, every culture has norms and behaviors that limit population or mandate its increase. Different environments and technological packages are associated with different fertility norms. Arctic hunter populations face different pressures than medieval European farmers, and different fertility norms are successful in maintaining or even increasing a stable memeplex-reproducing population.

Matras (1965) identified four possible fertility strategies that a human culture might include:

A early marriage, uncontrolled fertility

B late marriage, uncontrolled fertility

C early marriage, controlled fertility

D late marriage, controlled fertility

Controlled fertility is not an artifact of modernity. Hunter-gatherers often control their fertility within marriage, whether by infanticide or by non-reproductive sexual practices or abstinence. The number of children born to the average hunter-gatherer woman ranges from .87 to 8.5, and in many groups is less than three (Marlowe, 1965). The higher values are consistent with uncontrolled (natural) fertility (Bongaarts 1978), but the lower numbers indicate some form of fertility control. (Differences in nuptiality do not explain the variance.)

Hunter-gatherer populations varied substantially in population policy, depending on the demands of their environment and mode of subsistence. As some groups began to practice agriculture, however, they faced the opportunity to dramatically increase their populations and take over new lands populated by hunter-gatherers by achieving high population densities. Territory determined the success of farming cultures, and a high population was crucial to maintaining and even expanding territory. Memeplexes whose population policy mandated uncontrolled fertility now had a major advantage against those that didn’t. When an agricultural culture is expanding into a frontier populated only by hunter-gatherers, whether in the Stone Age or in the eighteenth century, only cultures establishing early, universal marriage and uncontrolled fertility as the norm are successful. Populations either increased and expanded or were kept in check by mortality.

Early marriage and uncontrolled fertility were probably the norm in all of Europe prior to the sixteenth century. This pattern exists today in sub-Saharan Africa and Afghanistan, and in isolated pockets elsewhere, though this has often been the result of a fertility transition away from an earlier, controlled norm. Improvements in agricultural productivity have mimicked the selective effects of a frontier, relaxing the need for cultural limitation of fertility, much as that experienced by the Stone Age European farmers and colonial American farmers.

Around the sixteenth century, Europeans west of the Hajnal line began to switch to a pattern of late marriage, with a significant proportion of people never marrying, and uncontrolled fertility within the population who married. This norm was likely not adopted for the conscious purpose of limiting the population, but had the effect of keeping the population somewhat more comfortable below the Malthusian limit (Clark 2009). In preindustrial Japan and parts of China, however, farmers in long-settled areas kept early and universal marriage, but adopted fertility control by selective female infanticide and other means. In these populations, almost all women married and married young, but had around three children during their lives (Jones 1990 at p. 118). With industrialization and agricultural advances offering a pseudo-frontier relaxing Malthusian limits, the Japanese briefly adopted uncontrolled (or at least much less controlled) fertility, but after World War II they began to control their fertility once more. Most existing populations have been through multiple fertility transitions, and each transition has shaped the population.

Almost the entire world has recently undergone a single fertility transformation, one from uncontrolled fertility to controlled fertility. This transformation began in the late eighteenth century in a few small villages in France and New England, and subsequently spread to every continent and almost every population in the world. Europe at this time exhibited both early and late marriage patterns, but uncontrolled fertility was the norm, a crucial part of a memeplex maintained by the Catholic Church and other institutions at the center of every community.

What caused this worldwide fertility transition? Why did it start where and when it did, and what were the mechanisms of its spread? Why did so many humans adopt fertility norms at odds with their own genetic fitness? And what made some societies immune? What follows is a theory for the timing, location, spread, and limits of the modern fertility transition, taking into account the cultural, economic, and reproductive histories of dozens of populations. In short, it is a battle of the memeplexes.



A Note on the Non-Role of Child Mortality in the Fertility Transition

Since child mortality has drastically declined in the last century, many assume that child mortality had a role in people’s decisions to limit fertility. This is a problematic conception: child mortality can only affect fertility when parents have a “target” parity in mind; in uncontrolled fertility regimes, no such target exists, so there is no sense in which parents might “replace” deceased children to achieve their target. The transition is from an uncontrolled fertility regime to a controlled regime; this “target parity” is the very essence of the transition that must be explained.

Indeed, in sample after sample, decreasing mortality is found to have no role in decreasing fertility; it occurs at the wrong time and in the wrong place to be causal (see, e.g., Guinane 2010, Murphy 2012, Cummins 2012).



The Uncontrolled Fertility Norm in the Catholic Memeplex

In the centuries leading up to the eighteenth, European cultures, whether marrying early or late, exhibited uncontrolled fertility. Fertility outside of marriage was prevented and punished, but there was a positive obligation to realize one’s natural fertility if married. The enforcement of this obligation was centralized in the Catholic Church, which played a role in its communicants’ lives so extensive it is hard for moderns to imagine it.

The uncontrolled fertility norm was crucial to the success of the memeplex stewarded by the Catholic Church, by the mechanism described in an earlier section. The fact that it is a positive obligation implies that it has costs to individuals, who might benefit from “defecting.” Defecting, in this sense, means not maximizing one’s fertility within marriage. If humans directly wished to maximize their own fertility, such a positive obligation would not be necessary. But, as is often said, humans are adaptation executors, not fitness maximizers. Human preferences often align with high fertility, but high fertility is not itself the target. Sexual images of young, fertile women are desirable even though they do not increase fertility; similarly, sugar is not disdained simply because it is no longer scarce enough to promote health. One of the strongest drives that humans exhibit is for high social status. In all human societies prior to the recent global fertility transition, status was strongly correlated with fertility. Like sugar and sexual images, humans continue to seek status for its own sake even when it ceases to be correlated with fertility.

People compete for status along many dimensions. In order to sustain high fertility in its host population, a memeplex must effectively forbid competition along one particular axis: competing for status (one’s own or that of one’s children) by reducing the number of births. In many situations, it may be tempting for people to “defect” from a high-fertility norm by having fewer children, in order to have a less burdensome life themselves, or in order to improve the health and social status of their smaller number of children. This latter is what modern demographers call the “quality-quantity tradeoff;” it is a tradeoff that is forbidden by uncontrolled fertility norms. Luckily for memeplexes with this norm, there were few opportunities for upward mobility in social status in the world before the eighteenth century. Social and religious pressure was enough to prevent most would-be “defectors” from realizing these marginal opportunities; those that tried risked outcast status, and one’s fertility was highly observable by the community.

How was the Church able to impose this norm on people who had incentives to defect by controlling fertility? The Church derived its power from its deep involvement in its members’ lives. It was able to offer a profound spiritual gift: contact with the Divine as part of a community. In the fifth century, worship in Christian churches on Sundays was not just a single service, but an “interlocking series of services” beginning before dawn and continuing until after dusk (Kavanagh 1984, at pp. 56-60). Everyone participated in at least some of the services, including laudes at dawn, processions across the city, lively preaching, communion, and vespers at night; only the most pious participated in all of them. In medieval Europe, the Church had dominion over time itself, from the calendar of holidays organizing the sacred year to the church bells declaring the hours. It provided musical and other refined aesthetic experiences at a time when they were scarce, elaborating its own holiness and meaning. It united Christians under a loving, powerful, and soon-returning God.

With the invention of the printing press in Europe in the fifteenth century, a new memetic frontier opened. Over the following centuries, literacy expanded dramatically; people were able to access a new universe of cultural items, including new ideas and old books (especially the Bible) that were previously only accessible to the elite few. The earliest Protestants encouraged people to read the Bible for themselves, instead of accessing the divine only through community worship and rites guided by priests. The Catholic Church was no longer able to maintain memetic control over religion; heretical sects with mutant ideologies caused havoc (see, e.g., Carlin 2013). The Catholic Church itself entered a more literary phase as well, calcifying the “primary theology” discovered through community contact with the divine into “secondary theology” refined and approved by experts in ivory towers (Kavanagh 1984). People’s need for contact with the divine through rite was not being met by the calcified liturgy of the Church as it existed after the Council of Trent, not to mention the English Act of Uniformity of 1549 (Kavanagh 1984, at p. 81). The intimate contact with the divine offered through reading the Bible for oneself (or with one’s own charismatic preacher) proved tempting for the spiritually undernourished. Literacy, and the Church’s response to it, weakened the Church’s control over its members even as powerful new memeplexes were being born to compete with it. One of these new memeplexes would come to dominate the entire world.



The New Memeplex

In a few ordinary villages in New England and a few ordinary villages in France, commencing around the year 1776, a new memeplex was being created. Those who adopted it began to control their fertility within marriage. On two different continents and in two different languages, small communities had adopted new sacred virtues, competing with the sacredness of the old memeplex. The new sacred beliefs included democracy and suffrage, equality, universal education, and the rights of women. In America, temperance and abolition were gradually added, and as the memeplex gained power, it began to emphasize centralized organization. Like many religions, its claims to universal truth made it imperative for its adherents to impose it even upon unwilling participants in distant lands.

The memeplex that precipitated low fertility was not industrialization. The fertility transition occurred in rural as well as urban areas. More importantly, the fertility transition was centered on France, whereas the industrial revolution spread outward from England. Genetic and linguistic distance from France predicted the spread of the fertility transition within Europe between 1830 and 1970, supporting a model of cultural adoption of new norms and behaviors at the memetic “frontier” (Spolaore et al. 2014) rather than economic responses to industrialization. The same pattern of cultural transmission can be observed within the United States.

The new memeplex offered adherents the opportunity to compete along the long-forbidden dimension: by limiting their fertility. The revolutionary atmosphere in the late eighteenth century promised upward social mobility, and for the first time, there were major gains available to one’s children’s future status from trading off child “quantity” for child “quality.” An educated child, it now seemed, might rise above his parents’ station in life, a station previously accepted without question for centuries. By the nineteenth century in New England, members of the religious arms of the new memeplex controlled their fertility in order to have fewer children of better “spiritual quality,” a thought unthinkable in Catholic terms (Parkerson et al. 1988). “Pietism emphasized direct contact with God by personal prayer and scripture reading, and the need to inclucate this spirituality in young children,” say Parkerson et al. “It fostered a sense of individualism and self-worth, and put women in leadership roles that permitted notions of gender equality to emerge.”

These American religions stewarding the new memeplex were cultural descendants of the Puritan religions, formed and reformed in Great Awakenings, new memetic entities promoting new sacred beliefs often in conflict with the old ones. They allowed adherents previously forbidden gains in status in exchange for limiting fertility; and as more people began to compete along this dimension, those who did not were at a disadvantage.

It should be noted that the quality-quantity tradeoff here is not for better evolutionary quality. For example, in a large Swedish sample over many generations, children from smaller (limited) families had more education and achieved higher socioeconomic status, but had fewer children themselves (Goodman et al. 2012). Status was passed on at the expense of evolutionary fitness. There is no mystery here. Status has been reliably associated with high fertility for so long that humans pursue it for themselves and their children for its own sake, just as they enjoy sugar for its own sake.

Parents had been asked, it seemed, for centuries to come to a miniature version of the Repugnant Conclusion. Under the new pattern, a parent was able to form a sort of alliance with his first few children, increasing their well-being at the (unfelt) expense of the existence of their never-born siblings. When the birth of children was firmly the responsibility of God, this calculation was not even considered. But imagine an eighteenth century peasant watching his neighbor’s few, well-fed children gain status through education, while his own, many children are malnourished with no prospects beyond his own. Combined with the waning influence of the Church’s memetic package, the direct observation of Fortune’s smile must have been compelling. Only those in very tightly-knit religious communities, exercising a high degree of social control, and ideally rarely observing small families in practice, were immune. Only they were not compelled to compete by fertility control – at least, for a limited time, and in a progressively limited manner.



The Role of Women’s Rights

The new memeplex that drove the fertility transition to controlled fertility replaced the old sacred values of hereditary hierarchy, religious obedience, and traditional gender roles with new values, including equality, democracy, education, women’s rights, upward mobility, and suffrage. Education seems to be the primary means of transmitting the memplex and incentivizing the adoption of the new fertility pattern. However, the other factors are also important in transmitting the low-fertility pattern, though their importance varies over time. Women’s status does not seem to have been a very important determinant of the early fertility decline, though it has clearly been a determinant of the most recent fertility transition to sub-replacement fertility.

It is difficult to quantify women’s rights or women’s status in order to measure their effect on fertility. However, the late eighteenth century and early nineteenth century do not seem to have been periods in which women enjoyed particularly high status, even in New England and France. Women in the United States did not gain suffrage until the early twentieth century; prior to the mid-twentieth century, women who attempted to compete with men were regarded as objects of ridicule. Rousseau, whose writings likely originate with (and partly make up) the new memeplex, prescribes a traditional role for women, taking care of children and attending to the home sphere, distinct from the role of men. While female literacy predicted lower fertility during the early transitions, these women were a long way from liberated, and the low fertility pattern was able to spread in countries in which women had very low status at the time, such as Japan.

In addition, the means that were used to space births during the early fertility transition – namely, periodic abstinence and withdrawal – would have required the participation of men. Workforce participation for women was extremely low at the beginning of the nineteenth century, around 5%, and rose very slowly during the nineteenth century. By most definitions, in the United States, traditional gender roles survived into the 1950s, when the fertility transition was already long over. While women’s rights and status would become important determinants of fertility in the twentieth century, education and social mobility seem to be more important fertility determinants in the initial transition to controlled fertility.

During the later fertility declines, women’s rights were very important as women themselves were incentivized to compete for status via education and careers. The pattern of voluntary childlessness is relatively new outside monastic contexts. It is not merely a tail of the desire for smaller families, as rates of having zero children frequently decreased as families got smaller; voluntary childlessness bears no consistent relationship to fertility (Gobbi 2011). Only later, as new, nonreproductive roles for women emerged, did voluntary childlessness begin to become common. Women’s education is also important in fertility transitions of developing countries, in which it is highly correlated to the use of modern contraceptives (Ainsworth et al. 1995). When women are taught to understand and trust the new Western memeplex, they are more willing to limit fertility using its medical technology, which might otherwise be scary and forbidden. In developing countries in which contraceptive use is not universal, female education is a strong predictor of the use of contraception (Bbaale et al. 2011, Gribble et al. 2008).



1776 at Ground Zero of the Fertility Transition

In order for the new memeplex to make progress against the old memeplex, several conditions had to be met:

The weakening of the institutions of the old memeplex A new set of sacred beliefs that could compete with the old sacred beliefs Economic and social conditions that rewarded competition on future children’s status by restricting one’s own fertility Institutional mechanisms for the spread of the new memeplex

As we have seen, the influence of the Catholic Church and its organization and control of communities had been substantially weakened during the Enlightenment. The American Revolution and French Revolution were products of a new set of sacred beliefs, valuing democracy, equality, suffrage, and education. The equality and social mobility made possible by the Revolutions increased the returns possible from status climbing, which was rarely possible before. Democratic reforms were associated with increasing public spending on education; education was at once an important mechanism by which people could trade off fertility for future child status, and a mechanism for the spread of the ideas of the new memeplex. Only those who maintained church control, rejected the new education, and prevented competition with the outside world were able to slow the spread of the new memeplex’s fertility pattern – for a while.

The fertility transition began at the same time at two places where conditions were particularly hospitable to the new form of future-oriented status competition. In both New England and France, the fertility transition began not in the wealthiest areas, but in more modest areas with low inequality. New England was both less wealthy and more equal than the South (Lindert et al., 2012), and within the South, high wealth and high inequality negatively predicted the spread of education (the most crucial component of the new memeplex) within counties (Ager 2013). Within France, those villages (Cummins 2013) and county-equivalent départements (Murphy 2012) that were the first to switch to the new fertility regime were poorer and more equal than similar areas that did not experience a fertility decline. Villages that experience fertility decline were more equal (measured by gini coefficient) than England or non-decline villages, and wealth as measured in wills was less correlated with father’s wealth in fertility decline villages, indicating higher social mobility (Cummins 2009). “Decreases in the level of economic inequality, associated with the 1789 Revolution, suggest that the environment for social mobility changed to incentivize lower fertility in France,” says Cummins (2013). The social and economic changes surrounding the American Revolution likely had the same effect, as ideals of universal education, equality, and suffrage found adherents in New England as well.

However, within these modest French villages, it was the wealthier members who limited their fertility first. Within Cummins’ (2013) “decline villages” – those experiencing the fertility transition – the wealthiest tercile of families reduced their fertility the most. In “non-decline” villages, where fertility remained high, the wealthy had more children. These two fertility regimes map directly to the two memeplexes that are battling. Below, from Cummins (2013), shows the relationship between fertility and wealth at the individual level under the two regimes between 1750 and 1810:

In the New England town of Hampton, New Hampshire, it was the middle tercile of families who reduced their fertility the most (Kilbourne 1986). Ambitious middle-class families from modest areas had the most to gain in social mobility from limiting their fertility and educating their children. They were the first to undergo the fertility transition, but others soon followed their example. By the time the fertility transition was detectable at the state level in New York in the nineteenth century, it was the wealthiest families who limited fertility the most (Haines 2008). When England experienced its fertility decline in the late nineteenth century, it was the poorest members of the highest social class (professionals) who reduced their marital fertility first (Cummins 2009) – apparently hoping to avoid downward social mobility rather than provide for the upward social mobility for their children. This pattern represents a clear departure from the eugenic, Malthusian European regime of the past, during which those with the highest wealth and status experienced the highest fertility.



The Role of Education

The new memeplex was both incentivized and spread by education (Perry 2014a and Perry 2014b). Education was costly, both in terms of expenses and in terms of forfeiting children’s labor, but returns to education in terms of both status and income were beginning to be positive for a large number of people in eighteenth century France and New England. Prior to the eighteenth century, only elites had access to education; but in the period leading up to the Revolutions, universal education gradually became a sacred mandate. Connecticut and the Massachusetts Bay Colony mandated universal elementary schooling in the 1640s and 50s, says Kenny (2008). Major educational reforms were carried out in New Hampshire as early as the seventeenth century (Wallace), and education was a major Revolutionary priority in late-eighteenth-century France (Markham).

In transitioning France, education of children (as well as mother’s literacy) was correlated with decreasing fertility (Murphy 2012). Within the United States at the same time, years of education was highly predictive of fertility decline, while income bore no consistent relationship (Hansen et al., 2014).

Spatially, the fertility transition in the United States began in New England in the late eighteenth century, then spread from the northeastern coastal states across the North to the West, and finally to the South. The map below shows the woman-child ratio (a proxy for fertility) at the county level in the United States in 1800: (from Haines et al. 2011)

In 1800, the fertility transition was underway in modest rural villages in two coastal areas, centered on Cape Cod and the Chesapeake Bay. By 1840, the low-fertility pattern centered on Cape Cod had intensified and spread to the west in the North, but not in the South (Haines et al., 2011):

At this point, education had been widely adopted in the North, and significantly less in the South. The following map (my own) illustrates the spatial distribution of education at the state level in 1840. The metric is the state’s number of children attending primary and grammar schools and academies, but not colleges, as a proportion of the number of white children ages 5-14 in the state, calculated from the 1840 census. As with fertility, education spread west in the North, but not in the South.

In the map above, enrollments approached the ideal of universal education in the Northeast, northern midwestern states made some progress, and the South educated only a small fraction of its youth. Between 1840 and 1880, fertility dropped substantially more in the Northeast than anywhere else, and fell least in the South (Hacker 2009).

In the years that followed, enrollment rates would increase rapidly in the northern Midwest, but would stagnate or even decrease in much of the South. The following map (Bleakley et al. 2013) shows the change in enrollment rates in counties across the United States between 1850 and 1870:

The states in the Northeast were already educating almost all their children in 1850, and their enrollment rates did not change much. Across the northern Midwest, enrollment rates soared, but stagnated or decreased across much of the South. Note that the figure only takes white enrollment rates into consideration, so the difference between Northern and Southern states is not just measuring the percentage of recently freed slaves.

By 1860, using white child-woman ratios as a proxy for fertility, lower fertility appears to have spread into parts of the south (Haines et al. 2011):

Within the South, the inverse relationship between fertility and education remained strong (Bleakley et al. 2009):

Hookworm, an intestinal parasite that primarily affects children and causes lethargy and anemia, but not mortality, was endemic to many parts of the South until the early 20th century. A major eradication effort was launched in 1910, and was extremely successful. Bleakley et al. (2009) posit that hookworm acted as a barrier to education, effectively increasing the cost of educating children. In areas with high infection rates, education and literacy increased and fertility declined when the parasite was eradicated. Areas with lower infection rates experienced less education increase and less fertility decline. By 1920, much of the South appears to have adopted the controlled fertility norm, and educational improvements would only increase from that point on.

Across the United States, as immigrant and native populations were exposed to the new memeplex advocating upward mobility, education, and equality, more and more Americans switched to a controlled fertility pattern. The education rate for blacks lagged that of whites until the early 20th century (Margo 1990); accordingly, black fertility began declining much later than white fertility, but then fell faster than white fertility (Haines et al. 2006, Table 1). Uncontrolled fertility groups (such as Irish immigrants in the early twentieth century) that encounter the strong, fully-formed memeplex when it is already widely accepted tend to experience rapid drops in fertility compared to the initial slow decline of the innovators; American blacks may have been culturally removed enough from the status competition domain of whites to exhibit a similar pattern.

The fertility-education relationship is also present in Europe during the fertility transition. For example, this map depicts the relationship between fertility and education in Prussia in 1849, when the fertility transition was well underway (Becker 2009):

This pattern is exhibited virtually everywhere the fertility transformation takes place, from Iran (Raftery et al. 1995) to Nepal (Axinn 2001). During Nepal’s transition, just being near a school reduced a woman’s fertility even if neither she nor her children attended it. The more the new memeplex gained in worldwide power and status, the more powerful it became at bringing new converts under its spell. Education has spread much more quickly in the recent era than during the first decades of the fertility transition (Benavot et al. 1988).

As noted above, the early converts in Europe were those with close genetic and linguistic distance from France (Spolaore 2014). In South America between 1870 and 1940, states with populations predominantly of European origin were most likely to expand education (Benavot et al. 1988). Among Europeans, the population most susceptible to the early forms of the new memeplex, education is associated with democracy and suffrage. In both France during the Revolution and Britain a century later, major public educational provisions were enacted shortly after a major expansion of suffrage (Kenny 2008). In France, the enactments occurred during the Revolution, and French marital fertility fell below 10% of its previous level for the first time in 1827. So many people had switched away from uncontrolled fertility that the phenomenon was now visible at a country level. In Great Britain, the education enactments occurred in 1870 and 1891, and Great Britain’s fertility first fell 10% below its prior level in 1892 (Spolaore 2014).



Hold-Out Groups

Return for a moment the map of 1800, 1840, and 1860 fertility above (the black-and-white maps by Haines et al. 2011). Notice the high fertility area at the northern tip of Maine. This area was heavily Catholic, as seen in this map of Catholic Churches per county in 1860 (Mullen 2013):

For decades, it formed one of the “hold-out areas” that maintained high fertility despite dropping fertility all around. In the next section, we will examine these hold-out groups and find out what caused them to resist the new fertility norms, the mechanisms by which they did so, and how the nature of the norm changed over time.



The Changing Nature of High Fertility: Catholics and Mormons

Catholics and Mormons in the United States maintained higher fertility than other religious groups, and the Irish, Spanish, and Dutch maintained high fertility for a long time after the fertility transition in Europe. However, all these groups have subsequently adopted the modern controlled fertility pattern, and their adoption of controlled fertility within marriage appears quite early. Instead of maintaining the old, uncontrolled fertility pattern, Catholics and Mormons appear to have shifted to controlled fertility, but at a higher target parity (or lower target spacing) than the surrounding population. In both cases, the nature of church control changed: it was not able to mandate true uncontrolled fertility, but was able to convince parents not to stray too far from the community mean on the highly observable metrics of birth spacing and parity. During the latter half of the twentieth century, the fertility of Mormons and Catholics descended well below any possible natural fertility population, converging at or just above the non-Mormon, non-Catholic mean. These institutions have been fighting losing battles against the new controlled fertility pattern, defending ever-shrinking concessions to higher fertility.

The role of theology in maintaining high fertility is secondary to the role of community control (Goldsheider 2006). The religious community can exercise indirect control by preventing contact with extra-religious status seeking, such as through providing religious rather than public education and emphasis on traditional gender roles; and it can exercise direct control through surveillance of birth spacing and parity by religious officials and by the community. By maintaining control of primary education, by being the center of social life among its communicants, and by surveilling the birth spacing of its members, the Church slowed but did not ultimately prevent the adoption of controlled fertility. Instead, the Church maintained a high target parity (or low target birth spacing) among its members even as they controlled their fertility. This target parity decreased over time; this is consistent with Catholics and Mormons controlling fertility and targeting the current mean parity or birth interval (so as to avoid detection by being average), as the mean would decrease over time by this process alone.

The Mormon fertility transition occurred over the latter half of the nineteenth century, just after the frontier peak in fertility (Heaton 1998). Mormon women born in 1840-1845 had on average around nine children, and the maximum parity observed was a staggering 22 (Bean 1990 at pp. 186-202). Mormon women born in 1895-1899, however, had an average of around five children, with the maximum observed birth order being just ten. Age at marriage declined only one year during that time, and the period of lactational infecundability remained constant. Beginning with the 1860-1865 cohort, women were clearly utilizing fertility control by birth spacing, and their fertility control started earlier and became more effective over time. By 1900, the Utah LDS were no longer a natural fertility population, but a controlled fertility population with a high target parity (ibid).

During the twentieth century, LDS birth rates ran parallel to but higher than the American birth rate (Heaton 1998).

Throughout the twentieth century, samples of Mormon college students and families have reported high rates of usage of fertility control, as well as high rates of usage (Bush 1976). The LDS fertility rate is presently probably about three children per woman, much higher than the average white American fertility rate, which is below two. Again, while the LDS Church was not able to maintain a genuinely uncontrolled fertility pattern, despite narratively compelling pronatalist theology and strong community involvement, it has maintained a target parity somewhat above the background level.

This is not the case for modern Catholic populations. In the United States, Catholic and Protestant fertility converged in the 1970s, and both are currently below replacement (Frejka et al. 2006). Catholic fertility in Southern Europe has also fallen to below replacement since the 1970s (Berman et al. 2007). But throughout the nineteenth and twentieth centuries, Catholic communities maintained high fertility for long periods of time even as the fertility transition accelerated in surrounding populations.

French Canadians arrived in Canada in the seventeenth and eighteenth centuries, from home populations practicing the late marriage, uncontrolled fertility European marriage pattern. While the French who stayed in France experienced a fertility decline, shifting to controlled fertility, the French Canadians experienced a fertility transition in the opposite direction – to early marriage and uncontrolled fertility (Milot et al. 2011). Fertility rose significantly, consistent with the frontier pattern, as each generation of women was able to give birth slightly earlier than the last. While the rest of Canada transitioned to controlled fertility early and quickly, French Canada transitioned very slowly; births per woman declined 23% between 1851 and 1921 in Quebec, compared to a 51% decline for Anglophone Canadians during the same time period (Krull et al. 2003, note 1). French Canada likely ceased to be a natural fertility population during this time period. During the 1960s, during a period of modernization and change, total fertility in Quebec suddenly decreased by half, to below the replacement rate, where it remains today (Krull et al. 2003). Thus, in cooperation with linguistic and cultural isolation, the Catholic Church in French Canada was able to slow the fertility transition and maintain a high target parity until the 1960s.

A similar pattern appears in Ireland, with both the initial slow decline and the final rapid decline occurring later than the decline in French Canada. Controlled fertility is first apparent from census data in the first decade of the twentieth century in Ireland (David et al. 1995). In 1911, 14% of completed Irish families had more than ten children; by 1946, only 5% of Irish Catholics had more than ten children, and only 3% had more than ten in 1961 (Kennedy 1973 at p. 185). The proportion having 7-9 children decreased from 36% in 1911 to 16% in 1961, and smaller family sizes became proportionally more common.

The Catholic Church in Ireland was able to maintain natural fertility until 1900 and a high (though decreasing) target parity thereafter. The Catholic Church controlled the school system in Ireland, ensuring that children were not indoctrinated in “new memeplex” ideas. Interestingly, when free public education was mandated in Ireland in 1892, primary school enrollments rose from 50.7% in 1890 to over 80% in 1900 (Benavot et al. 1988). This may or may not be related to the onset of fertility control shortly thereafter. Fertility rose again around 1929, when birth control was criminalized in Ireland, another demonstration of the strength of the Catholic Church. Finally, in the early 1980s, Irish fertility declined to approximately the replacement rate, and hovers around the replacement rate today.

Irish immigrants to the United States did not demonstrate the same fertility pattern as the Irish who remained in Ireland. Irish-Americans had higher fertility than native-born Americans, but lower than those who remained in Ireland (Guinane et al. 2004). They became a controlled fertility population almost immediately upon arrival, but maintained a high target parity, though this declined with successive generations. Irish Catholic immigrants who moved to areas with low Catholic populations, on the other hand, experienced approximately normal American fertility levels. The Catholic Church was able to maintain some control in America, but only within tightly-knit Catholic communities, and only to a lesser degree than the Catholic Church in Ireland. As noted above, American Catholic fertility has since fallen below replacement. In 1965, when American Catholic fertility rates were beginning to converge with non-Catholic fertility rates, 4.4 million children attended Catholic elementary schools out of a Catholic population of around 46 million. This number steadily declined even as the Catholic population increased; in 2014, only 1.3 million children attend Catholic elementary school out of a Catholic population of around 66 million. As the influence of the Catholic Church declined, Catholic fertility declined as well.

The Netherlands is another predominantly Catholic country that displayed high fertility relatively late for Europe. Dutch Catholics were likely a natural fertility population until the late nineteenth century, while liberal Dutch protestants had higher birth intervals indicative of deliberate birth spacing (Van Bavel et al. 2004). Van Bavel et al. are too quick to attribute the early fertility decline to breastfeeding; it is possible to estimate the interval of lactational infecundity (as in Bean 1990) and measure its variation over time, but this is not done here. At any rate, all religious groups’ fertility declined slowly but relentlessly between marriages in 1885 and marriages in 1955 (Somers et al. 2003):

Catholic fertility was initially highest but declined the most, from almost 9 children per woman in 1885 to just over three in 1955. Liberal protestant births and “no religion” births had already declined to this level by 1925. Whenever the onset of controlled fertility, the Catholic Church successfully maintained a higher target parity than other religions until the 1940s, when traditional Calvinists first exceeded Catholic fertility. As in the United States, a fundamentalist protestant community maintained higher fertility than the general population for a time; unlike the Mormons in the United States, however, the fertility of the Calvinists, like all groups in the Netherlands, continued to decline, converging at between 2 and 2.5 births per woman in the 1990s. The fertility rate in the Netherlands has since fallen to below replacement.



Fertility in the World Today

Since the inception of the fertility transition in the late eighteenth century, every country in the world has transitioned to controlled fertility (Bongaarts 2013). Europe and North American transitioned first, with European populations around the world leading the way, as in South America (Schultz 2005). East Asia transitioned next, and accomplished its transition fastest. Latin America, South Asia, and West Asia followed, and sub-Saharan Africa transitioned last and slowest. It is still in the process of transitioning today, and fertility rates remain the highest in the world (Schultz 2005):

Fertility in the developing world has declined from 6.1 children per woman in 1960-1965 to 2.7 children per woman in 2005-2010 (Bongaarts 2013), with fertility falling slowest in the poorest parts of the world. Fertility in sub-Saharan Africa has fallen only 19% over this period of time, but it has entered the controlled fertility revolution. Fertility in the developed world is much lower and commonly below replacement.

In each country from the eighteenth century until today, a very important transformation takes place as fertility begins to be controlled. In uncontrolled fertility regimes, wealth (and income, and education) are positively correlated to fertility; as the transition occurs, these become negative predictors of fertility, though not necessarily at the same time. Finland is the only country in which the husband’s income correlates positively to fertility (Weiss 2008). Other countries, from Europe to sub-Saharan Africa, exhibit a pattern in which the intelligent, careful, and wealthy limit their fertility earlier and more than the dull, profligate, and poor (from Gribble et al. 2008):

The uncontrolled fertility pattern is a thing of the past outside of small groups that renounce non-religious education and involvement with the outside world. While some Amish orders appear to be natural fertility populations, there is some evidence of fertility control by birth spacing in Amish populations (Greksa 2002). Little evidence is available for Hassidic and Haredi Jewish populations, but the sociologist Bruce Phillips (in unpublished research) has been cited as saying that Hassidic birth rates average 7.9 births per women, within the range of natural fertility populations. The true test of a natural fertility population is the existence of extremely high parity families, and there do appear to be Hassidic families numbering fifteen children. Haredi rates are lower, 6.6 per woman, perhaps indicative of fertility control. Some modern Hassidim do use birth control (personal correspondence), and it is possible that these populations will transition to the modern fertility pattern.



Effects of the Fertility Transition

The modern low-fertility pattern has allowed humans to spread the fruits of economic development among fewer people, resulting in a standard of living that pre-1800 populations never dreamed of. Starvation, disease, and genocide, the dangers of high population density, have been averted on a massive scale. It is difficult to imagine the misery that would have accompanied industrialization without controlled fertility.

However, the new fertility pattern has changed the population of humans, as memeplexes do. The old fertility pattern, in which the wealthy had more surviving children, increased the genetic share of the population that was intelligent and careful (Clark 2009). The new fertility pattern, in which education and wealth negatively predict fertility, both within and between populations, means an ever-smaller genetic share of the population is intelligent and displays low time preference. It is a form of selection, just as deadly pathogens killing those without genetic resistance to them is a form of selection. Intelligence is highly heritable in humans (Davies et al. 2011), as is time preference (Carpenter 2011). The Flynn Effect has masked the genetic effects of the new selection environment (Weiss 2008), and the new memeplex itself had come to regard talk of good people husbandry as a sacredness violation. At any rate, it is too late to address the changes caused by the new fertility pattern on a global scale (Weiss 2008).



Conclusion

The traditional fertility pattern in Europe, from Roman times until the eighteenth century, was uncontrolled fertility, in which those who married had as many children as they were biologically capable of having. Some European populations transitioned to a pattern of late and non-universal marriage, which reduced fertility, but couples did not control their fertility within marriage. In the late eighteenth century, in New England and France, a new pattern emerged, in which married couples controlled their fertility within marriage by spacing their births. This pattern was associated with a new memeplex, which promoted democracy, suffrage, education, women’s rights, and equality. The spread of the new fertility pattern was distinct from the spread of industry in the Industrial Revolution; rather than being centered on England, it was centered on less-industrialized France and New England, spreading first to culturally similar populations through education and religion. For the first time, parents competed for the status of their future children by reducing their family size. The Catholic Church, and to a lesser extent other churches, resisted the new fertility pattern, but all populations eventually adopted it. An important characteristic of the transition is that in post-transition societies, the poor and uneducated have more children, whereas in pre-transition societies, the wealthier and more educated have more children. At present, most European populations have transitioned to sub-replacement fertility patterns; even Mormons in Utah exhibit only three births per woman. Those countries and populations whose fertility transitions occurred later retain much higher fertility. These patterns have left their imprint on the genetic composition of the population of the world, perhaps the most important form of human selection of our time.



Appendix: Deliberate Fertility Control among England’s Elite in 1800?

Cummins (2009, Chapter 4, co-written with Gregory Clark) presents a theory that the wealthiest members of English society intentionally decreased their fertility around 1800, much earlier than the fertility decline in England, which occurred about 90 years later. Further, he proposes that the mechanism of fertility decline was “stopping” behavior, ceasing fertility at a target parity, rather than increasing the birth interval or “spacing.” While Cummins’ dissertation presents invaluable information about the relationship between fertility and status in transitioning France and England, there are reasons to be skeptical of this particular claim.

Cummins & Clark present strong evidence of a total fertility decline among the wealthiest segment of English society beginning around 1800, data extracted from thousands of recorded wills executed in England. While elite fertility was higher than the fertility of the poor before 1800, after 1800 it was lower. However, the evidence is much weaker that this elite fertility decline was a result of controlled fertility. Instead, it appears to be an exaggerated form of the Western European marriage pattern. Indeed, age at marriage for elite women rose by about two years during the period of the fertility decline. Cummins & Clark say that this higher age at marriage cannot explain the entire fertility decrease, but this conclusion seems unwarranted.

Evidence for deliberate fertility control comes from a much smaller sample of only a few hundred wills. There is no evidence of an increase in the birth interval for the wealthy during this period, so spacing – the mechanism underlying every early fertility decline discussed thus far – is ruled out as a candidate. Instead, Cummins et al. posit that couples decreased their fertility by stopping at a target parity, a pattern not seen in any other early fertility decline. This conclusion rests on very slim evidence.

The chart above (Cummins 2009) depicts the birth interval and the interval between marriage and the final birth for the four wealth groups, group 1 being poorest and group 4 being richest. Before the fertility decline in 1800, the interval between marriage and the last birth for poor women was 9.5 years; for the richest women, it was 13.2 years. However, after 1800, the poorest women maintained their same marriage-last birth interval at 9.5 years, but the richest women reduced their marriage-last birth interval to 10.5 years, a reduction of 2.7 years. Given the small sample sizes, this appears easily within the range of marriage-last birth intervals for women practicing uncontrolled fertility but marrying two years later. It does not seem parsimonious to posit highly anomalous (not to mention technologically precocious) “stopping behavior” when the interval between the alleged “stopping” and the natural course of menopause appears to be about .7 years.

From the same small sample, Cummins and Clark tabulate the age at final birth for women of the four classes:

All classes of women decreased their age at last birth within this sample, not just the elite group Cummins et al. claim practiced precocious stopping. Only the reduction in age at last birth for the second-wealthiest group is significant in this sample, which does not fit with the story of elite stopping, and is just as likely noise. For the highest-wealth elite group (group 4) after 1800, age at last birth (35.2) is higher than the age at last birth in all other post-1800 groups. This is difficult to harmonize with a picture of falling elite fertility from stopping behavior. The poor are not hypothesized to have controlled their fertility, yet they cease reproduction around age 32 or 33; but the elite are suspected of stopping after a final birth at the age of 35.

There is also the fact that, unlike other early fertility transitions, this one did not spread. These anomalies and evidence problems should make us skeptical of any deliberate within-marriage fertility control among the English elite in the early eighteenth century.

Ager, Philipp. “The Persistence of de Facto Power: Elites and Economic Development in the US South, 1840-1960“. No 38, Working Papers from European Historical Economics Society (EHES), 2013.

Ainsworth, Martha, Kathleen Beegle, and Andrew Nyamete. “The impact of female schooling on fertility and contraceptive use : a study of fourteen sub-Saharan countries. World Bank Living Standards Measurement Study 110, February 1995.

Axinn, William, and Jennifer Barber. “Mass Education and Fertility Transition.” American Sociological Review 66:481-505, August 2001.

Bbaale, Edward, and Paul Mpuga. “Female Education, Contraceptive Use, and Fertility: Evidence from Uganda. Consilience: The Journal of Sustainable Development 6 :1:20–47, 2011.

Bean, Lee, Geraldine Mineau, and Douglas Anderton. Fertility Change on the American Frontier: Adaptation and Innovation. Berkeley: University of California Press, 1990.

Becker, Sascha, Francesco Cinnirella, and Ludger Woessmann. “The Trade-off between Fertility and Education: Evidence from before the Demographic Transition.” IZA Discussion Paper No. 4557, November 2009.

Benavot, Aaron, and Phyllis Riddle. “The Expansion of Primary Education, 1870-1940: Trends and Issues.” Sociology of Education 61:3:191-210, July 1988.

Berman, Eli, Laurence Iannaccone, and Giuseppe Ragusa. “From Empty Pews to Empty Cradles: Fertility Decline Among European Catholics.” National Bureau of Economics Research Working Paper Series 18350, May 2007.

Bleakley, Hoyt, and Fabian Lange. “Chronic Disease Burden and the Interaction of Education, Fertility, and Growth.” The Review of Economics and Statistics 91:1:52-65 , February 2009.

Bleakley, Hoyt, and Sok Chul Hong. “When the Race between Education and Technology Goes Backwards: Post-bellum Decline of White School Attendance in Southern US.” Unpublished manuscript, The University of Chicago, April 2013.

Bongaarts, John. “A Framework for Analyzing the Proximate Determinants of Fertility.” Population and Development Review 4:1:105-132, March 1978.

Bongaarts, John. “How Exceptional is the Pattern of Fertility Decline in Sub-Saharan Africa?. United Nations Population Division, Expert Paper 2013/4, 2013.

Bush, Lester Jr. “Birth Control Among the Mormons: Introduction to an Insistent Question.” Dialogue 10:12-44, 1976.

Carlin, Dan. Hardcore History #48: Prophets of Doom (podcast). April 2013.

Carpenter, Jeffrey, Justin Garcia, and J. Koji Lum. “Dopamine receptor genes predict risk preferences, time preferences, and related economic choices.” Journal of Risk Uncertain 42:233–261, 2011.

Clark, Gregory. A Farewell to Alms. Princeton University Press, 2009.

Cummins, Neil. “Why Did Fertility Decline? An Analysis of the Individual Level Economic Correlates of the Nineteenth Century Fertility Transition in England and France.” Doctoral Thesis, London School of Economics and Political Science, 2009.

Cummins, Neil. “Marital fertility and wealth during the fertility transition: rural France, 1750–1850“. The Economic History Review 66:2:449–476, May 2013.

David, Paul, and Warren Sanderson. “Cohort Parity Analysis and Fertility Transition Dynamics: Reconstructing Historical Trends in Fertility Control from a Single Census.” Population Studies 44:421-445, 1990.

Davies, G., A. Tenesa, A. Payton, J. Yang, S. Harris, D. Liewald, X. Ke, S. Le Hellard, A. Christoforou, M. Luciano, K. McGhee, L. Lopez, A. J. Gow, J. Corley, P. Redmond, H. C. Fox, P. Haggarty, L. J. Whalley, G. McNeill, M. E. Goddard, T. Espeseth, A. J. Lundervold, I. Reinvang, A. Pickles, V. M. Steen, W. Ollier, D. J. Porteous, M. Horan, J. M. Starr, N. Pendleton, P. M. Visscher and I. J. Deary. “Genome-wide association studies establish that human intelligence is highly heritable and polygenic.” Molecular Psychiatry 16:996-1005, October 2011.

Frejka, Tomas, and Charles Westoff. “Religion, Religiousness and Fertility in the U.S. and in Europe.” MPIDR Working Paper WP 2006-013, May 2006.

Gobbi, Paula “A Model of Voluntary Childlessness.” Working Paper 2011-1, IRES, Université catholique de Louvain, January 2011.

Goldsheider, Calvin. “Religion, Family, and Fertility: What Do We Know Historically and Comparatively?” in Religion and the Decline of Fertility in the Western World, F. W. A. van Poppel and Renzo Derosas (eds.), Springer, 2006.

Goodman, A., Koupil, I., and Lawson, D.W. ““. Proceedings Biological sciences / The Royal Society, 279:1746:4342-51, 2012.

Greksa, L. “Population growth and fertility patterns in an Old Order Amish settlement.” Annals of Human Biology 2:29:192-201, 2002.

Gribble, James, and Joan Haffey. “Reproductive Health in Sub-Saharan Africa.” Population Reference Bureau, 2008.

Guinane, Timothy. “The Historical Fertility Transition: A Guide for Economists.” Center Discussion Paper 990, Economic Growth Center, Yale University, October 2010.

Guinane, Timothy, Carolyn Moehling, and Cormac Grada. “The Fertility of the Irish in the United States in 1910” Economic Growth Center Discussion Paper 848, January 2004.

Hacker, J. David. “New Perspectives on the Fertility Transition in the United States, 1850-1880.” Presented at the IUSSP International Population Conference; Marrakesh, October 2009.

Hacker, J. David, Libra Hilde, and James Holland Jones. “The Effect of the Civil War on Southern Marriage Patterns.” Journal of Southern History 761:39-70 , February 2010.

Haines, Michael, and Avery Guest. “Fertility in New York State in the Pre–Civil War Era.” Demography 45:2:345-361, May 2009.

Haines, Michael, and J. David Hacker. “Spatial Aspects of the American Fertility Transition in the Nineteenth Century, in Navigating Time and Space in Population Studies 37, M.P. Gutmann et al. (eds.), International Studies in Population 9, 2011.

Haines, Michael, and David Hacker. “The Puzzle of the Antebellum Fertility Decline in the United States: New Evidence and Reconsideration.” NBER Working Paper No. 12571, October 2006.

Hansen, Casper Worm, Peter Jensen, and Lars Lonstrup. “The Fertility Transition in the US: Income or Schooling?.” Social Science Research Network, January 2014.

Heaton, Tim. “Vital Statistics,” in Latter-day Saint Social Life: Social Research on the LDS Church and its Members, Provo, UT: Religious Studies Center, Brigham Young University, 1998.

Jones, Huw Roland. Population Geography. New York: Guilford press, 1990.

Kavanagh, Aidan. On Liturgical Theology. New York: Pueblo Publishing Company, 1984.

Kennedy, Robert E. The Irish: Emigration, Marriage, and Fertility. Berkeley: University of California Press, 1973.

Kenny, Charles. “The Global Expansion of Primary Education“, 2008.

Kilbourne, Lawrence J. “The Fertility Transition in New England: The Case of Hampton, N.H., 1655-1840,” in Generations and Change: Genealogical Perspectives in Social History, ed. Robert M. Taylor, Jr. and Ralph J. Crandall, Mercer University Press, 1986.

Krull, Catherine, and Frank Trovato. “Where Have All the Children Gone? Quebec’s Fertility Decline: 1941-1991.” Canadian Studies in Population 30:1:193-220, 2003.

Lindert, Peter, and Jeffrey Williamson. “American Incomes 1774-1860.” National Bureau of Economics Research Working Paper No. 18396, September 2012.

Margo, Robert. “Race and Schooling in the South: A Review of the Evidence.” In Race and Schooling in the South, 1880-1950: An Economic History, University of Chicago Press, 1990.

Markham, J. David. “The Revolution, Napoleon, and Education.” The Napoleon Series, napoleon-series.org.

Marlowe, Frank. “Hunter-Gatherers in Human Evolution.” Evolutionary Anthropology 14:54–67, 2005.

Matras, J. “The social strategy of family formation: some variations in time and space.” Demography 2:349-62, 1965.

Milot, Emmanuel, Francine Mayera, Daniel Nusseyb, Mireille Boisverta, Fanie Pelletierc, and Denis Réale. “Evidence for evolution in response to natural selection in a contemporary human population..” PNAS 108:41, October 2011.

Mullen, Lincoln. “Historical Religion Data in the NHGIS and What You Can Do with It“. October 2013.

Murdock, George. “The Common Denominator of Cultures.” In The Science of Man in the World Crisis, ed. Ralph Linton, pp. 123-142. New York: Columbia University Press, 1945.

Murphy, Tommy. “Old Habits Die Hard (Sometimes): Can département heterogeneity tell us something about the French fertility decline?.” No 364, Working Papers from IGIER (Innocenzo Gasparini Institute for Economic Research), Bocconi University, September 2012.

Parkerson, D.H., and Parkerson, J.A. “Fewer children of greater spiritual quality: religion and the decline of fertility in nineteenth-century America.” Social Science History12:1:49-70, Spring 1988.

Perry, Sarah. “Why People Used to Have Children“. The View from Hell, July 2014.

Perry, Sarah. “Children, Education, and Status.” The View from Hell, July 2014.

Raftery, Adrian, Steven Lewis, and Akbar Aghajanian. “Demand or Ideation? Evidence from the Iranian Marital Fertility Decline. Demography 32:2:159-182 , May 1995.

Schultz, T. Paul. “Fertility and Income.” Center for Discussion Paper 925, October 2005.

Somers, Angelo, and Frans Van Poppel. “Catholic priests and the fertility transition among Dutch Catholics, 1935-1970.” Annales de démographie historique 2:106:57-88, 2003.

Spolaore, Enrico, and Romain Wacziarg. “Fertility and Modernity.” Economics Department Working Paper, Tufts University, April 2014.

Van Bavel, Jan, and Jan Kok. “Birth spacing in the Netherlands. The effects of family composition, occupation and religion on birth intervals, 1820-1885.” European Journal of Population 20:119-140, 2004.

Wallace, R. Stuart, and Douglas Hall. “A New Hampshire Education Timeline.” The New Hampshire Historical Society.

Weiss, Volkmar. “The Population Cycle Drives Human History – from a Eugenic Phase into a Dysgenic Phase and Eventual Collapse.” MPRA Paper No. 6557, January 2008.