Lee et al. only men with good innate immune functioning can changes the ass ound. n th tephen,Clark.Penton 1975)Supporting this im handicap hypothesis.research shows that facial mascu- quantify the masculinity of facial shape in photographs linity is positively associated with circulating testosterone of a large sample of identical and nonidentical (same-sey nton-Voak Chen,2004),and ma and opposit metric. Chan.Simmons,2003 Thorhl remale facial mas Fin sexual conflict by assessing the correlation in facial mas. Gangestad,2006).An alternative (or additional)explana culinity betw in the for greater attractiveness of male offspring.This situation can create a self-reinforcing runaway effect that exaggerates ce and the preferred trait (Fisher,1915; Method 20 The iden that ulinity signals heritabl Participants genetic quality,manifested as immunoco petence.sexv Participants were 1.193 individual twins and 106 of their sons,or both,has gained broad acceptance(Ga gestad Scheyd,2005;Gangest 2010 1 Clark.Boothrovd.Penton-voak 2012)However.this day (mean age =16.03 years,SD=0.47 years),and their idea depends on two key assumptions that have not been siblings were tested and photographed as close as pos adequately tested.First, is assume that male facia of thu participant tion):otherwise it could not be inherited by offs rom the Human Research Ethics Committee at OIMR Berghofer. genes that increase male facia mascu lnity are by any genetic benefits to male offspring would be counter acted by the detriment to female offspring(this is termed n2011 ak digi waves wer Comwell and 2008)em pirically addr under standard indoor lighting these assumptions by analyzing ratings of masculinity measures of masculinity and subjective ratings of mascu- sof the faces linity and attractiveness were obtained from these wer ndent raters identified a total of 18 land members of a standard nuclear family qually share both marks on each face.Raters we ined fo eral week genes and family environment,which are therefore com in hour-long sessions in which landmarks were defined pletely confounded In another study,Mitchem et a anatomically.Figure I shows the location of each land al ph or mon and mark.I were randoml n Ior eac of and family s to dis as them pixel location chosen by these and attractiveness again,however,no objective mea Photographs of participants were not originally taken sures were used.It has been show previously that sub for shape analysis. re,the photographs varie on addit ways tha than morphologica masculinity, icipant's capt 2 Lee et al. only men with good innate immune functioning can afford to support the levels of testosterone required to develop masculine facial features (Folstad & Karter, 1992; Zahavi, 1975). Supporting this immunocompetence￾handicap hypothesis, research shows that facial mascu￾linity is positively associated with circulating testosterone levels (Penton-Voak & Chen, 2004), and male facial mas￾culinity has been found to correlate positively with both perceived and actual health (Rantala et al., 2012; Rhodes, Chan, Zebrowitz, & Simmons, 2003; Thornhill & Gangestad, 2006). An alternative (or additional) explana￾tion of the relevance of male facial masculinity to genetic quality is the sexy-son hypothesis, according to which the genetic benefits to offspring come in the form of greater attractiveness of male offspring. This situation can create a self-reinforcing runaway effect that exaggerates both the preference and the preferred trait (Fisher, 1915; Huk & Winkel, 2008). The idea that male facial masculinity signals heritable genetic quality, manifested as immunocompetence, sexy sons, or both, has gained broad acceptance (Gangestad & Scheyd, 2005; Gangestad & Simpson, 2000; Little, Jones, et al., 2011; Perrett et al., 1998; Rantala et al., 2012; Roberts & Little, 2008; although see Puts, 2010; Scott, Clark, Boothroyd, & Penton-Voak, 2012). However, this idea depends on two key assumptions that have not been adequately tested. First, it is assumed that male facial masculinity is substantially heritable (i.e., a substantial proportion of the variation is due to additive genetic vari￾ation); otherwise, it could not be inherited by offspring and could not signal good genes. Second, it has been assumed that the genes that increase male facial mascu￾linity are not detrimental to female offspring (e.g., by increasing their facial masculinity, which has been shown previously to decrease female attractiveness); otherwise, any genetic benefits to male offspring would be counter￾acted by the detriment to female offspring (this is termed intralocus sexual conflict; see Bonduriansky & Chenoweth, 2009; Garver-Apgar, Eaton, Tybur, & Thompson, 2011). Cornwell and Perrett (2008) empirically addressed these assumptions by analyzing ratings of masculinity and attractiveness of the faces in family photographs. However, no objective measures of masculinity were used, and heritability could not be estimated because members of a standard nuclear family equally share both genes and family environment, which are therefore com￾pletely confounded. In another study, Mitchem et al. (2013) used facial photos of monozygotic (identical) and dizygotic (nonidentical) twins to distinguish the influence of genes and family environment on facial masculinity and attractiveness; again, however, no objective mea￾sures were used. It has been shown previously that sub￾jective ratings of masculinity are based on additional factors other than morphological masculinity, which changes the association with traits such as attractiveness (Scott, Pound, Stephen, Clark, & Penton-Voak, 2010). In the research reported here, we used geometric mor￾phometrics, the statistical analysis of shape, to objectively quantify the masculinity of facial shape in photographs of a large sample of identical and nonidentical (same-sex and opposite-sex) twins and siblings. Using biometrical modeling, we estimated the heritability of male and female facial masculinity. Finally, we tested for intralocus sexual conflict by assessing the correlation in facial mas￾culinity between opposite-sex twins and siblings, and we investigated the relationship, for each sex, between the objective masculinity and rated attractiveness of the photographs. Method Participants Participants were 1,193 individual twins and 106 of their siblings from 575 families who took part in the Genes for Cognition study and were part of the Brisbane Adolescent Twin Studies (Wright & Martin, 2004). Twins were tested and photographed as close as possible to their 16th birth￾day (mean age = 16.03 years, SD = 0.47 years), and their siblings were tested and photographed as close as pos￾sible to their 18th birthday (mean age = 17.80, SD = 0.46). All participants gave informed written consent, and approval to code and analyze these data was obtained from the Human Research Ethics Committee at QIMR Berghofer. Photographs Photographs of participants were taken between 1996 and 2010. In the earliest waves of data collection, photo￾graphs were taken using film cameras and later scanned to digital format. Photographs from later waves were taken with digital cameras. Each photograph was taken under standard indoor lighting conditions. Objective measures of masculinity and subjective ratings of mascu￾linity and attractiveness were obtained from these photographs. Ten independent raters identified a total of 18 land￾marks on each face. Raters were trained for several weeks in hour-long sessions in which landmarks were defined anatomically. Figure 1 shows the location of each land￾mark. Two raters were randomly chosen for each land￾mark, and the coordinate for that landmark was calculated as the mean pixel location chosen by these two raters. Photographs of participants were not originally taken for shape analysis. Therefore, the photographs varied in ways that could alter the shape information captured by the landmarks (e.g., the participant’s head angle facing Downloaded from pss.sagepub.com by Cai Xing on January 7, 2014