The target article provided an evolutionary account for the financial and prosocial biases in favor of attractive people. Within the framework of a mating-related evolutionary model, Maestripieri et al. argued that the mating motivations lead to a strong bias in favor of attractive individuals in adults. However, this evolutionary model did not explain the development of attractiveness-related biases in section 6 in the target article – that is, (1) children's positive biases toward attractive individuals (including same-age peers and adults) and (2) adults' positive biases toward attractive children. In this commentary, I integrate the ideas about the mating-related evolutionary model with another evolutionary theoretical model (i.e., life history theory), which may provide different functional explanations for the positive biases in favor of attractive people.

Life history theory examines how evolved mechanisms affect development throughout the life span (Del Giudice et al. Reference Del Giudice, Gangestad, Kaplan and Buss2015; Griskevicius et al. Reference Griskevicius, Delton, Robertson and Tybur2011; Hill & Kaplan Reference Hill and Kaplan1999). Natural selection produces development-related energetic and resource allocations between somatic effort (i.e., the growth and maintenance of one's body) and reproductive effort (i.e., mating and caregiving). An optimal life history trade-off is resolved by the coordinated tuning of multiple physiological (e.g., endocrine, hemostasis, and immunity) and psychological (e.g., behavior, cognition, and attitude) systems, which constantly assess environmental constraints and accordingly calculate the energetic allocations (Del Giudice et al. Reference Del Giudice, Gangestad, Kaplan and Buss2015). As an example, physical attractiveness can be seen as adaptive strategies in response to different environmental challenges inherent in the life history traits (Sugiyama Reference Sugiyama and Buss2015). Attractiveness-related social judgment biases may reflect different fitness-promoting aspects of social motives over the life span (Kenrick et al. Reference Kenrick, Griskevicius, Neuberg and Schaller2010).

First, given that individuals before puberty have no mating motivation, the mating-related evolutionary model by Maestripieri et al. did not explain why they still have positive biases toward attractive people. According to the life history theory, in infancy and childhood, survival is the main task and challenge (Bogin Reference Bogin1997; Bowlby Reference Bowlby1969; Chen & Chang Reference Chen and Chang2012). So immature individuals' preferences for attractive faces represent a self-protection strategy to increase their opportunity for survival, because attractive faces commonly indicate less danger (Rhodes Reference Rhodes2006). For example, adults with attractive faces are perceived to afford more warmth, honesty, and naïveté and less danger than those with less attractive faces (Berry & McArthur Reference Berry and McArthur1986; Berscheid & Walster Reference Berscheid, Walster and Berkowilz1974). Because of the importance of the fitness-relevant information conveyed by attractive faces, the positive biases in favor of attractive people may have been selected in young infants.

Second, I question the prediction by Maestripieri et al. that greater attractiveness-related positive biases in infancy might be linked to greater positive biases toward attractive opposite-sex individuals starting from adolescence. The latter may reflect underlying motives associated with mating. It seems to suggest that infants' preference for attractive faces may be functionally prepared for the expression of biases to fulfill mating-relevant goals later. However, the existing evidence suggests that their hypothesized effects are rather weak. I argue that the attractiveness-related biases in infancy may reflect underlying motives associated with survival/self-protection rather than mating. To give an example, infant preferences for attractive faces are apparent for strangers' faces (Langlois et al. Reference Langlois, Roggman and Rieser-Danner1990). Specifically, infants show higher levels of withdrawal and distress toward an unattractive stranger, whereas they show higher levels of positive affection and interactions with an attractive stranger. This means that selective preferences for attractive faces when infants interact with a stranger can represent one of the behavioral strategies activated by the attachment behavioral system to promote safety and survival. However, it should be noted that such selective preferences are not likely to affect infant behavior toward familiar caregivers because of the importance of the attachment relationships between infants and familiar caregivers (Langlois et al. Reference Langlois, Roggman and Rieser-Danner1990).

Given the different evolutionary functions underlying the biasing effects of attractiveness, the life history model also explains age differences in attractiveness biases toward opposite-sex and same-sex individuals over the life span. For example, there is no clear evidence for positive attractiveness biases toward opposite-sex people in infant and childhood (Dion Reference Dion1973; Langlois et al. Reference Langlois, Ritter, Roggman and Vaughn1991; Saxton et al. Reference Saxton, Caryl and Roberts2006). However, starting from adolescence, mating is the main goal. Therefore, there is a rapid increase in positive biases toward attractive opposite-sex people in adolescence (Agthe et al. Reference Agthe, Spörrle, Frey, Walper and Maner2013). These sexually mature individuals' preferences for the attractive opposite-sex face represent a strategy to increase their opportunity for reproduction (Kościński Reference Kościński2011), because physical attractiveness is an indicator of overall quality, including greater genetic quality, as discussed in the target article. The age changes in attractiveness-related biases further reflect the fundamental life history trade-offs between somatic and reproductive effort.

Last, given that adults have positive biases toward attractive children not because of their mating motivation, the mating-related evolutionary explanation by Maestripieri et al. is obviously inappropriate. However, according to the life history model, adults (especially parents) may invest more in attractive than in unattractive infants because infant attractiveness may signal health and competence (Rhodes et al. Reference Rhodes, Zebrowitz, Clark, Kalick, Hightower and McKay2001b; Ritter et al. Reference Ritter, Casey and Langlois1991), which may consequently enhance adults' reproductive fitness (Beaulieu & Bugental Reference Beaulieu and Bugental2008). A large and convergent body of literature (e.g., Allen et al. Reference Allen, Wasserman and Seidman1990; Barden et al. Reference Barden, Ford, Jensen, Rogers-Salyer and Salyer1989; Field & Vega-Lahr Reference Field and Vega-Lahr1984) indicates generally that compared with parents of normal children, parents of children with various types of congenital anomalies (mainly craniofacial anomalies) showed more negative parental behaviors (e.g., controlling) and fewer positive parental behaviors (e.g., responsiveness and warmth). Even in the normal sample, mothers showed higher levels of positive interactions with more attractive infants compared with less attractive infants (Langlois et al. Reference Langlois, Ritter, Casey and Sawin1995). Therefore, these studies all suggest that parental differential preference and investment in their children as a function of cues to the child's reproductive value may reflect their life history trade-off.