People who live the fast life act in ways that increase short-term reproductive gains (e.g., risk-taking, impulsivity, early sexual maturation, and high mating effort). They also tend to show high levels of insecure attachment as adults, which influences many areas of their social lives, including interactions with friends and colleagues, as well as romantic partners. The development of attachment styles in those who live the fast life has received a lot of research interest recently by evolutionary theorists who are shedding light on longstanding issues in child development.

Attachment Styles and Reproduction

John Bowlby's (1969) attachment theory revolutionized developmental psychology and our understanding of parent-child relationships. As brilliant as his theory was, he was missing one crucial component. Focusing entirely on the role of attachment for survival, he completely ignored the roles the attachment system plays in reproduction. This is understandable, since Bowlby focused on infant attachment, and obviously infants aren't interested in reproducing. The game changes, however, once we start looking at stages of development that involve the struggle for reproduction.


Modern evolutionary psychologists, building on Bowlby's important work but incorporating Darwinian principles of sexual selection, conceptualize the attachment system as evolving for two related but distinct adaptive reasons: survival and reproduction. Certainly, adult attachment styles serve a different function than childhood attachment styles. In children, attachment styles help elicit care from parents in order to survive whereas in adults, attachment styles serve to maintain long-term pair-bonds that can increase reproductive success.

Still, there is an emerging consensus among neurobiologists and social-personality psychologists that both parent-infant bonds and long-term couple relationships draw on the same attachment motivational system (Del Giudice & Belsky, 2010). The behavioral and psychological displays of adult bond formation, separation, and loss show striking similarities with the same displays in children (Feeney, 1999) and neurobiological studies also show substantial overlap in the neurochemical and neuroanatomical substrates involved in both types of relationships (e.g., Pedersen et al., 2005).

While other drives surely come into play in adult relations (e.g., sexual attraction), the evidence suggests that the motivational system that underlies parent-infant bonds may have been at least partially co-opted during the course of human evolution to promote long-term bonding in an adult context. The attachment system is closely linked to the stress response system and helps regulate a child's feelings of distress, pain, fear, and loneliness.

Adopting an evolutionary approach, Belsky et al. (1991) and Chisholm (1993) argue that children in the first years of their lives assess their levels of attachment security and use those cues to assess how risky and uncertain their environments are (see Part II, Developing a Life History Strategy). This assessment has a drastic effect on the formation of a person's reproductive strategies and whether he or she will live a fast or slower life. 

Children raised in harsh and unpredictable environments who are also biologically prepared to live the fast life will tend to develop an insecure attachment style, whereas those growing up in safe and secure environments biologically prepared to live a slower life will tend to develop secure attachment styles. 


Insecure

 children are likely to follow a fast life trajectory, involving early reproduction and physical maturation, short-term, uncommitted relationships with partners, low parental investment, and increased opportunism and risk-taking. Insecurely attached adults do report shorter estimates of their own life expectancy (Chisholm, 1999), so there does appear to be a link between adult attachment security and perceptions of the harshness of the environmentSecure children, on the other hand, are predicted to follow reproductive strategies involving later reproduction, higher parental investment, longer-term couple relationships, and more trusting, mutually beneficial close personal relationships in all aspects of their lives. 

These models also predict the specific aspects of the family environment that act as cues of security to the child. These aspects involve family stress, harmonious parent-child relations, father absence, and marital conflict. Belsky et al. (1991) proposed that rejected or insensitive parenting conveys information about the lack and unpredictability of resources, the low trust and cooperation of people in the environment, and the instability and low commitment in couple relationships (see Part II, Developing a Life History Strategy).

A key assumption in developmental psychology is that humans go through various stages in their development, each stage associated with milestones. What are the important stages in the development of attachment?

Stages of Attachment

Marco Del Giudice, a young, rising superstar in evolutionary psychology, in only the past few years has published a flurry of papers (see References section) relating to the development of the adult attachment system. Building on the work of Belsky et al. (1991) and Chisholm (1999), Del Giudice has shed much light on the developmental time course leading from infant attachment styles to mature, sexually differentiated strategies.

Del Giudice proposes that life history strategies develop in a flexible, multi-stage fashion. According to this view, life history strategies remain open to continual modification depending on life stage and context (although some people may be more flexibly adaptive than others; see Part II, Developing a Life History Strategy). Del Giudice also proposes that throughout human development there are developmental switch points where an individual's genes are calibrated with information from the environment and this integration then shapes an individual's choice of life history strategy (also see West-Eberhard, 2003).

What are these switch points?


While strategy-setting may occur even before birth (exposure to maternal stress hormones), Del Giudice and his colleagues argue that  the passage from early to middle childhood is the first crucial switch point (Del Giudice, Angeleri, & Manera, 2009). During this hormonally mediated turning point, environmental and genetic factors are integrated to redirect the individual’s reproductive strategy in a sexually differentiated way and this neurobiological "switching" mechanism is strongly tied to adrenarche.

Adrenarche is an endocrine maturational event also known as "adrenal puberty" (e.g., Auchus & Rainey, 2004). At about 5-8 years of age, the adrenal glands of both sexes begin increasing output of adrenal androgens. These andogens don't have much effect on physical development but can directly influence psychological functioning directly through neuromodulatory effects, and can indirectly influence psychological functioning in the brain through hormones such as testosterone and/or estrogen in the brain (e.g., Adkins-Regan, 2005; Del Giudice & Belsky, 2010). Research does show that bad parenting on both the mother and the father's part and higher marital discord during early childhood predicts earlier emergence of adrenarche in boys and girls in first grade, and the beginning stages of puberty in girls in fifth grade (ages 10-11; see Ellis & Essex, 2007). 

While still quite speculative, Del Giudice (2009) offer a psychobiological model of the effects of adrenarche on the development of life history strategy (see Campbell, 2006 for an alternative perspective). Del Giudice argues that around the age of 7 (the equivalent of primate juvenility, see Geary, 1998), this psychobiological process comes online and enables the child to function in a sex-differentiated world. 

What's going on at this age that is so sex-differentiated? It is during this stage of development where competition for social status in their peer group and dominance-related play intensifies. This is an important sex-differentiated stage of development for children and they are just beginning to establish their identities and social roles, with long-lasting consequences for development. As a result, there is heightened same-sex competition for status (Del Giudice & Belsky, 2010).

The next major switch point is puberty, when individuals first enter the arena of actual mating and reproduction (Del Guidice & Belsky, 2010). Several studies show that stressful and negative family relationships do seem to accelerate the onset of puberty (note: mostly in females; see Belsky et al., 2007; Tither & Ellis, 2008 for reviews). The function of attachment also changes dramatically during puberty, from survival to regulating long-term bonding between reproductive partners.

Other switch points can be found across the human life course. Menopause is a major one for women, and men around the world also increase their parental effort when approaching middle age (Winking et al., 2007). The birth of one's child may also be a developmental switch point. It signals reproductive success and affects hormonal functioning in both sexes (Storey et al., 2000).

A fascinating implication of the sex-differentiation during these developmental switch points is that sex differences in attachment styles may emerge.

Sex Differences in Attachment

Del Giudice makes the case that neither Belsky et al. (1991) or Chisholm (1999) adequately addressed the fact that males and females face different reproductive trade-offs. The payoffs of high mating effort is much larger for males, who can sire many offspring in a short amount of time. Women, on the other hand, can only have one child at a time and benefit less than men from short-term sexual encounters. The differing reproductive trade-offs men and women face is an explanation for why we find at a group level that males on average tend to live the fast life whereas females on average tend to live the slower life. What does evolutionary logic predict in terms of sex differences in particular styles of attachment?

From an evolutionary perspective, no sex differences would be expected in a secure attachment style. Secure, slow life men and women will face the same trade-offs, since they are both in it for the long haul. Del Giudice argues that sex differences in insecure attachment styles should be expected, however, and should only begin to emerge around the time when sex-differentiation comes online. According to Del Giudice, Bowlby found no sex differences in attachment styles in infants for one crucial fact: Infants aren't facing mating trade-offs.

But here is where things get more interesting. There is more than one type of insecure attachment. Insecure attachment styles vary along two related but partially separate dimensions, anxious and avoidant (Brennan, Clark, & Shaver, 1998).

Those with an anxious attachment style tend to increase their signaling of need and distress, show a constant preoccupation with the presence and availability of attachment figures, and tend to be clingy (Del Giudice & Belsky, 2010). An anxious attachment style predicts a mix of impulsive sexual attitudes, early age of intercourse (mostly for women), and intense desire for intimate, committed relationships. Anxious adults show higher dependency and are powerfully motivated to search for exclusive, intimate relationships. 


Those with

an avoidant attachment style tend to show higher levels of self-reliance, a reduced signaling of need for others, and a distancing, detached attitude toward parents or partners. In children, avoidance is related to aggression, antisocial behaviors, and inflated self-esteem. In adults, avoidance is related to low commitment in romantic relationships, avoidance of intimacy, higher levels of sexual coercion and a more promiscuous, sexually unrestrained orientation (Belsky, 1997). Avoidant attachment bears the hallmark of a low-parenting strategy, favoring short-term relationships over intimate, long-term bonding. 

Since males have less at stake, reproductively speaking, it is predicted that fast life males living under conditions of high environmental stress will show higher levels of avoidance than females, which is part of a low-investment, low commitment strategy (Del Giudice, 2009). Anxiety, on the other hand, may be a way for females living the fast life to secure and extract investment from both family members and sexual partners. These differences, however, should only emerge at key points in development that are related to sexual development. In support of this prediction, research does show that insecure attachment in juvenility predicts the early appearance of flirting and sexual contacts, even in pre-pubertal children (Sroufe et al., 1993).

To succeed in mating, an organism needs to out compete same-sex rivals and attract members of the opposite sex. For males, this involves status seeking displays of dominance and aggression and investment in traits and displays that are attractive in short-term mates, such as humor, intelligence, and creativity (Kaufman, Kozbelt, Bromley, & Miller, 2008). For females, this may involve relatively more investment in forming alliances, increasing displays of physical attractiveness, and becoming popular. 

Therefore, different style of insecure attachment may be conducive to social status depending on one's sex. Since avoidant attachment is related to traits such as aggression and inflated self-esteem, it may be part of a status-seeking strategy for young insecure males living the fast life. Such a strategy would center on mating effort, early reproduction, and selfish risk taking. For girls, dependent and closeness-oriented behaviors may be advantageous in female group relationships. Some researchers have suggested that anxious attachment in girls may relate to relational and indirect aggression, which makes evolutionary sense in the context of female peer competition. This hypothesis hasn't been directly tested yet, however.

According to this theory the mechanisms regulating strategic variation are sex differentiated and the same cues may exert quite different effects depending on the person's sex. A key environmental variable that affects this sex difference is the level of stress and risk in the environment. At moderate levels of risk, it is predicted that insecure males (but not females) should adopt short-term strategies but under high levels of risk it is more evolutionarily adaptive for both males and females to adopt a short-term mating, low-parenting strategy.

The implications here are huge, not just for attachment but also our understanding of sex differences in sexuality, dominance seeking, aggression, trust, cooperation, and risk taking. There are also implications for finding the best match. 

Which pairs work best?

In general, there are a wide range of costs and benefits for any reproductive strategy. Spending so much effort on short-term mating may limit chances for long-term, meaningful relationships (or it's possible it can help you build up important mating skills which you can then use later in a long-term relationship). A person living the fast life may have limited opportunities for initiating a potentially long-term relationship with someone who is looking for that kind of relationship. Of course, many living the fast life are just fine with short-term mating. On the other hand, the person who lives the slower life may miss out on short-term mating opportunities and may end up with less sexual variety.

Various recent threads of research (Olderbak & Figueredo, in preparation; Olderbak & Figueredo, 2010) suggests that like does tend to go with like when it comes to life history strategy- there is assortative mating on life history traits. In general, those living the fast life tend to mate with those living the fast life and those living a slower life tend to mate with those living the slower life. Although life history strategy predicts relationship satisfaction, the influence of life history strategy seems to decrease over the duration of the relationship, where other variables become more important. Clearly, life history strategy isn't everything when it comes to relationships, nor should it be. Still, it's important.

But what pairs go well together when it comes to attachment? It's unsurprising that securely attached people tend to go well together (Kirkpatrick & Davis, 1994). But what happens when we look at insecurely attached people? Do avoidant men and anxious women go well together in relationships?


Shockingly (even to the researchers), they may. Even though relationships between an avoidant man and an anxious women tend to get off to a rocky start, these kind of relationships do tend to be surprisingly stable over 3 years (Kirkpatrick & Davis, 1994). This pairing seems to a do a better job predicting relationship satisfaction than anxious-anxious or avoidant-avoidant pairings (which are very rare pairings). I think this picture of the detached, avoidant, "cool" James Dean and the anxiously attached Marilyne Monroe perfectly captures this research finding.

Del Giudice's theory of sex differences in attachment are certainly provocative, but does the evidence support the theory?

Evidence

Early studies on infants and young children did not find any sex differences in avoidance or anxiety (e.g., van Ijzendoorn, 2000). While studies of children as old as six years old usually don't find sex differences in attachment, nearly all of the available studies of children aged 7–11 that presented separate statistics by sex showed remarkable sex-biased distributions of insecure styles (Corby, 2006; Del Giudice, 2008; Del Giudice & Angeleri, 2009; Finnegan et al., 1996; Granot & Mayseless, 2001; Karavasilis, Doyle, & Markiewicz, 2003; but see Kerns, Abraham, Schlegelmilch, & Morgan, 2007 and Bakermans-Kranenburg & van IJzendoorn, 2009 for exceptions). 

A recent recent meta-analysis including 10 studies of children aged 6–14 years, using  a variety of methodologies (separation–reunion tasks, doll-play narratives, and interviews), found higher levels of an avoidant attachment style in males than females, but these differences were only found when using doll-play tasks (Bakermans-Kranenburg & van IJzendoorn, 2009). While Bakermans and van IJzendoorn interpret this as a failure to find reliable sex differences in this age group, Del Giudice & Belsky (2010) argue that Bakermans-Kranenburg and van IZndoorn's (2009) analysis did not include questionnaire studies, which always reveal large sex differences (Corby, 2006; Del Giudice & Angeleri, 2009; Finnegan et al., 1996). Del Giudice & Belsky (2010) also argue that the researchers did not properly design their study to test the evolutionary theory.

Research on adult romantic attachment reveals the presence of sex differences, with men reporting greater avoidance and/or less anxiety than women. For instance, Schmitt et al. (2003) conducted a cross-cultural study across 62 cultural regions (17,804 participants)  and found a sex difference in favor of men for avoidant attachment (D= .18). Schmitt et al. (2003) also found considerable differences across geographic regions and even within each region. The differences were predicted by measures of ecological stress: in countries with higher mortality and fertility (contexts favoring the fast life) there were higher rates of an avoidant attachment style for both sexes and a reduction of sex differences in avoidance (an effect driven by increased avoidance in women).

More recently, Del Guidice (under review) analyzed the combined results of 113 samples (66,132 participants) on romantic attachment from various countries. Overall, males showed higher levels of an avoidance attachment style and lower levels of an anxiety attachment style than females. Sex differences in anxiety peaked in young adulthood, whereas an avoidant attachment style increased through the life course. 

Interestingly, the effects were stronger for studies based on community samples as opposed to studies based on college-student samples most composed of psychology students. This is important because it suggests that the nature of college samples may restrict the magnitude of sex differences in adult romantic attachment in the general population. Virtually no sex differences were found in studies based on web surveys (which Del Guidice attributes to self-selection bias in Web participants).

Del Guidice also found that sex differences in romantic attachment differed depending on country. Sex differences were largest in western and southern Europe (D= .33 and .34, respectively), followed by the Middle East (D= .28), East Asia (D= .26), and Oceania (D=.24). The smallest differences were found in North America (D=.10). Del Guidice notes that the small differences found in North American may be due to a high proportion of college samples coming from that region. Consistent with this idea, when he looked just at North American community samples, the effect size (.26) was higher.

Criticisms

The application of attachment theory to studying adult close relationships has generated an impressive amount of theories and empirical results. The common assumption of the field has been that sex differences do not exist, and indeed hundreds of studies do show that when looking at parent-infant attachment patterns, there are no sex differences (e.g., van IJzendoorn, 2000). 

Modern evolutionary psychologists are casting this research in a different light though, concepualizing romantic attachment styles as reflecting alternative mating strategies (Jackson & Kirkpatrick, 2007; Del Giudice & Angeleri, 2010). The evolutionary predictions are specific, nuanced, and exciting, and show a lot of potential for us to come to a deeper understanding of the development of attachment across the lifespan. 

Del Giudice's (2009) theory is still tentative, and requires further testing. Nonetheless, his theory specifies the form that research should take. According to his model, research assessing sex differences in attachment shouldn't  just focus on age, but instead should look specifically at developmental stage, with the main milestone being the emergence of adrenarche. Therefore, future meta-analyses of studies of 6 to 14 year olds might fail to find sex differences in attachment if children aren't differentiated by their stage of sexual maturation.

Del Giudice's model also suggests that prior research may have underestimated the magnitude of sex differences because it lumped together those living the fast life with those living the slower life. As I already mentioned, Del Giudice's model specifically predicts that there will be no sex differences in slower life strategists who are securely attached. To really find the effect, you must zoom in on the insecurely attached folks living the fast life. Future research testing the theory should do this zooming in. Del Giudice's theory (and data) also predicts that sex differences may depend on the choice of participants (college students, mostly psych students) since community studies that show a larger cross-section of the human population do show larger differences. To add in another consideration, Del Giudice's theory suggests that researchers would benefit at looking at the amount of stress and risk in the environment, since sex differences in attachment may also differ depending on the level of harshness and unpredictability in the environment.

The literature on sex differences in attachment is currently going through a very active and fruitful emergence of new data and debate. If you want to really dig deep into the debate, I highly recommend you check out Del Giudice's target article in the journal Behavioral and Brain Sciences, along with commentaries by leading researchers, and his response to the commentaries. You can download all that here.

I do think modern evolutionary theorizing holds a lot of promise. A major concern of the critics is whether the sex difference effects are large enough to be meaningful. This is an important criticism, which only future research will settle. As just mentioned, there are many reasons why the sex difference effects reported in the literature have been underestimated. Future researchers investigating these issues would be advised to take Del Giudice's predictions into consideration in designing future studies. At the end of the day I agree with Del Giudice and Belsky (2010) when they say that

"Rather than concluding that there are no such reliable differences in middle childhood, it remains our considered opinion that not only does theory suggest that these should emerge and evidence indicate that they can be detected, but that embracing the null is, for the time being, premature and perhaps even counterproductive."

Toward a Developmental Evolutionary Psychology

Evolutionary biology is addressing issues central to child development, such as plasticity and genotype-environment interactions (Belsky, 1997, 2005; Belsky & Pluess, 2009; Boyce & Ellis, 2005; Wolf, van Doorn, & Weissing, 2008). The study of organismic development is even becoming a major foundation of the new theoretical synthesis in evolution (see Del Giudice & Belsky, 2010; West-Eberhard, 2003).

The field of developmental evolutionary psychology has a lot of promise to shed light on data that may not have made sense before, such as why attachment patterns correlate with such a wide range of developmental outcomes as aggression, sexuality, cooperation, and psychopathology (Cassidy & Shaver, 2008).

In order to test the novel predictions being made by evolutionary psychologists, researchers will have to integrate different levels of analysis through an interdisciplinary approach. Hopefully by doing so, we can come to a deeper understanding of the potentially different mental states, trade-offs, attachment styles, and development of men and women living the fast and slower life.

© 2010 by Scott Barry Kaufman

Other Parts of the Series

Part I: Evolution of the Fast Life

Part II: Developing a Fast Life History Strategy

Part IV, Rebelliousness, Risk, Social Deviance, and Educational Policy

Part V, Social Class and Public Policy

Part VI: Consilience, Pop Culture, and Modern Living

References

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