Human physique and sexual attractiveness

Masculine Somatotype

A number of studies have produced evidence that women find certain types of masculine physique more attractive sexually. A broad chest and shoulders, narrow hips, and a muscular torso are important traits which influence female assessments of masculine physical attractiveness (Lynch and Zellner 1999; Dixson et al. 2003). In order to quantify these preferences, some studies have made use of Sheldon's (1940) system of somatotyp-ing. This classifies human physique according its degree of mesomorphy (muscular and powerful build), ectomorphy (slim and lean build), and endo-morphy (heavy-set and fatter build). Examples of pronounced mesomorphic, ectomorphic, and endo-morphic somatotypes are shown in Figure 7.6, along with an intermediate, or average, type of physique. Images of this kind, back-posed to avoid the distraction of facial cues and standardized for height and posture, have been used in cross-cultural studies to measure female preferences for masculine physique (Dixson et al. 2003; Dixson et al. 2007a; 2007b; in press). Results of studies conducted in China, New Zealand, USA, and Cameroon are summarized in Figure 7.7. In each case the images were modelled to include skin colour and hair appropriate for the population considered. In all these countries

Somatotypes Figures
Figure 7.6 Back-posed images of male somatotypes ( (A) ectomorphic; (B) mesomorphic; (C) average; (D) endomorphic) used in cross-cultural studies of masculine physique and sexual attractiveness. Results of some of these studies are shown in Figure 7.7.

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Figure 7.7 Women's ratings of the attractiveness of the four masculine somatotypes depicted in Figure 7.6. In China, New Zealand, USA, and Cameroon, women gave the highest ratings to mesomorphic and average somatotypes. *P < .05; ***P < .001. Source: Data (means ± SEM) are from Dixson et al. (2007a; 2007b; and in press).

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Figure 7.7 Women's ratings of the attractiveness of the four masculine somatotypes depicted in Figure 7.6. In China, New Zealand, USA, and Cameroon, women gave the highest ratings to mesomorphic and average somatotypes. *P < .05; ***P < .001. Source: Data (means ± SEM) are from Dixson et al. (2007a; 2007b; and in press).

mesomorphic and average somatotypes received the highest ratings for sexual attractiveness, whilst the endomorphic physique was least preferred. The ectomorph did not receive the highest ratings in any of the populations studied, but this image did receive proportionately higher scores in China (Figure 7.7) and in Sri Lanka than in some other countries. Thus, some cultural variations probably exist in female preferences. As a second example of such differences, a mesomorphic somatotype was rated as significantly more attractive than an average male physique in UK, whereas the reverse was true in China.

Sheldon's original ideas concerning somatotyp-ing, published in his Varieties of Human Physique (Sheldon, Dupertuis, and McDermott 1940) and the Atlas of Men (Sheldon, Dupertuis, and McDermott 1954), have been much criticized and refined over the years (Carter and Heath 1990). While measures of somatotype and body composition are not synonymous, it is fair to say that pronounced endo-morphy equates to a significantly fatter body build, whilst mesomorphy, such as is represented in Figure 7.6, is indicative of a higher overall muscle mass. Mesomorphy is associated with greater physical strength and aptitude for pursuits requiring speed, strength, and stamina (Carter and Heath 1990). Ectomorphy, by contrast, is consistent with a less powerful physique, and endomorphy may be associated with greater risk of cardiovascular disease and diabetes (Katzmarzyk et al. 1998; Bolunchuk et al. 2000). Thus, female preferences for average or mesomorphic physiques may be related to the fact that such traits provide reliable signals of masculine health, strength, and fitness. These traits may have been of considerable importance in human evolution, given selective pressures upon males to compete with each other, protect their families and to display competence in hunting, scavenging, and other skills required for survival and successful reproduction (Ellis 1992; Buss and Schmidt 1993; Bramble and Lieberman 2004).

Bramble and Lieberman stress the likely importance of endurance running during evolution of the genus Homo. This might have been especially relevant to the success of hunting large game in open African savannah environments prior to the development of sophisticated weaponry. Persistence hunting survived until very recently among the !Xo and /Gwi bushmen of the central Kalahari in Botswana. Liebenberg (2006) has provided valuable information on the tracking and survival skills used by small groups of these hunters in pursuit of prey such as kudu, hartebeest, and gemsbok. The persistence method of hunting provided these bushmen with significant amounts of meat, although not as much as could be secured by hunting with dogs (Table 7.3). For the earliest precursors of human beings in Africa, such as H. ergaster,

Table 7.3 Persistence hunting: success rates as compared to other hunting methods used by the !Xo and /Gwi hunter-gatherers of the Kalahari

Hunting method Days tried Attempts Successes (%) Kills (per day) Yield (kg/day)

Persistence 46 2

Dogs 5 5

Bow and arrow 46 41

Club and spear 46 11

Spring-hare probe 46 29

Source: After Liebenberg (2006).

equipped with only the most primitive technology, it is possible that endurance running and persistence hunting were crucial elements in the evolution of their hunter-gatherer cultures. Leibenberg concludes that 'before the domestication of dogs, persistence hunting may have been one of the most efficient forms of hunting. Endurance running and persistence hunting may therefore have been crucial factors in the evolution of humans.'

Human mate choice is an exceedingly complex subject, and cross-culturally the sexes exhibit an array of preferences for particular traits in long term partners, including aspects of personality, such as kindness and a good sense of humour (Buss 1989). However, in response to images offering a choice of masculine somatotypes, women consistently choose either men of average or muscular physique. Probably, the ideal lies somewhere between these two somatotypes. Honed by natural selection during human evolution, the more muscular physique of men conveyed advantages in hunting and survival. Inter-male competition for access to mating partners was probably also instrumental in moulding the evolution of masculine physique, as was female mate choice for the physically most healthy and able males. The preferences expressed by women in modern day human cultures (Figure 7.7) may thus reflect the results of natural and sexual selection acting upon our African ancestors.

Masculine stature

Like sexual dimorphism in body weight, sex differences in height are characteristic of human populations worldwide (Figure 7.2). Although stature varies considerably between human populations, men within each population tend on

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average to be taller than women. It is also the case, cross-culturally, that women express a preference for marriage partners who are slightly taller than themselves (Pawlowski 2003). Taller men have greater reproductive success (Pawlowski, Dunbar, and Lipowicz 2000; Nettle 2002). Leg length contributes to overall assessments of human stature and may thus affect judgements of attractiveness. Sorokowski and Pawlowski (2008) report that this is the case but increasing the leg lengths of images only enhances their attractiveness if the changes are small (5 per cent) and in true proportion to the overall height of the figures. As with masculine body weight and composition, it is likely that sexual selection as well as natural selection has played a significant role in the evolution of sex differences in human stature.

Among the extant apes, the hind limbs are relatively short. Although the australopithecines were capable of bipedal locomotion, their legs were of intermediate length, and it is with the advent of the genus Homo that stature increases markedly, perhaps in association with transitions to a hunter-gatherer mode of life. Thus, estimates of average stature in australopithecines such as A. afarensis (128 cm) and A. africanus (124.4 cm) are much less than for H. ergaster (185 cm), H. erectus (166.5 cm), H. neanderthalensis (165 cm), or for modern H. sapiens (Collard 2002). Carrier (2007) has advanced the interesting hypothesis that the short legs of great apes may be adaptive not only during climbing, but also during inter-male aggression. Carrier argues that males benefit from having a lower centre of gravity when they stand erect (as during the charging displays of male chimpanzees, or the chest-beating displays of silverback gorillas) or when they fight, by increasing the leverage exerted through the upper body and arms. Fights between males can be severe in chimpanzees (Goodall 1986), and although fights are infrequent between silver-backs, they can be intense (Harcourt 1978). The same is the case for aggression between mature male orangutans (Galdikas 1985b). Injuries due to fighting have been documented in skeletal studies of all these species and more so among males than females (Lovell 1990; Jurmain 1997). The australopithecines had relatively short legs, intermediate in length between those of the great apes and Homo, and Carrier points out that this feature persisted 'for over two million years, or approximately 100,000 generations'. This may have been connected to patterns of inter-male aggression which benefited from having shorter legs and a lower centre of gravity, as among the extant apes. We should keep in mind, however, that retention of somewhat shorter legs in the australopithecines may have been associated primarily with their locomotor specializations, which included climbing in arboreal environments, as well as terrestrial, bipedal locomotion. Lengthening of the legs in the genus Homo, may equally reflect shifts in ecological specialization towards an exclusively terrestrial existence and an increased ability to walk and run for long distances.

Current interpretations of the fossil evidence encourage the view that male australopithecines were larger than females; this is consistent with significant levels of inter-male competition such as may occur in polygynous or multi-male/multi-female mating systems (however, see Chapter 1, for a critique of evidence on sexual dimorphism in australopithecines). With the emergence of the genus Homo and the growth of inter-male competition involving tool use, the ability to run for long distances, and to combine physical strength with enhanced intellectual abilities, the advantages of short stature would have decreased. Indeed, sexual selection is likely to have favoured female preferences for taller partners who were more successful in these new kinds of inter-male competition, hunting, and survival skills. The preference which many women currently express for a taller long-term partner may thus also reflect ancient traits, developed in forms such as H. ergaster and incorporated into the mate-choice systems of H. sapiens.

The female hourglass figure: Singh's hypothesis

As well as significant sexual dimorphism in stature, body weight and body composition in human beings, there are marked sex differences in body shape between men and women. These differences emerge during puberty and adolescence. In women, oestrogenic stimulation results in greater deposition of fat in the buttocks, thighs, and breasts. In men, by contrast, testosterone promotes greater muscular development, and fat is laid down in the abdominal region, rather than in the buttocks, thighs, or breast area (Harrison et al. 1988; Rebuffe-Scrive 1991). Women therefore accumulate more fat than men in the lower part of their bodies (a gynoid body shape), with slimmer waists and broader hips, accentuating the skeletal sex difference in the pelvis. The waist-to-hip ratio (WHR) is a simple measure of this sexual dimorphism in adult body shape. The circumference of the waist, at its narrowest point, is divided by the circumference of the hips; in women the resulting WHR ranges from 0.67-0.80 (in healthy pre-menopausal subjects) whereas in men higher values (0.85-0.95) are the norm (data collected in Finland: Marti et al. 1991). Singh has conducted a series of studies in order to examine the role of female WHR in male mate choice. He proposes that a low WHR, such as occurs in young, non-pregnant women, is indicative of a healthy distribution of body fat and consistent with a fertile and reproductively advantageous physiology. Masculine preferences for women possessing a narrow waist and an hourglass figure may thus have been favoured by sexual selection during human evolution (Singh 2002, 2006).

There is evidence that the female WHR might provide an honest signal of health and reproductive potential. Possession of a narrow waist and large breasts correlates with the production of higher levels of oestrogen during the follicular phase of the menstrual cycle (Jasieriska et al. 2004), whereas women with high WHRs tend to have more irregular cycles or to fail to ovulate (Moran et al. 1999; Van Hooff et al. 2000). Women who suffer from poly-cystic ovarian syndrome, which is characterized by increased secretion of testosterone, reductions in oestrogen secretion and infertility problems, have higher WHRs than healthy women in the same age range (Pasquali et al. 1999; Velasquez et al. 2000). The hormonal changes and loss of fertility which occur at the menopause in women are also associated with shifts to higher WHRs (Arechiga et al. 2001).

Singh (2002) stresses that it is the 'interaction between WHR and body mass index (BMI) that affects health status and healthiness'. The body mass index (BMI) is a measure of weight, scaled for height (body weight in kilograms is divided by height in metres squared, to yield the BMI). However, measurements of the BMI alone do not capture the important sex differences in body shape and fat distribution which Singh implicates in men's ratings of female sexual attractiveness and health. Singh (1994) asked physicians of both sexes to rate the health and attractiveness of line drawings of female body shapes which varied in BMI (underweight, average, and overweight) and in four levels of WHR; examples of the drawings he used are shown in Figure 7.8. The results closely paralleled those obtained in an earlier study involving subjects who were not health professionals. Figures with a lower WHR (especially the 0.7 WHR images) were rated as more healthy, youthful, and attractive in both studies. The highest ratings were given to the average-weight female figure having a 0.7 WHR; underweight and overweight figures were not rated as highly for health or attractiveness, even when manipulated to have low WHRs.

A challenge for studies of the evolution of human morphology is the requirement to obtain data from a sufficiently wide range of cultures, given the variations in physique and sexual preferences which occur in different parts of the world. Some cross-cultural studies indicate that men might prefer a higher female WHR (Yu and Shepard 1998; Wets-man and Marlowe 1998) but I do not consider that these findings invalidate Singh's hypothesis. Yu and Shepard collected data in Peru from an indigenous population (the Matsigenka) living in a remote, protected area of the Manu National Park. Interestingly, men rated images of women with a 0.9 WHR as most attractive and healthy. However, it is important to note that Yu and Shepard used only images of women with either a 0.7 or a 0.9 WHR, rather than providing a range of images (e.g. no 0.8 WHR was available). The Matsigenka, like some other South American indigenous Indian cultures, tend to be quite thick-set in physique. The 0.7 WHR image may have appeared unusual, and less healthy for this reason; the only alternative choice being a 0.9 WHR female image. The line drawings used were the same as those in Singh's studies; front-posed, clothed in western-style bathing costumes and of Caucasian appearance (skin colour and hair style). This was also inappropriate, as it is important to use images which are relevant to the culture that is being sampled. Frank Marlowe's studies of the Hadza hunter-gatherers in Tanzania provide an

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Figure 7.8 Examples of the line drawings of women, varying in waist-to-hip ratio (WHR) and body weight, used by Singh in studies of female WHR and attractiveness.

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Figure 7.8 Examples of the line drawings of women, varying in waist-to-hip ratio (WHR) and body weight, used by Singh in studies of female WHR and attractiveness.

Source: From Dixson (1998a) and by courtesy of Professor D. Singh.

excellent example of this principle. Initially, Wets-man and Marlowe (1998) reported that Hadza men prefer images of women with higher WHRs. These investigators also used Singh's front-posed, line drawings of Caucasian women. However, Hadza men expressed their interest in viewing images of women which include the buttocks, as these are important in their judgements of attractiveness. Accordingly, a subsequent study (Marlowe, Api-cella, and Reed 2005) used side-posed images of women; men's preferences for a 0.6 WHR emerged once they could assess images which included the buttocks (Figure 7.9A).

In our cross-cultural studies we have used back-posed images of women (Figure 7.9B). The results of this work confirm that men rate images of women having a slim waistline and a low WHR as most attractive sexually and as most desirable partners for a long term relationship. As examples,

Figure 7.10 shows data on men's preferences collected in China, New Zealand, USA (California) and Cameroon. In each case, the same set of six back-posed female images was used, ranging in WHR from 0.5 to 1.0, but adapted to have skin and hair colours appropriate for each culture. It is clear from these studies, as well as others using different images, that men prefer female WHRs ranging from 0.6 to 0.8. Values within in this range are rated as more attractive and marriageable than are high WHRs (0.9-1.0). A WHR of 0.7 is not a universal preference, therefore, and we should not expect it to be so. Recall that, in Finland, healthy women of reproductive age have WHRs ranging from 0.67 to 0.8. It is reasonable to expect that sexual selection might have favoured male preferences within this range, and that the same might apply in different populations worldwide.

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