Del Giudice's evolutionary model integrating attachment with human reproductive strategies contributes to our understanding of the adaptive significance of gender differences in attachment, and of the role of sex-related endocrine mechanisms on development of attachment styles. He argues that gender differences in attachment patterns emerge during middle childhood, and specifically, that insecure girls tend to develop ambivalent attachment, whereas insecure boys develop avoidant attachment, when faced with new social demands driven by the peer group.

If this argument is correct, we should expect that insecure girls, similar to boys, would be more likely to shift to avoidant attachment in middle childhood. Thus, this commentary cites evidence supporting why this shift to avoidant attachment is essential. We follow Del Giudice's logic in analyzing the emergence of aggression as a correlate of avoidant attachment in girls at this stage of childhood.

According to Del Giudice's analysis of attachment styles in middle childhood, insecure children without a secure family environment must “begin to fight their way through social reality” (target article, sect. 7.1.2). Therefore, insecure girls are more likely to shift to avoidant styles than ambivalent styles,Footnote ¹ which emerge from competition in the peer group. The behavioral correlates of avoidant attachment (i.e., aggression) are already selected at this stage because they are more adaptive than traits associated with ambivalent attachment (e.g., dependency, behavioral immaturity, and passivity in peer relations) in terms of independent resource acquisition because insecure girls cannot rely on their parents under extreme high-risk environmental conditions.

Guttmann-Steinmetz and Crowell (Reference Guttmann-Steinmetz and Crowell2006) provide a conceptual model demonstrating that externalizing behavior by children develops from parental failure to provide a secure base to protect children from environmental risks. With the recent development of measures of attachment quality during middle childhood (Finnegan et al. Reference Finnegan, Hodges and Perry1996; Kerns et al. Reference Kerns, Tomich, Aspelmeier and Contreras2000), a line of research has emerged suggesting that girls' aggression is associated with avoidant rather than ambivalent attachment style. No gender differences were found in the association between avoidant attachment and aggression (Davies & Forman Reference Davies and Forman2002; Granot & Mayseless Reference Granot and Mayseless2001). Finnegan et al.'s (Reference Finnegan, Hodges and Perry1996) research showed that for both sexes, aggression was predicted by an avoidant strategy but not by a preoccupied strategy, according to their specific linkage hypothesis. More recent research (Booth-LaForce et al. Reference Booth-Laforce, Oh, Hayoung Kim, Rubin, Rose-Krasnor and Burgess2006) showed that avoidant coping in relation to the mother, and lower security with the father, was related to aggression. These associations did not vary by sex of child. In addition, in order to reduce the risk of retaliation, girls are more likely to use subtle forms of aggression such as relational aggression or coercive and prosocial strategies of resource control (i.e., bi-strategy; Hawley Reference Hawley, Hawley, Little and Rodkin2007) to compete for resources, such as better-resourced men (Campbell Reference Campbell1999). Active reaction (the correlates of avoidant attachment) to secure a scarce resource is likely to be more effective than a passive one (the correlates of ambivalent attachment).

We would expect insecure females to be more likely to adopt avoidant rather than anxious strategies to maximize current reproductive success, no matter how challenging the environment is,Footnote ² because there is very limited support for the proposal that an anxious strategy enhances partner investment or reproductive success. However, “avoidant” women who show little desire for commitment and adopt a short-term mating strategy (Feeney Reference Feeney, Cassidy and Shaver1999; Gentzler & Kerns Reference Gentzler and Kerns2004) by mating with multiple males could acquire considerable resources and simultaneously reduce the possibility of future male attacks against her and her offspring (Hrdy Reference Hrdy1981).

In accordance with Del Giudice's hormonal basis of the middle childhood transition, we now consider the evidence for the role of oxytocin (OT) in females' avoidant attachment. OT is closely implicated in female behavior because its effects are strongly modulated by estrogen. Early social experience can alter social behavior by affecting the development of neuroendocrine systems including OT (see Cushing & Kramer Reference Cushing and Kramer2005, for a review). In rats, female offspring raised by high-licking and high-grooming mothers show a significant increase in oxytocin receptors, OTRs (Francis Young et al. Reference Francis, Young, Meaney and Insel2002). Furthermore, changes in the oxytocinergic system in response to social interaction could alter brain development and, thereby, the subsequent expression of social behavior. However, OT has little or no effect on regions of the brain in adults due to a lack of receptors, compared with before adolescence (Cushing & Kramer Reference Cushing and Kramer2005). Thus, middle childhood appears to be the “last chance” for OT to exert long-lasting effects on behavior. In a high-risk environment lacking sufficient parental investment, we would expect to see a decrease in oxytocin affecting the childhood organization and development of the brain and resulting in an increase in aggression among girls with insecure attachments. In an environment in which well-resourced males are in short supply, it would seem adaptive that female competition and female assault (see Campbell Reference Campbell1999) would be primed by epigenetic mechanisms of early social experience (Cushing & Kramer Reference Cushing and Kramer2005).

Overall, we welcome and accept most of Del Giudice's arguments as a significant contribution to our understanding of the development of attachment from an evolutionary perspective. However, Del Giudice's analysis of insecure attachment in females should include avoidant pattern, which should be further examined empirically.