Susan F. Lipson

Large breasts and narrow waists indicate high reproductive potential in women

Physical characteristics, such as breast size and waist–to–hip ratio (WHR), function as important features used by human males to assess female attractiveness. Males supposedly pay attention to these features because they serve as cues to fecundity and health. Here, we document that women with higher breast–to–underbreast ratio (large breasts) and women with relatively low WHR (narrow waists) have higher fecundity as assessed by precise measurements of daily levels of 17–β–oestradiol (E2) and progesterone. Furthermore, women who are characterized by both narrow waists and large breasts have 26% higher mean E2 and 37% higher mean mid–cycle E2 levels than women from three groups with other combinations of body–shape variables, i.e. low WHR with small breasts and high WHR with either large or small breasts. Such gains in hormone levels among the preferred mates may lead to a substantial rise in the probability of conception, thus providing a significant fitness benefit.

Men in committed, romantic relationships have lower testosterone.

Variation in human male testosterone levels may reflect, and effect, differential behavioral allocation to mating and parenting effort. This proposition leads to the hypothesis that, among North American men, those involved in committed, romantic relationships will have lower testosterone levels than men not involved in such relationships. Our study is the first to examine whether being in such a relationship (rather than being married) is the meaningful predictor of male testosterone levels. To test this hypothesis, 122 male Harvard Business School students filled out a questionnaire and collected one saliva sample (from which testosterone level was measured). Results revealed that men in committed, romantic relationships had 21% lower testosterone levels than men not involved in such relationships. Furthermore, the testosterone levels of married men and unmarried men who were involved in committed, romantic relationships did not differ, suggesting that, at least for this sample, male pair bonding status is the more significant predictor of testosterone levels than is marital status.

The Effects of Remodeling on the Elastic Properties of Bone

SummaryCortical bone can be modeled as a complex hierarchical composite interrelating both structure and material properties on four levels of structural organization: molecular, ultrastructural, microscopic, and macroscopic. In young animals, the microstructural systems are long parallel lamellar units, plexiform bone, which in older or more mature animals converts by internal remodeling into multiple concentric lamellar units, secondary osteons, forming haversian bone. Ultrasonic wave propagation measurements performed on both plexiform and haversian bone clearly show a definitive relationship with microstructure; haversian bone can be described as a transversely symmetric material whereas plexiform bone appears to be orthotropic in nature. The anisotropy of the elastic constants are found to reflect the tissue symmetry; moreover, plexiform bone is stiffer and more rigid in all directions than is haversian bone. Similar experiments were performed on osteoporotic and osteopetrotic bone. While the results for osteoporotic bone are understandable in terms of the increased porosity, the results for the osteopetrotic bone are anomalous with respect to its density. Since Wolff, the remodeling of bone has been interpreted as a way of altering the mechanical properties to suit some need. For haversian remodeling from plexiform bone, the argument that adaptation occurs to optimize properties requires additional clarification since haversian bone appears to have inferior mechanical properties to plexiform bone.

Ovarian hormones and binge eating in bulimia nervosa

BACKGROUND Symptom fluctuation in bulimia nervosa (BN) is related to menstrual cycle phase. However, the relationship between bulimic symptoms and ovarian hormones (estrogens and progesterone) has not been examined directly in women with BN. METHOD Regularly menstruating women with DSM-IV BN (n=9) and regularly menstruating controls (n=8) collected hormone samples and recorded mood and bulimic symptoms daily for 35 consecutive days. Estradiol and progesterone were measured by radioimmunoassay. Within-subject analyses examined prospective longitudinal associations between changes in ovarian hormones and changes in binge frequency in women with BN. Analyses controlled for the possible influence of negative affect on binge frequency as well as the influence of progesterone when examining estradiol associations and the influence of estradiol when examining progesterone associations. Between-subject analyses examined whether women with BN were more likely to have disrupted hormonal profiles than controls. RESULTS Increases in binge eating were significantly associated with both decreases in estradiol and increases in progesterone in BN women with intact menstrual cycles. Although BN women were more likely to have disrupted hormone profiles than controls, this difference did not reach statistical significance, and mean estradiol and progesterone levels did not differ between bulimic and control groups. CONCLUSIONS The results are consistent with those from experimental animal studies and suggest that decreases in estradiol and increases in progesterone may contribute to increases in binge eating. Ovarian hormone function represents a promising candidate for unraveling the neurobiological mechanisms of binge eating.

Development of protocols for the application of salivary steroid analysis to field conditions

The simple and noninvasive nature of sample collection for salivary steroid assay makes this technique well suited for anthropological field studies of human reproduction function. In this study, a series of controlled experiments was done to investigate the effects of modifying common clinical sample collection and storage procedures for field use. Matched sets of samples were assayed for four steroids to test the effects of using plastic, rather than glass, collection tubes, of using a stimulant to aid collection, and of storing samples at ambient temperature rather than frozen.

Differential changes in steroid hormones before competition in bonobos and chimpanzees

A large body of research has demonstrated that variation in competitive behavior across species and individuals is linked to variation in physiology. In particular, rapid changes in testosterone and cortisol during competition differ according to an individuals or species’ psychological and behavioral responses to competition. This suggests that among pairs of species in which there are behavioral differences in competition, there should also be differences in the endocrine shifts surrounding competition. We tested this hypothesis by presenting humans’ closest living relatives, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), with a dyadic food competition and measuring their salivary testosterone and cortisol levels. Given that chimpanzees and bonobos differ markedly in their food-sharing behavior, we predicted that they would differ in their rapid endocrine shifts. We found that in both species, males showed an anticipatory decrease (relative to baseline) in steroids when placed with a partner in a situation in which the two individuals shared food, and an anticipatory increase when placed with a partner in a situation in which the dominant individual obtained more food. The species differed, however, in terms of which hormone was affected; in bonobo males the shifts occurred in cortisol, whereas in chimpanzee males the shifts occurred in testosterone. Thus, in anticipation of an identical competition, bonobo and chimpanzee males showed differential endocrine shifts, perhaps due to differences in perception of the situation, that is, viewing the event either as a stressor or a dominance contest. In turn, common selection pressures in human evolution may have acted on the psychology and the endocrinology of our competitive behavior.

Habitual physical activity and estradiol levels in women of reproductive age.

Variation in the risk of breast cancer observed among women and among populations may be explained by variation in lifetime exposure to estrogens. The suppressive effect of exercise on estradiol levels in women is well documented, but it is unknown whether habitual (i.e. typical daily) physical activity has a similar effect. Epidemiological data suggest that physical activity is one of the few modifiable factors capable of reducing the risk of breast cancer in women. We investigated whether variation in the amount of habitual activity corresponds to variation in estradiol levels in women of reproductive age. One hundred and thirty-nine regularly menstruating women 24–37 years of age collected daily saliva samples for one complete menstrual cycle and kept a daily log of physical activity. Saliva samples were analyzed for concentration of estradiol. We observed a negative relationship between habitual physical activity and salivary levels of estradiol. Mean estradiol was 21.1 pmol/l in the low, 17.9 pmol/l in the moderate and 16.6 pmol/l in the high activity group (all pairwise differences were statistically significant at P<0.009). A strong association exists between physical activity and levels of estradiol among women of reproductive age. A modern lifestyle, characterized by reduced physical activity, may therefore contribute to a rise in the levels of estradiol produced during menstrual cycles and thus to higher cumulative lifetime exposure to estradiol, resulting in a higher risk of breast cancer.

Body fat, energy balance and estradiol levels: a study based on hormonal profiles from complete menstrual cycles

BACKGROUND Female fecundity is regulated by nutritional status. Although widely cited, this hypothesis is not strongly supported by empirical data from non-obese, healthy women of reproductive age. METHODS Healthy, reproductive aged women (n = 141) from Southern Poland collected daily morning saliva samples for one complete menstrual cycle. Levels of 17-beta-estradiol were analyzed by radioimmunoassay. Anthropometric measurements, including body fat percentage, were taken randomly with respect to phase of the menstrual cycle. Energy balance was specified based on changes in body fat percentage from the beginning to the end of the observation period. RESULTS Women with very low and high body fat had significantly lower levels of E2 compared with women with low and average body fat. In women of very low to average body fat, a 10% increase in body fat was associated with a 5-7 pmol/l increase in estradiol levels. The association between fat percentage and E2 was even stronger in women with positive energy balance, who also showed significant differences between body fat groups in estradiol profiles across whole the menstrual cycle. No such relationship was found in women with negative energy balance. CONCLUSIONS In healthy women, we found a non-linear association between body fat and estradiol levels. Both very low and high body fat was associated with decreased estradiol levels. The relationship between estradiol and body fat was strongly influenced by womens energy balance.

Symptom fluctuation in bulimia nervosa: relation to menstrual-cycle phase and cortisol levels

BACKGROUND Individuals with bulimia nervosa report significant symptom fluctuation, and some studies have suggested a premenstrual exacerbation of binge frequency. The purpose of this study is to explore the hormonal correlates of symptom fluctuation in bulimia nervosa. METHOD For five consecutive weeks (one full menstrual cycle), eight women with bulimia nervosa and eight non-eating-disordered control women collected morning saliva samples and recorded several mood characteristics; the bulimic women also recorded binge and purge episodes. Subsequently, salivary cortisol and androgen levels were determined by radioimmunoassay. RESULTS Bulimic symptoms were exacerbated in both the mid-luteal and premenstrual phases, when compared with the follicular and ovulatory phases (F(3,21) = 3.76, P = 0.026; contrast analysis t(7) = 3.47, P < 0.01). Fluctuation in cortisol was closely correlated with fluctuation of bulimic symptoms, with elevatedcortisol secretion following symptom exacerbation (r(24) = 0.64, P = 0.001). CONCLUSIONS Bulimic symptom fluctuation appears to be related to two hormonal phenomena--phase of the menstrual cycle and cortisol secretion--with menstrual-cycle phase influencing bulimic symptom severity, and bulimic symptom severity effecting increases in cortisol secretion. Improved understanding of the hormonal causes and consequences of symptom fluctuation may lead to improved psychological and pharmacological treatments for bulimia nervosa.

Pooled energy budget and human life history

Human life history contains a series of paradoxes not easily explained by classical life history theory. Although overall reproductive output is higher than in related primates, juvenile growth is slower and age‐specific reproductive rates decline faster with age. A simple energetic model would predict that growth and reproductive rates should be positively correlated and that reproductive effort should not decelerate with age. The pattern of negative correlations in humans suggest the presence of trade‐offs among peak reproductive rate, childhood growth, and reproductive rate at older ages. To address this puzzle, we propose a synthesis of reproductive ecology and behavioral ecology focused on intra‐ and inter‐somatic energy transfers. This integration includes three concepts: the mother as final common pathway through which energy must pass to result in offspring; a distinction between direct and indirect reproductive effort, proposing the latter as a novel net energy allocation category relative to growth and direct reproductive effort; and a pooled energy budget representing the energetic contributions and withdrawals of all members of a breeding community. Individuals at all reproductive life stages are considered in light of their contributions to the pooled energy budget. Am. J. Hum. Biol., 2009.