[Paleopsych] H-N: Nigel Barber: Evolutionary Explanations for Societal Differences in Single Parenthood

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Nigel Barber: Evolutionary Explanations for Societal Differences in Single 

[Thanks to Laird for this.]

    Evolutionary Psychology 3: 142-174

    Original Article

    Evolutionary Explanations for Societal Differences in Single

    Nigel Barber, Ph.D.,70 Kent Street, Portland, ME 04102, USA.


    The new research strategy presented in this paper, Evolutionary Social
    Science, is designed to bridge the gap between evolutionary psychology
    that operates from the evolutionary past and social science that is
    bounded by recent history. Its core assumptions are (1) that modern
    societies owe their character to an interaction of hunter-gatherer
    adaptations with the modern environment; (2) that changes in societies
    may reflect change in individuals; (3) that historical changes and
    cross-societal differences are due to the same adaptational
    mechanisms, and (4) that different social contexts (e.g., social
    status) modify psychological development through adaptive mechanisms.
    Preliminary research is reviewed concerning historical, societal, and
    cross-national variation in single parenthood as an illustration of
    the potential usefulness of this new approach. Its success at
    synthesizing the evidence demonstrates that the time frames of
    evolutionary explanation and recent history can be bridged.

    : Evolutionary Social Science; Evolutionary Psychology; Single
    Parenthood; Societal Differences; Historical Change; Adaptive
    Development; Sexual Development; Poverty; Values; Cultural Relativism;
    Sweden; England.


    Evolutionary psychology (EP) focuses on human adaptations to the
    hunter-gatherer way of life that is believed to have shaped human
    psychology over approximately two million years (Barkow, Cosmides, and
    Tooby, 1992; Buss, 1999; Cosmides, and Tooby, 1987; Durrant and Ellis,
    2003). This approach generally identifies evolutionary influences on
    modern behavior in terms of cross-cultural universals such as proposed
    universal sex differences in sexual jealousy and mate selection
    criteria (Geary, 1998) but recognizes that universal human
    characteristics, such as emotions, may find different expression in
    different societies (Fessler, 2004). It sees social sciences as
    falling within the natural sciences. By contrast, "standard" social
    science focuses on the present and attempts to account for behavioral
    variation in terms of contemporary influences without reference to the
    evolutionary past (Lopreato, and Crippen, 1999).

    Although the strategy of identifying universals at the level of
    information processing mechanisms of the brain was an important point
    of departure in the emergence of evolutionary psychology, this
    approach requires elaboration if it is to account for variation in
    modern behavior. Just as the social sciences are stuck in the present,
    so to speak, evolutionary psychology is focused on the evolutionary
    past. Admittedly many evolutionary psychologists have wrestled with
    the problem of how one gets from evolved psychology to modern behavior
    using constructs that include cognitive modules, Darwinian algorithms,
    memes, and so forth (Barkow, Cosmides, and Tooby, 1992). The new
    research strategy of evolutionary social science (ESS, Barber, 2005)
    strives to overcome the temporal problem (i.e., bridging the
    evolutionary past and the present) by using concepts of evolutionary
    adaptation to account for variation in modern behavior whether between
    siblings, between families, or between societies. This paper employs
    the new research strategy to organize data concerning single
    parenthood in a way that can stimulate new research.

    Before analyzing societal variation in single parenthood, it must be
    acknowledged that this new approach makes many controversial
    assumptions. It would be helpful to make these assumptions explicit
    and to explain briefly why they are necessary. The paper then shows
    how these assumptions help to organize data concerning single
    parenthood in different societies and at various points in history.

    The Assumptions of ESS

    ESS confronts evolutionary novelties in human social behavior produced
    by modern environments and thus aims to unite the evolutionary frame
    of explanation used by evolutionary psychologists and others with the
    historical time frame of many social sciences. To this end, it is
    necessary to make assumptions that have not been made previously, or
    at least not in an explicit and systematic way, with the aim of
    uniting the time frames of evolution and recent history. Some of these
    assumptions are sufficiently complex, problematic, and even counter
    intuitive, that they require some elaboration.

    Assumption 1: That modern societies owe their character to
    an interaction of hunter-gatherer adaptations with modern ecologies
    and environments. This assumption is fairly uncontroversial. However,
    as previously noted, existing social sciences generally do not connect
    modern life with evolutionary adaptations and are quite resistant to
    doing so.

    Assumption 2: Changes in societies may be caused by changes within
    individuals and they can affect individuals via bottom-up phenomena
    rather than via top-down transmission of values or behaviors
    . This form of reduction is actively resisted in some social sciences
    but it is worth emphasizing that scientific explanations almost always
    proceed by accounting for complex events in terms of more elementary
    constituents. Thus, the "behavior" of a molecule is always reducible
    to the characteristics of the constituent atoms.

    A particularly interesting example of individual change mediating
    societal differences is the way that sexual liberation of women in a
    particular society is related to an adverse marriage market that means
    women's individual chances of contracting a favorable marriage is
    bleak, so that they must assert themselves in the monetary economy
    through paid employment or operation of businesses (Barber, 2002 a,
    2004 a; Guttentag, and Secord, 1983). This phenomenon is by no means
    recent, cropping up in 14th-century England, and classical Sparta, for
    example. To say that social change in such cases is caused by forces
    acting at the individual level might seem like a semantic exercise
    given that the marriage market difficulties of females is distributed
    throughout the society but ESS opts to use individual-level
    explanations of social arrangements because these are theoretically
    relevant, viable, and scientifically plausible.

    Assumption 3: that historical changes and cross-societal differences
    are due to similar adaptational mechanisms.
    This assumption contradicts the argument of cultural relativism. This
    is not to deny that all societies have some unique features, such as
    the peculiarities of their language communication system, their forms
    of dress, body ornamentation, basketry, pottery design, and so forth.
    Rather, the argument is made that to the extent the phenomena are
    truly unique, they defy scientific explanation and are thus of minimal
    interest to scientists, as opposed to artists, for example. One
    practical ramification of Assumption 3 is that historical mechanisms
    can be studied indirectly through cross-societal comparisons of
    contemporary peoples. To take a simple example, the high fertility of
    women in Africa today is due to the same agricultural mode of
    production that supported the majority of American women a century
    ago, and was associated with high fertility for them also.

    Assumption 4: that different social contexts (e.g., social status)
    modify psychological development through adaptive mechanisms
    . This can be considered a general theory of psychological development
    that not only accounts for the adaptive match between individual
    behavior and the social environment, but also helps to explain
    historical, and cross-national societal differences. This assumption
    can be rephrased as an expectation that certain social inputs during
    development shall produce specific behavioral/psychological outcomes.
    For example, corporal punishment increases interpersonal aggression,
    helping to explain why parents in warlike societies are more likely to
    use harsh disciplinary tactics on their sons (Ember and Ember, 1994).
    Similarly, there is evidence that reproductive behavior, including
    single parenthood, is affected by childhood stressors.

    Childhood Stress, Divorce, and the Development of Reproductive

    Psychological stress in childhood influences adult sexual psychology
    and behavior in part because it alters brain development. Poverty is
    one example of a complex stressor in modern societies and researchers
    recently discovered that childhood stress alters brain structures and
    thus potentially modifies the sexual psychology of males and females
    (Teicher, Anderson, Polcari, Anderson, and Navalta, 2002). Brain
    biology is far from being the complete picture, of course, and
    marriage is greatly affected by the availability of suitable partners,
    for example. Whatever the underlying mechanisms, men raised in poverty
    are less likely to provide, and women are less likely to require, the
    emotional commitment and economic support for children that are
    characteristic of the marriage contract around the world, so that
    single parenthood is correlated with low income within a country.

    Poverty is not the only source of childhood stress, of course. If
    psychological stress affects sexual development and reproductive
    behavior in predictable ways, then other sources of childhood stress
    would be expected to have similar consequences for adult sexual
    behavior. Parental divorce is an interesting type of childhood
    stressor in this context because it is more of a middle-class
    experience in the U.S., for example, not because poor people enjoy
    stable marriage, but because they are considerably less likely to wed
    in the first place (Abrahamson, 1998). Although children of divorced
    parents experience a modest decline in living standards, they remain
    much better off, on average, than children raised from the beginning
    by single mothers (Waite and Gallagher, 2000). This means that divorce
    offers a useful window into the effects of psychological stress,
    unalloyed with extreme economic deprivation, on the development of
    sexual behavior.

    Wallerstein and Blakeslee (1996) concluded that most American children
    who experience a bitterly-fought parental divorce suffer lifelong
    problems in forming committed sexual relationships. Their conclusion
    is supported by the following data on children of divorced parents
    (Wallerstein, 1998):

    Females are approximately 50% more likely to give birth as teens.

    They are approximately 48% more likely to divorce themselves (60% for
    white women and 35% for white men).

    Their marriages may be either highly impulsive (particularly for
    females), or delayed due to lack of self-confidence and trust
    (particularly for males). About a quarter of children of divorced
    parents (24%) never marry compared to one in six (16%) for the general
    population, suggesting a lack of trust in intimate relationships.

    They suffer from emotional problems (e.g., depression, behavioral
    disorders, learning disabilities) at a rate that is two-and-a-half
    times that of the general population.

    Correcting the divorce rates by the marriage rates, it can be
    estimated that children of divorced parents have only about a
    one-in-five probability of being stably married, compared to a
    two-in-five chance for the general population (assuming a non-divorce
    rate of .50 multiplied by a marriage rate of .84). Compelling as such
    numerical differences are, they nevertheless minimize the relationship
    correlates of parental divorce because they leave out the emotional
    pain, anxiety, conflict, and self-doubt, that Wallerstein's informants
    described during lengthy interviews in the context of protracted
    longitudinal research.

    Even those who contributed to stable marriage statistics were often
    far from happy in their union. According to Wallerstein and Blakeslee
    (1996), the facade of marital permanence frequently concealed much
    discontent. Low expectations, combined with a sense of helplessness,
    often kept children of divorced parents in wrenchingly discordant
    marriages that more confident individuals might have changed, or

    Evidently, conflict and unhappiness in the parental marriage creates
    an expectation in children that their own marriages may be discordant,
    or fail. Males and females often respond differently to parental
    conflict (Barber, 1998 a, b; Wallerstein and Blakeslee, 1996). Young
    women may react to parental friction and separation with precocious
    sexuality. They initiate sexual activity sooner, and may even reach
    sexual maturity earlier, compared to young women raised in intact
    marriages (Ellis, 2004; Ellis, Bates, Dodge, Fergus, Horwood, Petit,
    et al., 2003). These phenomena help to explain the higher rate of teen
    pregnancy and childbearing among children of divorced parents.
    Marriages are often early, and impetuous, as well.

    In the absence of a reasonable period of courtship in which the couple
    get to know each other, and conduct a protracted evaluation process,
    marriages are liable to be incompatible, and unstable. Early marriages
    are also more likely to end in divorce. While the young women may
    enter marriage recklessly, Wallerstein and Blakeslee (1996) describe a
    rather different type of commitment problem as characteristic of male
    children of divorced parents. These may experience lifelong
    difficulties in expressing, or even acknowledging, their emotions,
    which impedes sexual relationships and militates against happiness in
    a marriage. Many fear intimacy and postpone committed relationships
    (Barber, 1998a, b).

    Some children may feel so traumatized by parental divorce that they
    are inclined to postpone marital commitment (Wallerstein and
    Blakeslee, 1996) preferring to cohabit before marriage (Whitehead and
    Popenoe, 2002). For individuals who fear marital commitment, this
    might seem a sensible way of progressing to a more committed, more
    permanent relationship. Informal unions are highly unstable, however,
    (Smock, 2000) possibly because of the lack of commitment with which
    they begin (Waite and Gallagher, 2000).

    Wallerstein and Blakeslee (1996) serve rather like a Greek chorus in
    emphasizing the tribulations inflicted on children by parental
    divorce. By contrast Hetherington and Kelly (2002), serve as
    cheerleaders for children's powers of recovery following parental
    divorce. Hetherington collected data on some 1,400 families and their
    2,500 children spanning three decades, focusing on objective facts
    rather than the more subjective interview techniques employed by
    Wallerstein on smaller samples. Hetherington found that the majority
    of children are resilient and bounce back from the distress of
    parental divorce in a few years without experiencing major behavioral
    or emotional problems.

    Hetherington's optimistic conclusions are summarized in a Time
    magazine interview (Corliss, 2002): "A lot of the current work makes
    it sound as if you've given your kids a terminal disease when they go
    through a divorce. I am not pro-divorce. I think people should work
    harder on their marriages: support each other and weather the rough
    spots. And divorce is a painful experience. I've never seen a
    victimless divorce - where the mother, father, or child, didn't suffer
    extreme distress when the family broke up. But 75% to 80% do recover."
    p 40

    By "recovery" Hetherington means the absence of serious psychological,
    social, or emotional problems that would warrant professional
    attention. Given that 75% of children "recover" by this definition,
    25% experience serious emotional problems, compared to 10% of children
    from intact two-parent families. In other words, their risk of serious
    emotional problems is more than doubled. In addition to those
    individuals with diagnosable psychological problems in the years
    immediately following parental divorce, many others could have serious
    lifelong problems in forming happy and committed reproductive
    relationships. These problems are at least partly attributed to the
    stress of parental divorce, although other environmental factors, such
    as social learning and inadequate opportunities to acquire social
    skills cannot be ruled out.

    Genetic influences may also matter. This point is most clearly
    established in research finding an association of the androgen
    receptor gene with aggression, impulsivity, and number of sexual
    partners, and parental divorce for both sexes as well as female age of
    menarche (Comings, Muhleman, Johnson, and MacMurray, 2002), although
    the effect sizes were modest. Yet, the problems of children of
    divorced parents are not just a product of inheriting "hostile" or
    "emotionally troubled" genes from parents. This conclusion emerges
    from behavior genetics research comparing outcomes for adopted
    children with those of biological children subsequent to parental
    divorce. Adoptees suffer more from emotional problems following
    parental divorce even though they share no genes with the divorcing
    parents (O'Connor, Caspi, DeFries, and Plomin, 2000). Quinlan's (2003)
    analysis of data from the National Survey of Family Growth also found
    that parental separation before the age of five years predicted early
    menarche, age of first pregnancy, and shorter duration of first
    marriage. Parental separation during adolescence was more strongly
    predictive of number of sex partners, however, suggesting that changes
    in care-taking arrangements have complex age-dependent effects on the
    development of sexual and reproductive behavior. If the stress of
    parental divorce and/or separation can have substantial effects on
    marital commitment in the second generation, it is not hard to imagine
    that the multiple stresses of poverty could have comparable effects on
    sexual behavior and marriage (see below).

    In summary, a stressful early childhood increases the probability of
    single parenthood because of the resulting difficulty in forming
    committed reproductive relationships. This is true of parental
    conflict surrounding divorce, but it may also be linked to childhood
    poverty, or other causes, thus implicating developmental changes in
    the brain. On the other hand, single parenthood may occur at high
    levels in societies where children are exceptionally well off, and do
    not have highly stressful childhoods, as is true of Sweden, for
    example, pointing to multiple causation.

    Nonmarital reproduction is a complex phenomenon that reflects the
    reproductive strategies, and sexual behavior, of both sexes. These are
    affected in interesting and complex ways by economic influences and
    marriage markets, as illustrated by research on the history of single

    Poverty and the History of Single Parenthood

    Poverty can affect reproductive behavior in two different ways each
    suggesting adaptive design: through the effects of stressors on brain
    development; and through its effects on marital opportunity. There is
    abundant historical evidence that poverty was an important influence
    on single parenthood because of its limiting effects on marital
    opportunity due to scarcity of men who were economically qualified for
    marriage. Even today, depressed economic conditions around the world,
    and high male unemployment, occur in nations that have high ratios of
    nonmarital births (Barber, 2003 c). Historical evidence indicates that
    the reproductive practices of young people in respect to nonmarital
    childbearing were affected by economic circumstances (Abrahamson,

    Economic determinism is not the only possible explanation for
    historically changing single parenthood ratios, of course. Many social
    historians, believe that changes in single parenthood ratios are due
    to changing degrees of sexual liberation. Thus, the steady rise in
    single parenthood ratios for many European countries throughout much
    of the 19th century is attributed to increasing sexual liberation
    associated with industrialization of the economy and urbanization of
    the population. There is little doubt that changes in single
    parenthood ratios of this period were genuinely connected to the
    ongoing Industrial Revolution but appealing to sexual liberation as
    the cause falls short as a scientific explanation, particularly
    failing to explain historical changes in sexual attitudes, as
    explained in more detail below.

    The increase in single parenthood during the 19th-century period of
    industrialization may be illustrated by the case of France where
    single parenthood ratios rose from about 5% of all births at the
    beginning of the century to about 10% at its end (Shorter, 1975). The
    largest increase in single parenthood occurred in cities, such as
    Paris and Bordeaux, where illegitimacy ratios surged above 30%,
    comparable to the level seen in many modern cities. Other European
    cities manifested a similar rise in single parenthood, partly
    reflecting an increase in the number of young single women who
    migrated to cities and towns in response to job opportunities
    associated with urban development following the Industrial Revolution.

    There are many reasons why urbanization may increase single
    parenthood. Thus, living in an unfamiliar social environment, young
    women may have experienced difficulty in finding husbands. This
    problem was exacerbated by an excess of single women to single men
    (because young males were more likely to remain at home to work on
    family farms). The same phenomenon is still in evidence in modern
    cities where the feminine population generally exceeds the masculine
    one (Guttentag and Secord, 1983). Thus, for U.S. metropolitan areas,
    there are just 93 males over the age of 16 years per 100 females when
    people living in prisons, and other institutions, are excluded
    (Barber, 2002d).

    European single parenthood ratios increased during the 19th century,
    until about 1880, when a decline began that lasted for over two
    decades (Shorter, 1975). This decline was accompanied by a decrease in
    marital fertility, and both phenomena evidently reflect use of
    condoms, or other contraceptive devices, that became widespread about
    this time (Langford, 1991).

    The sharp and widespread increase in single parenthood following the
    industrial revolution is apparently without historical precedent and
    thus a challenge for historians as well as ESS. Many historians see
    increased single parenthood as a product of sexual liberation (or
    moral degeneration, depending on their perspective).

    According to the sexual liberation argument, urbanization brought
    large numbers of lustful young men and women together in an
    environment where the watchful eyes of relatives, and other
    traditional constraints on sexual behavior no longer mattered. They
    converted newfound sexual opportunity into sexual expression outside
    marriage thereby boosting illegitimate births.

    The sexual liberation interpretation may well describe changing
    patterns of sexual behavior but it is far from satisfying when judged
    by the criteria of a scientific explanation for those changes. One
    problem is circularity. Sexual liberation is defined by an increased
    probability of sex outside marriage. For much of the 19th century,
    prior to widespread use of contraceptives, increased extramarital
    sexuality produced an inevitable rise in single parenthood. (It is
    true that premarital conceptions could be, and often were,
    legitimized, by marriage, however). If such complications are set
    aside, attributing increased ratios of single parenthood to sexual
    liberation is largely an exercise in circular reasoning. If we did not
    have data on single parenthood, we might not know that sexual behavior
    was "liberated." Other clues of such trends may be uncovered by
    historians, of course, including explicit depictions of sexual
    behavior in the arts and literature, or an increase in tax revenues
    from prostitution, but such measures of sexual liberation often lack
    the consistency and validity of the illegitimacy ratio itself.

    Strictly speaking, scientific explanation requires that the
    explanatory variable be measured independently of what is being
    explained, a criterion that is often lacking in social research. Yet,
    it is disputable whether sexual liberation can be reliably measured in
    historical research without referring to the illegitimacy ratio. If
    sexual liberation cannot be separated from single parenthood, then one
    phenomenon cannot be used as a scientific explanation of the other:
    they are not independent. Explaining one in terms of the other is thus
    an exercise in circular reasoning.

    Even if sexual liberation could be measured independently of
    premarital sexuality, there is still a problem about direction of
    causation between attitudes and behavior. Do sexually liberated
    attitudes cause sexually liberated behavior, or do attitudes conform
    to behavior? A large technical literature on the connection between
    sexual attitudes and behavior suggests that both directions of
    causation might apply (Moors, 2000). Young women who cohabit become
    more sexually liberated in their attitudes following this experience,
    for example. Such evidence once again highlights the difficulty of
    establishing scientific independence between attitudes of sexual
    liberation and sexually liberated behavior.

    The sexual liberation hypothesis of increasing single parenthood with
    urbanization is not a genuine explanation: it does not provide a
    causal explanation for this historical change. Even if one admits that
    female residents of Paris produced 30% of their offspring outside
    wedlock in 1880 due to sexual liberation, this does not solve the
    fundamental problem of why Parisiennes were so much less liberated a
    century earlier when nonmarital birth ratios were below 5%.

    Sexual liberation interpretations may deflect attention away from the
    real drivers of historical change, of which economic factors seem
    particularly important. The influence of economic constraints on
    family formation is well illustrated by English historical research
    dealing with local increases in nonmarital birth ratios (Abrahamson,

    Historical "Outbreaks" of Single Parenthood in English Communities

    Single parenthood is rarely even mentioned by anthropologists,
    suggesting that it would have been difficult for women in the
    evolutionary past to raise children alone. Similarly, throughout the
    era of written history, single parenthood was not a practical
    alternative and was chosen only as a last resort by women who failed
    to marry. In addition to the economic difficulties of single
    parenthood, illegitimate children were at a real social disadvantage
    in England. They were stigmatized, or ostracized, and suffered real
    legal disadvantages in the sense of not being able to inherit
    property, for example. The great majority of English women, typically
    in excess of 95%, were married when they gave birth, suggesting that
    the minority of single mothers were victims of ill fortune due to
    unintended pregnancy combined with an inability to demand marriage
    from the father (Shorter, 1975).

    In such a social environment, women raised children alone only for
    lack of a better alternative. Marriage prospects were severely
    curtailed by economic problems. This phenomenon is illustrated in
    English history, where crop failures forced couples to delay marriage
    because they lacked the economic resources to set up an independent
    household. If they were sexually active before marriage, this meant
    they were at greater risk of producing out-of-wedlock births.

    When Abrahamson (2000) examined historical surges in local
    out-of-wedlock birth ratios in England between 1590 and 1985, he found
    that all eleven cases of high nonmarital birth ratios followed an
    economic downturn. This phenomenon may be illustrated by the case of
    Terling, a small agricultural community 30 miles northeast of London.
    Between 1560 and 1590, nonmarital births were low, even by historical
    standards, constituting between 1% and 2% of total births. The
    illegitimacy ratio rose between 1590 and 1605, when it reached 10%.
    Abrahamson attributes this increase to an economic phenomenon that is
    familiar from more recent periods, namely price inflation.

    Terling's economic problems began in the 1580s and can be traced to
    population growth. With more mouths to feed, and an increased demand
    for food, prices soared. Price inflation eroded the purchasing power
    of wages, making it difficult for the landless poor, to make ends
    meet. This bad food scarcity was aggravated by a series of crop
    failures during the 1590s. The worsening economic situation made it
    economically impossible for many young couples to marry, and set up
    households, even if the woman was pregnant.

    Being an unmarried mother invited legal sanctions and pregnant women
    could be punished, for immorality, or "fornication." At the peak of
    the illegitimacy "outbreak," legal enforcement was comparatively lax.
    Only a third of unmarried pregnant women were prosecuted, compared to
    three-quarters of them in more normal times. Many women were excused
    prosecution on the understanding that they would marry when their
    fortunes improved. This comparative leniency evidently reflected some
    understanding that marriage was constrained by difficult economic
    circumstances. When the economy improved, fornication laws were
    enforced more rigidly again. A similar change occurred in respect to
    enforcement of prostitution laws. In the difficult period after 1590,
    when few young men were marrying, and the services of prostitutes were
    in high demand, enforcement of vice laws was also relaxed, providing
    further evidence of the plasticity of moral, and legal, codes in the
    face of changing economic conditions (Abrahamson, 2000).

    The constraints faced by young women in 16th-century England are
    obviously very different from the situation of modern women. The use
    of effective birth control, for example, means that single women are
    quite unlikely to become pregnant as a result of delayed marriage
    today. Even so, economic conditions affect the marriage market and
    single parenthood ratios of the 20th century in complex ways. This
    phenomenon has often been highlighted in connection with the marriage
    difficulties of African American women, for example.

    African American scholars, including Wilson (1997), emphasize the
    impact of declining job prospects for African American men on single
    parenthood. He points to the decline in well-paid blue-collar
    manufacturing jobs in the U.S. after about 1950. Many African American
    men were subsequently forced into poorly-paid dead-end service jobs
    that provided little chance of supporting a family. According to
    Wilson, this meant that a large proportion of African American men
    were economically disqualified from marriage. The scarcity of men who
    were economically qualified for marriage was exacerbated by a host of
    other factors, reducing the availability of men for marriage. They
    included: low sex ratios at birth, higher mortality of young men,
    marriage of more black males than females outside their ethnic group,
    and high rates of incarceration in prisons. In 1950, for example,
    there were approximately 70 employed men aged 20-24 years per 100
    same-aged women (Staples, 1985). Thirty years later, in 1980, there
    were only, 50 marriageable men per 100 women in this age category.

    Other research supports the hypothesis that reduced marriage
    opportunities of African American women play an important role in
    accounting for their high single parenthood ratios. Thus, African
    Americans living in metropolitan areas where there is a scarcity of
    marriageable men have higher ratios of single parenthood (Fossett, and
    Kiecolt, 1991). Based on state-level data, South and Lloyd (1992)
    found that ratios of nonmarital births decline with increases in
    availability of marriageable men (as indexed by the sex ratio). South
    (1996) found, however, that although young women were more likely to
    marry as the availability of males increased, increases in the
    proportion of males in high schools increased the chances of single
    parenthood, a puzzling result that is inconsistent with the rest of
    the literature. Births to African American teens (the great majority
    of which are to single mothers) were also predictable from reduced
    mate availability according to research comparing U.S. metropolitan
    areas (Barber, 2002b) and states (Barber, 2002c) in analyses that
    controlled for poverty and unemployment.

    The same economic principles thus help explain why single parenthood
    was common among 20th-century African Americans as well as 16th
    century farmers in England. A similar logic applies to poor
    20th-century European Americans also. In some economically depressed
    White neighborhoods, including the lower end of South Boston the
    majority of children are born outside marriage (73% in 1990, Whitman,
    1996). Where there is a severe scarcity of marriageable men, (which is
    more likely in poor communities), women must choose between raising
    their children outside marriage or forgoing reproduction altogether.

    The marriage market, and the economic variables affecting it thus
    provides a good understanding of historical changes in single
    parenthood. This conclusion is also supported in time series analysis
    of single parenthood in England, Scotland, and the U.S. (Barber, 2004
    a). A similar pattern emerges from cross-national studies, as well as
    comparisons among U.S. states and metropolitan areas (Barber, 2000 a,
    2000 b, 2001, 2002 a) that controlled for numerous variables such as
    female literacy, contraception use, poverty, unemployment,
    incarceration rates, and so forth. Whatever unit of analysis, or time
    period, is studied, the data are consistent in showing that young
    women who face a scarcity of marriageable men are more likely to begin
    their reproductive careers early in life and to raise their children
    with minimal paternal investment, consistent with the anthropological
    conclusion that if men cannot be relied upon to provide long term
    parental investment women gravitate to earlier reproduction (Draper
    and Harpending, 1982).

    The data on single parenthood are thus consistent with assumption 3,
    stating that historical changes and societal differences are due to
    the same mechanisms. Of course, these data do not guarantee such
    uniformity for other areas of study but they do at suggest that ESS is
    a workable research strategy.

    Environmental influences on reproductive strategies do not end with
    the marriage market, of course. Within a society, or community,
    particular individuals are more or less likely to form long-term,
    committed, romantic relationships depending, in part, on their
    childhood experiences, including the stresses of poverty (or parental
    divorce). This phenomenon thus provides a concrete example of
    Assumption 4 -- that different social contexts modify psychological
    development adaptively.

    Poverty and the Emotional Basis of Single Parenthood

    There is no doubt that economic disadvantage impaired marriage
    formation over many centuries of European history. A crucial question
    to ask in this connection is whether individuals make adaptive
    emotional adjustments that allow them to fit in with an environment of
    reduced marital opportunity for either sex. Perhaps surprisingly,
    there is fairly good evidence that the emotional development of the
    individual is modified in ways that help her, or him, to fit in with
    economic, and romantic, limitations of the local environment.

    To begin with, one finds that the emotional tone of low-income
    households is very different from that of more affluent ones. Poverty
    is accompanied by greater emotional negativity in the home as revealed
    by research on content analysis of speech, problem-solving by
    children, child abuse, antisocial behavior, mental illness, and so on
    (Barber, 2002 a; Hart and Risley, 1995]. Exposure to negative
    emotionality in early life evidently reduces trust, and commitment, in
    future relationships, particularly intimate ones, like close
    friendships and marriage (Belsky, Steinberg, and Draper, 1991). If
    poor children experience more emotional negativity in early life, does
    this mean that they have greater difficulty in establishing the trust
    required for stable reproductive relationships? Is poverty within a
    society a useful predictor of individual differences in emotional
    commitment problems?

    One way of assessing this question is to investigate the effects of
    parental income on single parenthood ratios in cross-sectional
    research. If women are raised in poverty are they more likely to
    reproduce as single mothers, all else being equal?

    Based on the theoretical perspective of Belsky, et al., (1991) and
    assuming that poverty is psychologically stressful (Lupien, King,
    Meaney, and McEwen, 2001), one would predict that poverty should evoke
    emotional negativity during childhood, thereby increasing subsequent
    emotional commitment problems, so that people raised in poverty would
    be more likely to be single parents.

    Poverty can be measured indirectly in terms of low educational
    attainment given that education affects a person's earning potential
    in our society. Low education level is a powerful predictor of single
    parenthood. Using education level as a proxy measure, it turns out
    that poor women are considerably more likely to have out-of wedlock
    births. According to U.S. data for 1994, 46% of the children born to
    female high school dropouts were outside wedlock, as opposed to just
    6% of children born to women with a bachelor's degree. (Respective
    proportions for high school graduates and women with some college were
    30% and 17% respectively Abrahamson, 1998). Similar patterns apply to
    single fathers. These results suggest a remarkable bifurcation in
    American society whereby affluent, well-educated, women maintain
    single parenthood ratios that are not appreciably different from
    historical norms whereas poor women demonstrate a huge increase in
    single parenthood, consistent with the emotional development thesis.
    Of course, poor women are also more likely to raise children alone
    because they encounter fewer men in their social circles who are
    economically qualified as marriage partners.

    Although historical research on single parenthood emphasizes the
    economic characteristics of males, the greater participation of modern
    women in paid labor means that their own economic opportunities are an
    increasingly important influence on family structure. Broadly
    speaking, there are two distinct subtypes of feminine economic
    independence. Close to the top of the economic hierarchy, women have
    the option of raising children independently, although this option is
    less desirable in some countries than others for various economic and
    political reasons, such as government contributions to child support.
    "Murphy Browns" are thin on the ground in the U.S., for example but
    evidently much more common in social democratic countries like Sweden.
    Closer to the bottom of the economic hierarchy, poor women may be
    independent of paternal support of children by necessity, i.e., there
    is a scarcity of economically qualified men.

    As these notions imply, wealthy women are more likely to begin their
    careers as single mothers comparatively late in life, after they have
    established themselves in careers, (which typically takes some ten
    years of effort; Goldin, 1995; Kaplan, Lancaster, Tucker, and
    Anderson, 2002), whereas poor women are more likely to begin their
    reproductive careers as single mothers earlier in life.

    Interestingly, a young woman's career prospects can have a major
    influence on when she begins her family. One of the best measures of
    career potential is academic success in high school and academic
    failure greatly increases the probability of single teen childbearing.
    Data from the National longitudinal Study of Youth indicate that women
    aged 15-19 yr at the bottom fifth of their high school class in math
    and reading skills are five times more likely to bear children
    compared to those in the top fifth (15% compared to 3% per year,
    Pittman and Govan, 1986). Although most teen pregnancies are
    unplanned, career motivation affects deliberate reproductive choices
    in predictable ways. Thus, when teens having high career aspirations
    find themselves pregnant, they are more likely to have an abortion.
    Young women with low career aspirations are more strongly motivated to
    invest their time and energy in raising a child (Barber, 2000 a,
    Pittman and Govan, 1986).

    Despite efforts in many social democratic countries of Europe to ease
    conflicts between work and family, there is often a clash between
    raising children and developing a career. This conflict may be deduced
    from the fact that career women postpone reproduction for
    approximately a decade compared to those without careers (defined as
    earnings above the lowest 25%, Goldin, 1995).

    The conflict between careers and early reproduction is thus fairly
    straightforward and can be thought of as partly a product of
    conflicting time demands between career and family. The connection
    between educational failure and early reproduction of single women is
    rather more complex.

    To begin with, sub par educational performance predisposes young
    women, particularly poor ones, to early sexuality for a variety of
    reasons. Early single parenthood is facilitated not just because of
    bad career prospects but also by diminished opportunities for

    The role of poverty in diminished marriage prospects may be
    illustrated by comparing various U.S. ethnic groups that differ in
    average earnings. One measure of marriage difficulty is the proportion
    of women who reach the end of their reproductive lives without
    marrying. By the age of 40-44 years, 22% of African American women
    have never married, compared to just 7% of whites and 10% of Hispanics
    (Abrahamson, 1998). The poorer groups, (African Americans and
    Hispanics), thus have substantially higher rates of non marriage
    compared to Whites. These data constitute a very conservative measure
    of marriage problems among poor women, however. Thus, although the
    great majority of Black women eventually marry, they are likely to be
    unmarried when their first child is born and spend much of their peak
    reproductive years as single mothers due to delayed marriage and to
    marital instability.

    Data on first births before marriage provide a clearer picture of the
    marriage market difficulties of poorer U.S. ethnic groups. Between
    1990 and 1994, three quarters of African American first births were
    before marriage compared to two-fifths for Hispanics, and a quarter
    for whites (Abrahamson, 1998). Women from poorer ethnic groups are
    thus considerably less likely to marry before giving birth for the
    first time. Note that African American women are considerably more
    likely to be single at the time of their first birth compared to
    Hispanics although there are minimal differences in income, that
    actually favored African Americans at this period. These differences
    probably reflect the scarcity of young males in African American
    communities due to early deaths, illnesses, accidents, and
    incarceration, among other factors (Barber, 2002a).

    In addition to the adaptive pattern of relationships between single
    parenthood and economic factors (including the marriage market)
    children raised in poverty generally experience a psychologically
    harsher early life that militates against the trust, commitment, and
    empathy, that form the basis of successful marriages (see below).
    Alternatively stated, in an environment where marriage is less viable
    as a reproductive strategy, children mature with less interest in, or
    potential for, stable romantic relationships. This suggests that
    children are raised to fit in with the practical realities of adult
    life in their particular community. In other words, it suggests
    adaptive flexibility in the development of human sexual behavior.
    Further evidence for this interpretation is provided by research on
    the development of sexual behavior as a function of parental income.

    Poverty and Adaptive Flexibility in Sexual Development

    One way in which poverty affects single parenthood is clearly through
    the limitations it places on marriage formation, as illustrated both
    by historical and contemporary research using various methodologies.
    Sexologists have long been aware of differences in sexual behavior as
    a function of socioeconomic status and it seems reasonable to classify
    such differences as manifestations of a more general phenomenon of
    adaptive flexibility in sexual development. Generally speaking, being
    raised in poverty predisposes men to short-term relationships, or the
    low-investing "cad" strategy described by evolutionary psychologists
    (as opposed to the high-investing "dad" strategy, (Cashdan, 1993;
    Draper and Harpending, 1982). Men would not succeed in their career as
    cads if this were not tolerated, or even encouraged, by women having a
    similarly short-term perspective on sexual relationships, however.

    This argument is clearly supported by anthropologist Elizabeth
    Cashdan's (1993) research on sexual strategies of college students.
    She found that women's and men's sexual behavior varies considerably
    as a function of their expectations about masculine commitment in
    sexual relationships. Cashdan concluded that the less emotional
    commitment women expected from men in their dating pool, the more
    short-term their own perspective was. Women who believed that their
    dating environment was full of cads, dressed provocatively, and had
    many sexual partners. On the other hand, if they encountered many
    potential dads, i.e., caring and nurturing men, they behaved more
    sedately, emphasizing their own propensities for sexual fidelity and
    chastity. Cashdan reported that cads attracted women by drawing
    attention to their physical appearance, and sexuality, whereas dads
    "advertised" their economic assets, or capacity for economic success,
    as well as their desire for a permanent relationship. While some
    readers might see such findings as confirming outmoded stereotypes of
    sex differences in sexual behavior, it is important to recognize that
    college students, as a group, are arguably more immune from
    preconceived notions about sexual behavior than other segments of the
    population and are thus expressing evolved psychological propensities
    within this particular environment (see Townsend, 1998, for a similar
    argument concerning medical students).

    While young college students adapt their dating behavior to the
    immediate social environment, it is quite clear that some of the
    variation in sexual behavior is also affected by the developmental
    environment (as well as genetically inherited variation, Simpson and
    Gangestad, 1992). Thus, a more stressful early environment predisposes
    people to short-term, or unstable, sexual relationships, as manifested
    by the data on children of divorced parents, for example. Other
    complex childhood stressors, specifically poverty, may have similar

    Most theories of the influence of stressful home environments on the
    development of sexual behavior emphasize the pathological aspects, as
    reflected in social problems like school failure, delinquency, and so
    forth. Evolutionists are more willing to accept that there is a range
    of adaptive variation, and that children's responses to stressful
    rearing experiences may constitute normal function in an adverse
    environment rather than the breakdown of normal developmental

    To this end, Belsky, et al. (1991), proposed that children who
    experience insensitive parenting, which is more characteristic of
    low-income homes, are better prepared to prosper in a harshly
    competitive adult social environment. Belsky et al.'s evolutionary
    theory of socialization pivots on the principle that unresponsive
    parenting elicits exploitative interpersonal attitudes and antisocial
    behavior in the second generation. It also produces a short-term
    perspective towards sexuality.

    Given that poverty is associated with increased psychological stress
    among children, it would be predicted to have all of the above
    effects. The most compelling evidence of emotional negativity in
    parent-child relationships in poor homes comes from analysis of actual
    speech content addressed to children in economically disadvantaged
    homes. Parents provide far less verbal stimulation to children in poor
    homes, which has important implications for cognitive development in
    general, and for the development of vocabulary size in particular.
    Poor parents say much less to their children and what they do say is
    much likely to have a hostile, emotionally negative, or disparaging,
    tone, to involve scolding rather than praise (Hart, and Risley, 1995).
    The implied relative lack of emotional warmth between parents and
    children has rather obvious implications for future sexual

    Thus, poor single teenage mothers often complain about a lack of
    warmth in relations with mothers according to Musick (1993). Research
    on the home backgrounds of single teen mothers finds that they
    experience many psychological stresses, and sources of negative
    emotionality, when compared to non mothers (Corona, and Tidwell,
    1999). Family problems included: the absence of a father figure to
    provide emotional and economic support; arguments between parents;
    exposure to drug addiction or alcoholism in the home; parental
    divorce; physical, sexual, or emotional abuse; and unsatisfactory or
    unstable relationships with foster homes.

    Separation from fathers (which occurs more commonly in low-income
    homes) may engender a sense of emotional deprivation for which early
    sexual relationships seem to provide an answer. The likelihood of
    young women being sexually active at an early age, and becoming
    pregnant in teenage years, is increased by a perceived lack of
    emotional closeness to their mothers. Many teen mothers describe the
    relationship with their own mothers as both difficult and distant in
    interview studies. Some of the mothers are emotionally rejecting and
    others emotionally dependent on their daughters (Corona, and Tidwell,
    1999}. Psychologists find that father absence does not have the same
    consequences where it is due to bereavement, suggesting a complex
    interaction of factors in the family environment on emotional
    development (Barber, 2000 a; Popenoe, 1996).

    Unsatisfying emotional relationships with parents may produce complex
    effects on sexual psychology. Many young single mothers have
    conflicting attitudes to men. Perhaps, consistent with what they may
    have witnessed around their own homes, they view most men as
    unreliable, alcoholic, and potentially violent. Conversely, they may
    entertain unrealistically favorable expectations of their own
    partners, hoping that once they become pregnant, their boyfriend will
    fall in love with them and propose marriage. Anderson (1990) paints a
    vivid picture of the short-term sexual relationships conducted by
    young African American mothers inhabiting economically depressed inner
    cities where marriage prospects are diminished by unfavorable economic
    conditions as well as the scarcity of men. Anderson describes dating
    in this environment as an odd mixture of calculation and vulnerability
    wherein young women use their sexuality to manipulate men and often
    end up pregnant and abandoned. His "streetwise" young men are
    portrayed as befriending women purely to obtain sexual gratification
    that they refer to as "hit and run" or "booty." To accomplish their
    short-term sexual goals, men cater to female fantasies by offering
    extravagant, if insincere, promises of affection, love, and even
    marriage. After a young woman finds herself pregnant, she is likely to
    be abandoned, with contempt. The relationship ends and the cycle
    begins anew with a different partner. Playing their role as cads to
    perfection, the "streetwise" man refuses to support the children he
    has fathered. Where women perceive their world to be full of cads,
    they also employ short-term reproductive tactics, emphasizing their
    physical attractiveness and using their sexuality as a bargaining chip
    to obtain the attention and fleeting affections of men (Cashdan,

    Short-term reproductive strategies are clearly not peculiar to
    America's inner city but can be seen as an adaptive response to
    difficult economic circumstances in any country. Sex researchers
    working in the U.S., and Britain, found that working class people, or
    low-income people, were generally more unrestrained in their sexual
    attitudes and behavior compared to the rest of the population. During
    the 1960's, middle class youth tended to catch up with their working
    class counterparts in terms of premarital sexuality, and other
    measures of sexuality, however. English research conducted in the
    1960s and 1970s nonetheless found that income-group differences
    persisted in the sense that working class youth were sexually active
    from an earlier age. (Argyle, 1994)

    Eysenck (1976), reported that working class Britons were more likely
    to approve of marital infidelity and to agree that physical
    gratification is the most important aspect of marriage. He concluded
    that working class respondents to surveys are more earthy whereas
    middle class respondents are more moral in their sexual attitudes.
    Eysenck believed that working class people had more libido. American
    research conducted at the end of the 1980s reached similar
    conclusions, finding that college-educated people to be more
    restrained than others in a wide variety of sexual behaviors.
    Ironically, poorer people are less satisfied with marital sexuality,
    (even though they report having sex somewhat more often). They are
    more likely to have extramarital relationships (at least for men,
    Argyle, 1994).

    Recent research suggests that the more short-term sexual orientation
    of poor people might be attributable to the effects of stress on the
    developing brain. Among victims of child abuse (psychological as well
    as physical), for example, early stress alters brain anatomy and
    function thereby producing a pattern of high sex drive and low sexual
    satisfaction (Teicher, et al., 2002). Considered as a complex
    stressor, poverty could have the same type of effect especially
    considering that stress is a psychological phenomenon that may be
    produced in emotionally negative homes where no threshold of criminal
    abuse is passed (Teicher, et al. 2002).

    Short-term physical relationships are not restricted to the poor, of
    course. They are conducted by affluent young people on American
    college campuses, as depicted, for example, in Townsend's (1998) study
    of sexual relationships among medical school students. His female
    informants described dozens of sexual relationships, many undertaken
    for the most trivial of motives. Some women slept with physically
    attractive men primarily to demonstrate their own sexual desirability.
    Jilted women occasionally made love with their former lover's best
    friend motivated solely by spite. Shallow, or even malicious, sexual
    relationships are clearly not restricted to poor men.

    The association between poverty and the development of relatively
    unrestricted sexual behavior of both men and women helps to explain
    why single parenthood is more common in poor neighborhoods. This
    implies adaptations of sexual psychology to varied landscapes of
    economic opportunity. In some cases, these phenomena are quite well
    understood in terms of psychological development and recent research
    has begun to pinpoint possible underlying brain mechanisms (Teicher,
    et al., 2002).

    Short-term reproductive strategies of men are quite easily
    accommodated within an evolutionary perspective because they confer
    increased reproductive success on cads, thus ensuring that a
    willingness for uncommitted sexual relationships would be promoted by
    natural selection (Symons, 1979). Why are single mothers willing to
    accept reduced paternal investment in their offspring?

    Why Women Accept Reduced Paternal Investment

    A comprehensive analysis of historical and evolutionary factors
    affecting single parenthood is not possible without some understanding
    of the dynamics of marriage markets and their influence on sexual
    behavior. This sort of analysis was pioneered by Guttentag and Secord
    (1983). Their cross-cultural and historical comparisons demonstrated
    that a scarcity of men in the population is generally correlated with
    "liberated" sexual behavior as women compete for a diminished pool of
    young men by emphasizing their sexual availability. The scarcity of
    men in ancient Sparta, due partly to the practice of male infanticide,
    and to warfare, was used to explain the sexual liberation of women
    there, for example, whereas the excess of males in contemporary Athens
    accounted for the extreme preoccupation with feminine chastity in that

    Similarly, Guttentag and Secord's (1983) historical analysis of sexual
    behavior in the U.S. concluded that a more difficult marriage market
    faced by young women in the 1960s compared to the 1950s liberated
    women's sexual behavior, as more women began having intercourse before
    marriage, and dressed provocatively suggesting sexual availability.
    Changing sexual behavior can thus be accounted for in terms of
    changing marriage market dynamics.

    A scarcity of men, means that some women will inevitably fail to marry
    and are therefore liable to become sexually active outside marriage.
    The presence of a pool of sexually active single women essentially
    sets up an "arms race" whereby women who are interested in marriage
    must offer pre-marital sexual activity to compete for masculine
    attention and affection. This is in marked contrast to the coy
    strategy prevailing in societies where women's marriage prospects are
    very good and where they advertise chastity as a means of ensuring
    paternity confidence that is universally desirable for prospective
    husbands (Barber, 2002a, Symons, 1979). In sexually liberated
    societies, women thus play a very delicate game of implying that they
    are ready for sexual intercourse with their boyfriend, while
    simultaneously denying that are the sort of woman who enjoys many sex
    partners and is thus undesirable as a wife who provides low confidence
    of paternity in relation to children of the marriage (Symons, 1979).
    Such marriage market dynamics are particularly influential in the
    lives of poor women. For them, the supply of marriageable males is
    particularly bleak, as already discussed. There is thus a large pool
    of sexually active single women in low-income neighborhoods, which
    favors a cad strategy that seems to be particularly common in that
    environment. The prevalence of short-term reproductive strategies
    means that both males and females are likely to be sexually active
    from an early age. (Indeed a women's sexual maturation can be
    accelerated by a few months by a stressful early environment such as
    that characteristic of poverty and father absence, Ellis, et al.
    2003). A plentiful supply of sexually active single young women favors
    an opportunistic strategy by young men who can achieve sexual
    gratification without providing any long term emotional commitment, or
    paternal investment (in the event of pregnancy).

    If poverty makes it difficult for men to support their children, their
    reproductive success is favored by pursuing a cad strategy (i.e.,
    seeking sexual gratification in short-term relationships) and
    emphasizing mating effort rather than paternal investment. This might
    be considered the default strategy of male mammals, most of which
    invest little in offspring and compete aggressively with other males
    for mating opportunities and reproductive success (Geary and Flinn,
    2001; Hewlett, 1992). (The word "strategy" is used here in the
    technical sense of an evolutionary mechanism, has no connotation of
    intentionality, and does not imply that people want to have children -
    only that they behave in ways that are liable to increase their
    reproductive success).

    If poor men are less able to provide economic support for their
    children, then devoting themselves to mating effort rather than
    paternal investment is adaptive, i.e., generally promotes reproductive
    success. The cad strategy may work for economically-disadvantaged men.
    The real question is why young women should forgo most paternal
    investment by opting to raise children alone.

    The reasons are complex but the following points should be borne in

    Poor women who do poorly at school, have less to lose, socially or
    economically, from early childbearing. In fact, bearing a child gives
    them a sense of importance and accomplishment that they did not get
    from their academic efforts (Barber, 2000a; Musick, 1993).

    Young mothers may anticipate a long-term relationship when they become
    sexually active.

    Fathers of children borne by teenage women are characteristically more
    than three years older than the mothers (Landry, and Forrest, 1995).
    The father's relative maturity can be flattering to younger women and
    means that he tends to be more attractive as well as more controlling.

    In addition to gravitating to older men, poor young women evidently
    prefer to associate with socially dominant men as well. Thus, gang
    leaders are much more sexually active than other gang members and have
    more sexual partners (Palmer, and Tilley, 1995). This implies that
    women living in poor urban neighborhoods select men on the basis of
    qualities associated with social success there, i.e., on the basis of
    attributes such as social dominance, ruthlessness, and aggression,
    that generally have negative connotations for women in more affluent
    neighborhoods. This suggests adaptive design because they are
    acquiring for their male offspring qualities associated with
    reproductive success in the local environment (Barber, 1995).

    The majority of poor single teen mothers have a history of some kind
    of childhood sexual abuse (Barber, 2000a; Boyer and Pine, 1992;
    Musick, 1993). This has the effect both of advancing the age of
    voluntary sexual activity and works against the development of social
    skills that would facilitate equity in their sexual relationships.

    Looking at the world from a very different perspective, social workers
    are inclined to see teenage child-bearing as both self-defeating and
    pathological, which it might be in more affluent circumstances. Yet, a
    good case can be made that early single parenthood is essentially an
    adaptive response to an environment in which there is limited economic
    opportunities for women and where they cannot expect much paternal
    investment in their children.

    In a low-investment environment, there is increased emphasis on
    physical attractiveness in the selection of a sexual partner (Buss,
    1994). When competing amongst each other for the attentions of a
    low-investing partner, women emphasize their own sexuality and also
    use sexual favors to manipulate men (Cashdan, 1993; Townsend, 1998).
    Thus, if she wishes to leave an undesirable home environment, a young
    woman may initiate a cohabiting relationship to obtain free
    accommodation (Musick, 1993). Male partners are likely to be
    physically strong and socially dominant (Palmer and Tilley, 1995).

    From the perspective of a social worker, it is difficult to see
    displays of aggressive masculinity, or promotion in a criminal
    organization, as measures of social success but poor women are
    attracted to socially dominant men for the same reason that
    middle-class women are likely to be attracted to mild-mannered
    professional men with high earning ability - these are different
    measures of social success in very different social environments. By
    being attracted to dominant men, women in poor neighborhoods acquire
    at least temporary access to resources (Buss, 1999; Cashdan, 1993).
    They also acquire the genetic basis of social success that contributes
    a competitive advantage to their children. These adaptive
    considerations are relevant to any comprehensive account of
    reproductive choices underlying single teen parenthood but they are
    unlikely to enter the lexicon of social workers.

    One of the most interesting aspects of sexual behavior in an
    economically depressed environment - one having an unusually difficult
    marriage market for women - is that many young women view motherhood
    in a very positive light and rarely as a mistake. Many look forward to
    becoming pregnant as a way of obtaining someone to love. Birth of a
    first baby may also constitute a rite of passage that provides entry
    to the world of adults and the society of other young mothers (Musick,
    1993). Their optimism in the face of formidable difficulties may be
    one of the most remarkable examples of adaptive modulation of
    psychological development to a niche of low paternal investment.

    Willingness to assume the burden of rearing children alone may stem
    from such optimism. Alternatively, it might reflect unsuitability of
    biological fathers for the social role of being a parent. Although a
    nurturant father may contribute a great deal to the happiness, health,
    and social prospects, of offspring, this argument cuts both ways and
    antisocial fathers can have the opposite effect. Indeed,
    criminologists have recently found evidence that living with a
    criminal father makes children more likely to commit serious crimes
    (Jaffee, Moffitt, Caspi, and Taylor, 2003). Women living in
    economically depressed neighborhoods might sometimes prefer to raise
    their children alone if the presence of an antisocial father increased
    the likelihood of their children getting involved in criminal
    enterprises at considerable risk to their lives and liberty.

    Interview research on poor single mothers in the U.S. finds that many
    consider teenage childbearing both acceptable and normal (Musick,
    1993). They deny the claims of social scientists that they are
    damaging their own futures, or doing a disservice to their communities
    by raising children who are at higher risk of criminality, drug
    addiction, poverty, and so forth. Motherhood provides many of these
    young women with a sense of optimism, purpose and meaning in their
    lives and allows them to hope for a better future. One of Judith
    Musick's (1993) informants articulated these sentiments clearly in a
    diary entry:

      "I Like it when people notice I'm having a baby. It gives me a good
      feeling inside and makes me feel important." "Baby will be here any
      day now and I will be a proud Teen Mom with my head held high." pp.

     While single parenthood increases, almost inevitably, with declining
    marriage prospects for women this is not the complete picture. The
    modern environment evidently creates situations in which single
    parenthood may actually be the desirable, or preferred option, even
    though such a scenario was rare, or nonexistent, throughout the
    two-million-year-plus history of our species. Before taking up that
    theme in relation to changes in family structure in Sweden, it is
    desirable to say something about "values" explanations of sexual
    behavior that remain influential among scholars.

    Values and the Single Mother

    Values interpretations of human sexual behavior rest on the notion of
    free will, i.e., that there are good and bad options that are
    voluntarily chosen by freely-acting agents. The concept of free choice
    of family structure, although widely accepted is problematic for
    scientists: if each individual was really autonomous, social
    scientists would be irrelevant in the sense that they could not
    predict human behavior.

    Even if belief in free will is largely inconsistent with scientific
    inquiry, social scientists are forced to come to terms with arguments
    that human behavior is determined by "values" that are either
    propagated passively into individuals by their social environment, or
    chosen voluntarily from an array of alternatives. They do so in at
    least three distinct ways. The first is to interpret free will as a
    popular illusion irrelevant to scientific analysis. The second is to
    write free will off as a source of noise, or unexplained error in the
    data. The third is to use it as an independent variable, or predictor.
    This can be done in various ways, including experiments that either
    encourage, or frustrate a person's sense of autonomy. In one
    well-known experiment (Lepper and Greene, 1975) children who were paid
    for drawing with felt-tipped pens lost their enthusiasm for this
    activity when payments were stopped, thereby providing evidence that
    they are governed by intrinsic motivation for some behavior that can
    be affected by providing external rewards.

    In social research, the third of these alternatives is frequently
    employed when choices are studied in the form of attitudes measured at
    an earlier point in time to see whether they are helpful in predicting
    subsequent behavior. As intimated above, this enterprise has produced
    mixed results. Evidence suggests that, sexual behavior affects sexual
    attitudes just as much as sexual attitudes affect behavior (Moors,
    2000). If attitudes and behavior are not clearly separable, they do
    not satisfy the criterion of independence between causes and effects
    that is a fundamental, assumption of scientific explanation. If
    behavioral attitudes, or self-reported choices, are to avoid
    tautology, (i.e., circularity), and provide useful scientific
    explanations of behavior, they must be truly independent of the
    behavior they are used to predict.

    Even if sexual attitudes could be separated from behavior, there are
    many reasons why individual behavior might not conform to attitudes,
    or preferences, illustrating a further weakness in values as a
    scientific construct. A person who is addicted to cigarettes may hate
    their addiction, for example, but feel powerless to stop smoking. The
    social environment often frustrates individual choices, as well, and
    this is clearly true in the case of single parenthood that may be a
    product of limited marital opportunities for young women. Thus,
    research on the attitudes to marriage of young African American women
    found that they strongly endorsed the value of marriage at a time when
    few Black women could hope to marry before having their first child.
    Moreover, exactly the same proportion of African American women as the
    rest of the population believed that it was desirable to marry before
    raising a family, although they were more than twice as likely to do
    the opposite, i.e., raise their first child outside marriage (South,

    The mismatch between family aspirations and actual reproductive
    behavior is not peculiar to African Americans, of course. Thus, the
    majority of Americans believe strongly in the permanence of marriage,
    even though there has been a sharp rise in divorce rates, and in
    numbers of cohabiting couples, who substitute an informal, often
    temporary, union for a more permanent, more binding one (Smock, 1999).
    Despite these inconsistencies, the married family remains the
    statistical norm in the sense that nine Americans out of 10 still
    marry and that the majority of children spend most of their childhood
    in married households (including step parents, Wellner, 2002).

    In many European countries, including France, where more women aged
    20-24 yr now live with their boyfriends than live with husbands,
    matters are very different (Ekert-Jaffee, and Solaz, 2001).
    Approximately 85% of French marriages begin as cohabiting
    arrangements. Sweden is an interesting country in the sense that
    single parenthood is currently the norm there. This might be a
    misleading conclusion, however, because unmarried Swedish women are
    quite likely to be living with the father of their children.

    Single Parenthood in Sweden

    Sweden is sometimes seen as the exemplar of declining marriage and
    consequently of increasing levels of single parenthood. Thus, Swedish
    marriage rates declined 40% between 1966 and 1974 alone and are
    currently at a historic low as well as being one of the world's lowest
    (Popenoe, 1988). The decline in marriage rates is attributable to a
    concurrent rise in cohabitation rates. If couples may live in the same
    home and enjoy all the benefits of marriage without a permanent
    commitment, why should they marry?

    Widespread failure to marry is not the only sign of weakness in
    Swedish marriages. Despite unusually low marriage rates, that would be
    expected to screen out many potentially incompatible marriages,
    Swedish marriages are highly unstable compared to other countries at a
    similar level of economic development. At the end of the twentieth
    century, Sweden's divorce rate, calculated as a proportion of all
    marriages, stood at 64%, second only to that of Russia where 65% of
    marriages ended in divorce (Moffett, 2002).

    By 1990, about 50% of Swedish men aged 25-29 were cohabiting. As a
    result, half of births were outside marriage (Chesnais, 1996).
    Traditional marriages are little more than a historical curiosity and
    there has been a rapid increase in the number of single young Swedes
    living alone. Thus, in downtown Stockholm just 37% of households
    contain married people. With 85% of young women with children under
    seven in the workforce, the young home maker has receded into history
    (Sweden's Splashy Women, 1996).

    Although most births are to single mothers in a technical sense, as a
    practical matter the great majority of young children live with both
    parents. It might thus appear that the transition in Swedish families
    is more a question of appearance than reality. Yet, this is not true
    because cohabiting unions dissolve much more rapidly than marriages,
    even in a country like Sweden that has an exceptionally high divorce
    rate (Popenoe, 1988). In one study of U.S. women born between 1936 and
    1960, for example, the dissolution rate for cohabiting couples with
    one child was triple that of comparable married couples (Smock, 2000)
    and a similar pattern is seen in Sweden (Popenoe, 1988).

    Although the data on single parenthood in Sweden may thus exaggerate
    the lack of commitment of fathers to their children, high ratios of
    births to single women are nevertheless correlated with a relative
    lack of commitment of parents to a permanent relationship that reduces
    the amount of time that fathers will spend living in the same home as
    their children. Why do so many Swedish couples, compared to the U.S.
    and other developed countries, avoid marrying before reproducing? The
    conventional answer to this question may be summed up in two words
    "welfare state." The Swedish state is so generous in its support of
    mothers and children that women raising children outside marriage are
    not exposed to the economic risks encountered by single mothers in the
    U.S., for example.

    A comprehensive discussion of the historical roots of the Swedish
    welfare state is outside the scope of this paper but a few points bear
    emphasis. The Swedish welfare state grew out of perceived problems of
    declining population but many of its current characteristics were
    designed to solve the conflict between careers and family faced by
    women in most developed countries (Carlson, 1990) so that more married
    women could work, thereby boosting the Swedish economy. The Swedish
    solution to this conflict was to nationalize many of the economic
    functions of the traditional family so that it was easier for Swedish
    women to raise children without economic cooperation from husbands.

    Tax reforms of the 1970s also increased the financial incentive for
    women to work, and reduced their economic dependence on husbands.
    Thus, high tax rates for jointly-filing married couples were
    eliminated and married people were taxed separately (Carlson, 1990).
    Married women's earnings were no longer vulnerable to the high tax
    rates that had seriously undermined the benefits of a second household
    income to the extent of discouraging married women from going to work
    at all.

    Such changes in the tax code, as well as providing daycare
    entitlements for mothers, were successful at increasing female labor
    participation. By 1995, 85% of Swedish women worked outside the home,
    the highest participation seen in any industrialized country and twice
    the labor force participation of Italian women, for instance. Many
    (40%) worked part-time, however, thus limiting potential conflicts
    between career and family (Home Sweet Home, 1995).

    Despite working part time, Swedish women do not lose occupational
    prestige as a consequence. Gender equality is vigorously promoted and
    women enjoy equal status with men in most occupations (Sweden's
    Splashy Women, 1996). This is certainly true of politics. After the
    1994 election, women held 41% of the seats in the Riksdag, the highest
    proportion of female political representation in any country, and
    considerably higher than the 14% of women in the U.S. House of
    Representatives and in the Senate (as of 2003). Half of the cabinet
    members (11 of 22) were also women. (Academic life evidently lags
    other fields in regard to gender equality. Thus, Swedish females must
    publish twice as much as Swedish males to earn a fellowship in
    medicine, for example, Wenneras and Wold, 1997).

    Direct government support of Swedish children is generous. Free school
    meals, and clothing, and good childcare benefits, mean that no mother
    is dependent on her husband, or lover, for economic necessities for
    herself or her children. A man's decision to leave his children does
    not send the family on a downward spiral into hardship, or poverty, as
    it does in most other countries. Aggressive enforcement of child
    support laws also mean that a father's presence in the home is not
    necessary to ensure his financial contribution to children. As a
    result of these radical family policies, very few Swedish children
    live in poverty. In 1990, only 7% of children lived in households with
    an income under 50% of the national average. In other words, 93% of
    children lived in comparative affluence (Home Sweet Home, 1995).

    Conservative scholars have criticized the Swedish welfare state for
    weakening married families by taking over many of the economic
    functions previously fulfilled by fathers (Popenoe, 1988). Expansion
    of the welfare state has indeed been accompanied by a rapid, and
    historically unprecedented, increase in births outside wedlock, from
    11% in 1960 to 53% in 1995 (Home Sweet Home, 1995). Although 19 out of
    20 babies begin life under the same roof as their fathers most will
    not reach maturity without experiencing parental separation.

    Although Sweden has a very high ratio of children born to single
    mothers, this does not have the same implications for children as it
    would in many other countries. In addition to being materially
    provided for, most Swedish children also spend the formative early
    years of life in two-parent families. It is not too surprising that
    children of single parents in Sweden turn out very much as children of
    married couples do in other countries given that domestic arrangements
    are quite similar despite the lack of a formal marriage contract.

    In particular, Sweden does not have the social problems associated
    with single parenthood among poor women in many other developed
    countries. Birth rates to teenage women are very low, for example at
    1% annually compared to 6% in the U.S. (Population Reference Bureau,
    1998). This is all the more remarkable given that women are sexually
    active from a comparatively early age (Carlson, 1990; Popenoe, 1988;
    Weinberg, Lottes, and Shaver, 1995). The main reason for avoiding
    unplanned pregnancies may be the widespread use of contraceptives that
    are easily available and promoted by many years of public education in
    responsible sexuality.

    Other factors matter also. One important factor underlying low rates
    of single teenage childbearing is the fact that Swedish women have
    unusually good career prospects. They are thus motivated to delay
    having a family until they are established in careers (see Goldin,

    It is interesting that Sweden has low rates of serious crime despite
    its high rates of single parenthood and the presence of a substantial
    immigrant population. Other countries with high ratios of single
    parenthood often have high crime rates because so many children are
    born in high-risk groups, specifically to poor single mothers. In
    Sweden many of the births to nominally single parents are to mature
    affluent women, and few are to poor teenagers. Considering each of
    these factors, it is perhaps unsurprising that Sweden has much lower
    rates of serious crime than would be predicted by the ratio of births
    to single women. Compared to violent crime rates in the U.S., for
    example, Sweden has ten times fewer assaults, two-and-a-half times
    fewer rapes, and about 25% fewer murders. based on INTERPOL (1990)

    The fact that the Swedish family system does not produce high rates of
    crime or other social problems, suggests that single parenthood may be
    less important than poverty in determining the social problems
    associated with high nonmarital birth ratios in other countries. This
    is a risky assumption for at least two reasons however. The first is
    that Swedish children generally do live with their fathers in the
    early years of life when the brain is particularly responsive both to
    stressors and environmental impoverishment. The second is that the
    increased stress in children's lives attributable to father absence,
    as measured in terms of stress hormones (Flinn, 1999), may be more
    pronounced in poor homes for various reasons. Thus, poverty is a
    complex stressor and any kind of social support, particularly that
    from co-residing fathers, could mitigate its effects on behavioral
    development. As well as experiencing less stress due to their social
    environment and living arrangements, children of affluent single
    mothers may benefit from have more extensive social support networks.

    So far as the evolutionarily-relevant aspects of the early environment
    are concerned, being raised by a single mother in Sweden is evidently
    not very different from being raised by married parents in other
    countries. Having come to the end of this summary of data on single
    parenthood from an ESS perspective, it is time to ask what this
    perspective contributes to the problem that is new or worthwhile.

    ESS: Of What Value for Research on Single Parenthood

    The data on single parenthood suggest that ESS provides the kind of
    large framework into which many kinds of evidence can be assimilated.
    Thus, the response of single parenthood ratios to similar influences
    across time and from one society to another is consistent with ESS
    (assumption 3) but not with most other perspectives in the social
    sciences. Moreover, there is little convincing evidence in support of
    top-down values interpretations of societal variation and very good
    evidence that such differences are mediated directly through
    environmental influences on individuals (assumption 2). The most
    important of such influences include the marriage market, and the
    economic prospects of single women as compared to the overall
    well-being of children in two-parent families.

    Perhaps the most interesting aspect of the application of ESS to
    single parenthood is the fact that sexual psychology of young women
    and men varies predictably both as a function of the immediate social
    environment, and as a function of the developmental social environment
    (assumption 4). The most important aspect of such variation is
    arguably the potential for paternal investment in children, as well as
    the extent to which women are economically independent of such
    investment (a circumstance that prevails in Sweden due to the
    provisions of the welfare state) and in many economically developed
    countries due to expanded professional opportunities for women.

    A diminished capacity for paternal investment is characteristic of
    poverty in modern societies, helping to account for variation in
    sexual behavior, and single parenthood ratios, as a function of
    income. Moreover, research on brain development points to
    psychological stress as a possible mediator in the ontogeny of
    differing patterns of sexual behavior as a function of parental
    income. Presumably, this example of evolved developmental plasticity
    would have tracked very different stressors in the evolutionary past,
    perhaps a scarcity of food rather than the modern stimulus of
    insufficient monetary resources.

    Scientific theories perform two essential functions. They organize
    information and allow it to be stored in an orderly fashion, rather
    like the ordered arrangement of merchandise in a warehouse. Large
    scale theories, like ESS can be though of as providing a great deal of
    space where new information can be deposited. In addition to the role
    of organizing information, they stimulate research. This is analogous
    to the owner of a warehouse finding that a bay of the warehouse is
    empty and sending out to the supplier for the missing item. (In this
    case, of course, the role of supplier is performed by researchers and
    scientific knowledge is steadily accumulated instead of ebbing and
    flowing as in a real warehouse).

    This paper demonstrates that ESS can accommodate a great deal of
    information in an orderly fashion. As far as the function of
    stimulating research is concerned, it should be obvious that the data
    reviewed here merely scratches the surface of potential research
    projects in this field. Even so, ESS offers the prospect of revealing
    new phenomena or helping us to see established facts in a new light.
    Thus, the persistence of young single parenthood in economically
    distressed circumstances that is often dismissed as a pathological
    phenomenon should probably be seen as an adaptive response to a
    developmental environment characterized by reduced paternal
    investment. In any case, social workers who fail to make this
    connection are (as they currently accept) singularly unlikely to
    succeed in producing behavioral changes. The success of ESS in
    reconciling many different types of data offers hope that it may do
    the same for other content areas. One limitation on this conclusion is
    that most of the data come from economically developed countries where
    monogamy is the norm. If anthropologists were to apply this approach
    to subsistence societies, where marriage systems are different, there
    is no guarantee that they would draw similar conclusions. On the other
    hand, the fact that this approach works for modern societies means
    that it passes a more severe test given that our behavior has diverged
    more from subsistence ancestors.

    In summary, a few simple evolutionary concepts help to explain a great
    deal of the variation in single parenthood across time, countries,
    ethnic groups, and economic classes. This supports the view that the
    concept of adaptation can be applied to modern societies, even those
    that have passed through the demographic shift. Doing so not only
    provides a heuristically useful means of drawing together a great deal
    of information from many disciplines (including evolutionary biology,
    anthropology, history, health, sociology, psychology, and economics
    among others) but offers the prospect of a social science that
    transcends disciplinary boundaries and may provide universal
    explanations for social behavior that can be applied at any time,
    place, or historical context, thus satisfying the basic scientific
    criterion of universality of explanation and evading the pitfalls of
    cultural relativism.

    A reviewer of this paper complained that the assumptions of ESS are
    not new and this is arguably true if they are taken piecemeal. The
    focus of the new research strategy is not on any individual
    assumption, however, but on what they can accomplish if applied
    simultaneously, something that has not been previously attempted. In
    particular, ESS aims to unite the time scales of evolutionary
    psychology and the social sciences. The data on single parenthood
    demonstrate that this new approach offers a credible method for
    uniting evolutionary psychology and the social sciences, a problem
    that has perplexed scholars in these fields for many years (Barkow,
    Cosmides, and Tooby, 1992).

    Received 9 March, 2004, Revision received 31 March, 2005, Accepted 29
    April, 2005.


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Nigel Barber: mailto:nbarber at ime.net

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