Attachment theory (e.g., Bowlby Reference Bowlby1969/1982) has been used so widely in research and practice that it is easy to forget its theoretical roots in control systems, ethology, and the development of behavior within an evolutionary context. Del Giudice correctly directs attention on a neglected component of this theory: human reproductive strategies. Although attachment, caregiving, and sex have historically been argued to be three independent systems (e.g., Ainsworth Reference Ainsworth1989), this suggestion seems based on comparative data on the behavioral manifestations of mate attraction and the sexual response. Sex is a behavior that happens within romantic relationships; for example, Davis et al. (Reference Davis, Shaver and Vernon2004) portray sex as a behavior that serves attachment needs (see also Butzer & Campbell Reference Butzer and Campbell2008). But the evolutionary context of relationships involves a combination of these three systems (see Mikulincer Reference Mikulincer, Mikulincer and Goodman2006), and Del Giudice's proposal that sex differences in attachment have adaptive significance places an emphasis on this very issue. That is, attachment processes are an essential component and are thus reflected in sexual relationships, which follows on the respective work of Belsky (Reference Belsky2007; Belsky et al. Reference Belsky, Steinberg and Draper1991) and others (e.g., Brumbaugh & Fraley Reference Brumbaugh, Fraley, Mikulincer and Goodman2006; Chisholm Reference Chisholm1999).

Del Giudice encourages an essential expansion of the evolutionary elements of attachment because adaptive significance includes infant survival, sexual relationships, and, then, parenting commitment to the young in the next generation. In general, attachment research has focused primarily on the first and last of these three components; but what Del Giudice refers to as the “double life” of the attachment system through care-eliciting and pair-bonding needs to expand on the reproductive strategy component. This should be particularly true in adolescence, when sex is a dominant focus of attention, teens typically have a series of sexual partners, and risky sexual behavior poses health risks that have immediate and long-term consequences for reproductive life history strategies. Three points are made in this commentary: (1) that sexual behavior needs to be examined within the attachment context of sexual relationships; (2) that this seems particularly true within adolescence, when sex is a dominant theme and goal; and (3) that sex differences need to be examined as differences in correlation patterns in addition to main effects models.

Research on adult romantic attachment addresses intimacy, dependency, and trust issues within “emotionally intimate relationships” (Bartholomew & Horowitz Reference Bartholomew and Horowitz1991; Hazan & Shaver Reference Hazan and Shaver1987; for review, see Hazan et al. Reference Hazan, Campa, Gur-Yaish, Mikulincer and Goodman2006), which is related to some aspects of sexual behavior (see Brennan et al. Reference Brennan, Clark, Shaver, Simpson and Rholes1998; Davis et al. Reference Davis, Shaver and Vernon2004; Milkulincer & Goodman 2006). However, romantic attachment is not necessarily synonymous with sexual relationships. While romantic relationships usually contain a sexual element, not all sexual relationships are romantic ones (e.g., sex between friends, one-night stands), nor are all romantic relationships perceived as such after they have ended. Attachment insecurity may manifest itself in promiscuity, using sex to maintain a relationship, sexual coercion, and separation of sex from emotional caring for a partner, but these are domain-specific behaviors and motivations within sexual relationships (reviewed in Feeney & Noller Reference Feeney, Noller, Harvey, Wenzel and Sprecher2004). As noted by Belsky (Reference Belsky2007), these vary from opportunistic advantage-taking approaches to sex (i.e., avoidant) to dependent helper-at-nest kinds of approaches (e.g., ambivalent/ preoccupied). When attachment-relevant self-report items focus on behavior with sexual partners, there is the potential to predict strategic sexual behavior above and beyond that predicted by romantic relationships (see Szielasko et al. Reference Szielasko, Symons and Price2007; under review).

This distinction between sexual and romantic partners may be particularly relevant to teens who are very interested in sex, typically have a series of sexual partners during adolescence and early adulthood, and may be more motivated by physical attraction than an evaluation of partners in terms of future co-parenting investment. Del Giudice frames this issue within life history theory when he distinguishes between mating effort and parenting effort, wherein teens are usually invested in the former and not the latter. Downward extensions of adult-oriented attachment measures (e.g., Allen & Land Reference Allen, Land, Cassidy and Shaver1999; O'Connor & Byrne Reference O'Connor and Byrne2007) may mask the significance that sexual behavior and misbehavior have with regard to later relationships and developmental processes for late teens (see Feeney et al. Reference Feeney, Noller and Patty1993; Kobak et al. Reference Kobak, Rosenthal, Zajac and Madsen2007). Keep in mind that human evolution took place over a time frame when pregnancy was not controllable, so adolescence is the developmental period when pregnancies historically arose, not adulthood, when current-day pregnancies are often fit in with other life history strategies of investment.

Del Giudice addresses sex differences in attachment, but most of the literature reviewed uses a main effects model of sex that describes avoidant males and ambivalent/dependent females (i.e., investment-eliciting). Although these patterns fit his theory, no doubt there are avoidant females and preoccupied males whose sexual adaptations must also be considered. If ambivalence is related to sexual coercion and avoidance related to promiscuity (see Bartholomew & Allison Reference Bartholomew, Allison, Mikulincer and Goodman2006; Feeney & Noller, Reference Feeney, Noller, Harvey, Wenzel and Sprecher2004; Szielasko et al. Reference Szielasko, Symons and Price2007), for example, it would be important to know whether this is equally true for both males and females, and how coercive behavior may vary between the sexes when a relationship feels threatened (e.g., physical force? trickery?). Such a finding would not necessarily pose a problem for the proposed theory, as ultimately attachment styles reflect adaptations to environmental circumstances, but we argue for a need to address potentially different patterns of correlations between attachment constructs and sexual behavior/misbehavior in males and females.

Del Giudice hints at this when discussing different implications of insecurity for the reproductive strategies of men and women, but he could go even further with this thinking. Literature suggests that avoidance is related to a greater number of less committed sexual relationships, and ambivalence is related to dependency and possessiveness, but is this equally true for both genders, or are there sex-specific manifestations of sexual behavior that reflect these attachment styles? And may these behaviors have different longitudinal consequences for personality development and attachment styles?

Bowlby (Reference Bowlby1969/1982) wrote that it may be that “attachment and sexual behavior share certain components and causal mechanisms” (p. 233), and considering the adaptive significance of both within the context of adult relationships is essential. This article by Del Giudice promises to invigorate thinking on this component of attachment theory in an evolutionary context, building on the inspiration of Belsky et al. (Reference Belsky, Steinberg and Draper1991) that took place almost two decades ago.