the integration of LH theory into models of human development has helped to revolutionize the field, we should not think of LH strategies as becoming immutable due to early infant attachment experiences. Some evolutionary theorists believe that LH strategies are not prescribed at an early stage in development but rather show a degree of flexibility, based around a series of developmental switch point transitions. This notion of transitions in development is particularly associated with Marco Del Giudice. According to Del Giudice, during development there are a series of points when the LH strategy might be attenuated leading to changes in social behavior during childhood.
It is worth noting that the concept of switch points grew out of the work of classical ethologists who introduced the earlier notion of critical or sensitive periods where an organism is particularly likely to learn specific information (West‐Eberhard, 2003). An example of this is that young animals of many species, such as domestic chicks and greylag geese, become imprinted on their mother during the first few days or weeks of life (Lorenz, 1935; Workman et al., 2000). Each switch point is related to adaptive challenges that appear at stages in development. While there may be a switch point even prior to birth (where a fetus might, for example, respond to maternal stress hormones), the most important one for our purpose is the juvenile transition. This switch from early to middle childhood occurs between 6–8 years of age in industrialized societies and is a period of rapidly increasing social activities with peers (Del Giudice 2009a, 2009b; Del Giudice & Belsky, 2011). According to Del Giudice this 2‐year switch point can be likened to the critical/sensitive periods that ethologists earlier outlined for various species. During and after this switch point in development, children begin to strive for social dominance and acceptance among peers. They also increase their level of competitive and social play as they compete to be considered socially attractive individuals (Smith, 2005). During the juvenile transition there is a peak in sexually differentiated behavior and the beginnings of romantic attractions (Del Giudice & Belsky, 2011).
According to Del Giudice this juvenile transition serves three adaptive roles:
Coordinating the expression of a suite of LH related traits such as attachment, cooperation, and stress regulation.
Organizing sexually differentiated behavior such as dominance, mating‐oriented strategy, and levels of potential physical aggression.
Providing a period of assessment prior to the onset of reproductive‐related behaviors.
According to Del Giudice this adaptive conception of the juvenile transition is supported by studies that show how agonistic stress experienced at this age and over the early years of adolescence affects the type of mating strategy later adopted (Davis & Were, 2007). Moreover, this juvenile transition is mediated by a boost in the secretion of androgens at this point in development (6–8 years), known as “adrenarche” due to hormones being secreted by the adrenal glands a few years prior to puberty (Auchus & Rainey, 2004). This is suggestive that changes in both prosocial and antisocial behavior during the juvenile transition are related to later reproductive strategies. Due to feedback from his peers, for example, a physically robust boy is more likely to develop a dominant role in peer relationships and this may have‐knock‐on effects later in life with regard to his mating strategy.
Del Giudice also considers how reproductive strategies related to the juvenile transition are attenuated by social feedback around the age of six to eight. Consistent with Belsky’s model, he suggests that adrenarche is brought forward by earlier family stress. This means that Del Giudice’s LH model, while incorporating elements of Belsky’s psychosocial acceleration theory, also considers social feedback from peers during the period 6–8 years of age.
Do Parents Matter? Judith Rich Harris and the Nurture Assumption
While Del Giudice builds in the importance of peers to his model of children’s social developmental pathway, another developmentalist, also influenced by evolutionary theory, took this one step further. In 1995 Judith Rich Harris proposed that the main socializing agents during a child’s development are the genes the child inherits and the child’s peer group. This left little or no room for parental influence. This astonishing proposal was based, in part, on reports by behavioral geneticists that around 50% of the variability between children can be accounted for by genetic differences between them and between 0 to 10% by differences due to the shared parental environment (Plomin & Daniels, 1987, see also Plomin, 2018). Such findings are based on studies of individuals who vary in genetic relatedness such as twins (identical and fraternal), siblings, and step‐siblings who are either raised in the same household or in a different one. By studying various correlational scores on a range of tests between such groupings of children, behavioral geneticists found that, in terms of personality, siblings reared apart are no more different to each other than siblings reared together. In contrast, adopted siblings are no more similar to each other than to anybody chosen at random from the general populace. If 50% of the variance is accounted for by shared genes and 0–10% by shared parental environment then, Harris asked, where was the missing 40–50% variance?
In her 1995 article she suggested that the missing variance can be traced back to peer‐group relationships. Drawing on a knowledge of human evolution and the behavior of current forager societies, Harris suggested it made sense to gravitate towards the norms and social mores of a child’s peer group rather than those of the parents because children have different (and often competing) interests to parents. It is not always in the child’s best interest to learn what parents want them to learn. Rather, it pays them to adopt the social norms of their peer group as these are the individuals that will become their allies, competitors, and eventually mating partners.
Because she considers children of school age are socialized largely by their peer group, Harris called this the group socialization (GS) theory. She later brought this theory to wider public attention via her books, The Nurture Assumption (1998, 2009) and No Two Alike (2006). From the outset, Harris’s GS theory split the field. While most evolutionary psychologists were positive about her theory, including the prominent Harvard psycholinguist Steven Pinker (who incorporated her ideas into his book the Blank Slate, 2002), many developmentalists were unconvinced. Deborah Vandell (2000), for one, has suggested that, in focusing on peer groups, Harris ignores sibling and teacher influences on a child’s social development. She also queries the fact that Harris appears to assume all relations between a child and its parents’ behavior can be considered the result of either direct genetic factors or of gene–environment correlations (meaning that this variance can all be traced back to shared genes). Vandell suggests instead that Harris should have considered the possibility of a parent’s behavior influencing the child’s development independently of the genes they share. Another developmentalist who has reservations about Harris’s GS theory is Craig Hart. Alongside other criticisms, Hart (2007) suggests that parents influence what children do outside the home, which might thereby diminish Harris’s argument for peer group socialization. He is also critical of Harris’s claim that many parent‐to‐child influences on social development might, in reality, be child‐to‐parent influences, citing research that suggests bidirectional parent–child interactions. We might also ask, does her GS theory contradict Bowlby and Ainsworth’s view that early mother–infant attachment strongly influences later social behavior?
Today, Harris’s GS theory continues to divide developmentalists (Harris & Workman, 2016; Pinker 2020). Despite the apparent hardline stance of protagonists on either side of the debate, Belsky has suggested a possible synthesis between the two camps. In 2005, he argued that children vary in their susceptibility to parental influence and this, in itself, might be considered an adaptation. He suggested that, under some environmental conditions, being more susceptible to parental influence might be adaptive whereas under other conditions being influenced by peers might also be adaptive. Parental influence may work well when the environment is stable because their ways of doing things will continue to lead to success. When, however, the environment is changeable, then it
