Reactions to children's faces: Males are more affected by resemblance than females are, and so are their brains

The detection of genetic relatedness (i.e., kinship) affects the social, parental, and sexual behavior of many species. In humans, self-referent phenotype matching based on facial resemblance may indicate kinship, and it has been demonstrated that facial resemblance increases perceptions of trustworthiness and attractiveness [Proc. R. Soc. Lond., B Biol. Sci. 269 (2002) 1307–1312; Proc. R. Soc. Lond., B Biol. Sci. (in press)]. However, investigations of sex differences in reaction to facial resemblance have produced mixed results [Evol. Hum. Behav. 25 (2004) 142–154; Evol. Hum. Behav. 23 (2002) 159–166; Evol. Hum. Behav. 24 (2003) 81–87]. Here, we replicate the effects of Platek et al. [Evol. Hum. Behav. 23 (2002) 159–166] using high-resolution color morphing. We also extend these findings using functional magnetic resonance imaging (fMRI) to demonstrate a possible neural mechanism that may account for the observed sex difference. These data support the hypothesis that human males may use and favor facial resemblance as a paternity cue.     

Erythrocyte aging: a more than superficial resemblance to apoptosis?

In physiological circumstances, erythrocyte aging leads to binding of autologous IgG followed by recognition and removal through phagocytosis, mainly by Kupffer cells in the liver. This process is triggered by the appearance of a senescent erythrocyte-specific antigen. The functional and structural characteristics of senescent erythrocytes strongly suggest that this antigen originates on band 3, probably by calcium-induced proteolysis. Generation of vesicles enriched in denatured hemoglobin is an integral part of the erythrocyte aging process. These vesicles are also removed by Kupffer cells, with a major role for exposure of phosphatidylserine. Moreover, senescent erythrocyte-specific antigens are present on vesicles. Thus, vesicles and senescent erythrocytes may be recognized and removed through the same signals. These and other, recent data support the theory that erythrocyte aging is a form of apoptosis that is concentrated in the cell membrane, and provide the context for future studies on initiation and regulation of the erythrocyte aging process. Insight into the normal aging mechanism is essential for understanding the fate of erythrocytes in pathological circumstances and the survival of donor erythrocytes after transfusion.     

Facial resemblance of Japanese children to their parents

Facial resemblance between parents and their children could be an indicator of genetic relationship, and selective pressure could bias the resemblance of appearance. We assessed the degree of resemblance of 38 Japanese children (3–6 years old) to each of their parents using photographs. We asked nonrelatives to assess which of the parents each child resembled, manipulating indications of the sex of the children. Variance in the degree of resemblance between the children and their fathers was very large. Although the basic facial appearance of each parent can be reflected in each child with 50% probability, the children did not equally show the facial characteristics of each parent at the individual level. The indication of sex had no significant effect on the assessment of resemblance. On the other hand, a questionnaire given to the assessors revealed that, as children, they tended to be said to resemble the opposite-sex parent. This result indicates that alleged resemblance does not reflect an actual condition but rather might have cultural meaning. Electronic Publication     

Women's attractiveness judgments of self-resembling faces change across the menstrual cycle

Two lines of reasoning predict that women's preferences for people exhibiting cues to kinship will be lower in the follicular phase than in the luteal phase of the menstrual cycle. Women may avoid kinship cues during the follicular phase when they are most fertile due to the costs of inbreeding. Alternatively, women may seek kinship cues during the luteal phase as a byproduct of the benefits of associating with kin during pregnancy, which is also characterized by high progesterone. We find that preferences for facial resemblance, a putative kinship cue, follow this predicted pattern and are positively correlated with estimated progesterone levels based on cycle day. Neither estimated estrogen levels nor conception risk predicted preferences for self-resemblance, and the cyclic shift was stronger for preferences for female faces than male faces. These findings lead to the possibility that this cyclic change in preference for self-resemblance may be a byproduct of a hormonal mechanism for increasing affiliative behavior toward kin during pregnancy rather than a mechanism for preventing inbreeding during fertile periods.     

Facial attractiveness judgements reflect learning of parental age characteristics

Mate preferences are shaped by infant experience of parental characteristics in a wide variety of species. Similar processes in humans may lead to physical similarity between parents and mates, yet this possibility has received little attention. The age of parents is one salient physical characteristic that offspring may attend to. The current study used computer-graphic faces to examine how preferences for age in faces were influenced by parental age. We found that women born to 'old' parents (over 30) were less impressed by youth, and more attracted to age cues in male faces than women with 'young' parents (under 30). For men, preferences for female faces were influenced by their mother's age and not their father's age, but only for long-term relationships. These data indicate that judgements of facial attractiveness in humans reflect the learning of parental characteristics.     

The brain reaction to viewing faces of opposite- and same-sex romantic partners

We pursued our functional magnetic resonance imaging (fMRI) studies of the neural correlates of romantic love in 24 subjects, half of whom were female (6 heterosexual and 6 homosexual) and half male (6 heterosexual and 6 homosexual). We compared the pattern of activity produced in their brains when they viewed the faces of their loved partners with that produced when they viewed the faces of friends of the same sex to whom they were romantically indifferent. The pattern of activation and de-activation was very similar in the brains of males and females, and heterosexuals and homosexuals. We could therefore detect no difference in activation patterns between these groups.     

Facial attractiveness, symmetry and cues of good genes.

Cues of phenotypic condition should be among those used by women in their choice of mates. One marker of better phenotypic condition is thought to be symmetrical bilateral body and facial features. However, it is not clear whether women use symmetry as the primary cue in assessing the phenotypic quality of potential mates or whether symmetry is correlated with other facial markers affecting physical attractiveness. Using photographs of men's faces, for which facial symmetry had been measured, we found a relationship between women's attractiveness ratings of these faces and symmetry, but the subjects could not rate facial symmetry accurately. Moreover, the relationship between facial attractiveness and symmetry was still observed, even when symmetry cues were removed by presenting only the left or right half of faces. These results suggest that attractive features other than symmetry can be used to assess phenotypic condition. We identified one such cue, facial masculinity (cheek-bone prominence and a relatively longer lower face), which was related to both symmetry and full- and half-face attractiveness.     

Malaria infection increases attractiveness of humans to mosquitoes

Do malaria parasites enhance the attractiveness of humans to the parasite's vector? As such manipulation would have important implications for the epidemiology of the disease, the question has been debated for many years. To investigate the issue in a semi-natural situation, we assayed the attractiveness of 12 groups of three western Kenyan children to the main African malaria vector, the mosquito Anopheles gambiae. In each group, one child was uninfected, one was naturally infected with the asexual (non-infective) stage of Plasmodium falciparum, and one harboured the parasite's gametocytes (the stage transmissible to mosquitoes). The children harbouring gametocytes attracted about twice as many mosquitoes as the two other classes of children. In a second assay of the same children, when the parasites had been cleared with anti-malarial treatment, the attractiveness was similar between the three classes of children. In particular, the children who had previously harboured gametocytes, but had now cleared the parasite, were not more attractive than other children. This ruled out the possibility of a bias due to differential intrinsic attractiveness of the children to mosquitoes and strongly suggests that gametocytes increase the attractiveness of the children.     

Facial attractiveness ratings from video-clips and static images tell the same story

Most of what we know about what makes a face attractive and why we have the preferences we do is based on attractiveness ratings of static images of faces, usually photographs. However, several reports that such ratings fail to correlate significantly with ratings made to dynamic video clips, which provide richer samples of appearance, challenge the validity of this literature. Here, we tested the validity of attractiveness ratings made to static images, using a substantial sample of male faces. We found that these ratings agreed very strongly with ratings made to videos of these men, despite the presence of much more information in the videos (multiple views, neutral and smiling expressions and speech-related movements). Not surprisingly, given this high agreement, the components of video-attractiveness were also very similar to those reported previously for static-attractiveness. Specifically, averageness, symmetry and masculinity were all significant components of attractiveness rated from videos. Finally, regression analyses yielded very similar effects of attractiveness on success in obtaining sexual partners, whether attractiveness was rated from videos or static images. These results validate the widespread use of attractiveness ratings made to static images in evolutionary and social psychological research. We speculate that this validity may stem from our tendency to make rapid and robust judgements of attractiveness.     

Facial attractiveness and fertility in populations with low levels of modern birth control

Evolutionary models of human mate choice generally assume that physical attractiveness has evolved through sexual selection, i.e., it has been associated with higher mating opportunities and subsequent reproductive success across our evolutionary history. Here we investigate whether facial attractiveness is related to fertility in order to understand the extent to which selection can operate on attractive traits in modern populations. We used data from two populations where the prevalence of modern birth control methods is low and thus unlikely to disconnect mating opportunities from reproductive success: men and women from contemporary rural Senegal and men from the West Point Military Academy in the USA who graduated in 1950. We found that facial attractiveness negatively predicts age-specific reproduction in both sexes in Senegal and is independent from lifetime reproductive success in men from the USA. Overall, the results suggest that facial attractiveness is not under positive selection and raise questions about methodological approaches currently used to assess attractiveness.     

Removal of adult males from the rearing environment increases preference for same-sex partners in the zebra finch

The developmental processes producing preferences for opposite-sex mating partners are not well understood. Zebra finches, Taeniopygia guttata, are colonial and socially monogamous with biparental care. To determine whether the early social environment contributes to sexual partner preference, we removed adult males from breeding colonies when the oldest chicks were less than 1 week old (male-removal rearing) or left them in the breeding cage (control rearing). At independence, male-removal and control offspring were moved to unisex cages. As adults they were given two-choice tests with male versus female stimuli followed by group aviary tests. Male-removal subjects, unlike controls, did not prefer opposite-sex stimuli in the two-choice tests. Male-removal subjects were less likely than controls to successfully pair with opposite-sex birds in the group aviary tests; 38% of them paired with a same-sex bird. Thus early social experience may contribute to a critical component of mate choice, choosing the opposite sex, in this pair-bonding species. Copyright 2000 The Association for the Study of Animal Behaviour.     

PVN galanin increases fat storage and promotes obesity by causing muscle to utilize carbohydrate more than fat

To understand the function of the feeding-stimulatory peptide, galanin (GAL), in eating and body weight regulation, the present experiments tested the effects of both acute and chronic injections of this peptide into the paraventricular nucleus (PVN) of rats. With food absent during the test, acute injection of GAL (300 pmol/0.3 microl) significantly increased phosphofructokinase activity in muscle, suggesting enhanced capacity to metabolize carbohydrate, and reduced circulating glucose levels. It also decreased beta-hydroxyacyl-CoA dehydrogenase activity in muscle, indicating reduced fat oxidation, while increasing circulating non-esterified fatty acids (NEFA) and lipoprotein lipase activity in adipose tissue (aLPL). Chronic PVN injections of GAL (300 pmol/0.3 microl/injection) versus saline over 7-10 days significantly stimulated daily caloric intake and increased the weight of four dissected fat depots by 30-40%. These effects, accompanied by elevated levels of leptin, triglycerides, NEFA and aLPL activity, were evident only in rats on a diet with at least 35% fat. Thus, by favoring carbohydrate over fat metabolism in muscle and reversing hyperglycemia, PVN GAL may have a function in counteracting the metabolic disturbances induced by a high-fat diet. As a consequence of these actions, GAL can promote the partitioning of lipids away from oxidation in muscle towards storage in adipose tissue.     

Vitamin E supplementation increases the attractiveness of males' scent for female European green lizards

Background

In spite that chemoreception is important in sexual selection for many animals, such as reptiles, the mechanisms that confer reliability to chemical signals are relatively unknown. European green lizards (Lacerta viridis) have substantial amounts of α-tocopherol ( = vitamin E) in their femoral secretions. Because vitamin E is metabolically important and can only be attained from the diet, its secretion is assumed to be costly. However, its role in intraspecific communication is unknown.

Methodology/Principal Findings

Here, we experimentally show that male European green lizards that received a dietary supplement of vitamin E increased proportions of vitamin E in their femoral secretions. Furthermore, our experiments revealed that females preferred to use areas scent marked by males with experimentally increased vitamin E levels in their secretions. Finally, female preferences were stronger when vitamin E differences between a pair of males'' secretions were larger.

Conclusions/Significance

Our results demonstrate that female green lizards are able to discriminate between males based on the vitamin E content of the males'' femoral secretions. We suggest that the possible cost of allocating vitamin E to secretions, which might be dependent on male quality, may be a mechanism that confers reliability to scent marks of green lizards and allows their evolution as sexual signals.     

There's more to Krever's report than the blood issue -- much more

Although coverage of the recent release of the Krever commission''s findings concentrated almost solely on recommendations concerning the safety of the blood-supply system, lawyer Karen Capen says physicians can take many lessons from this exhaustive report that extend far beyond blood. She describes it as "must reading" for physicians and says their organizations should use it as a teaching tool.     

Experimentally reduced male attractiveness increases parental care in the pied flycatcher Ficedula hypoleuca

This study reports effects of experimental manipulations ofreproductive effort and the size of the male's white foreheadpatch (a secondary sexual trait), on provisioning rates, reproductivesuccess, and parental breeding dispersal distance in the piedflycatcher, Ficedula hypoleuca. Parents caring for enlargedbroods resulting from manipulated clutches provisioned nestsat higher rates than parents with reduced broods. Males witha reduced forehead patch fed their nestlings more in relationto males with an unmanipulated forehead patch, and their youngfledging with a longer tarsi. This suggests that males witha reduced attractiveness may perceive their own attractivenessand they devote more time available for parental effort giventheir poorer prospects in male contest competition and/or femaleattraction for extra-pair copulations. However, their femalesdid not alter their provisioning effort and this runs counterto both the differential allocation and the partner-compensationhypotheses. An artificial decrease in a male secondary sexualtrait led to a wider breeding dispersal distance between successiveyears.     

Vitamin D supplementation increases the attractiveness of males' scent for female Iberian rock lizards

Evolutionary theory proposes that signals used in sexual selection can only be stable if they are honest and condition dependent. However, despite the fact that chemical signals are used by many animals, empirical research has mainly focused on visual and acoustic signals. Vitamin D is an essential nutrient for lizards, but in some lizards its precursor (cholesta-5,7-dien-3-ol=provitamin D) is found in femoral gland secretions, which males use for scent marking and intraspecific communication. By allocating provitamin D to secretions, males might need to divert vitamin D from metabolism. This might be costly and condition dependent. We tested whether diet quality affected chemical signals of male Iberian rock lizards (Lacerta monticola) and its consequences for sexual selection. After experimental supplementation of dietary vitamin D, males increased the proportion of provitamin D in femoral secretions. Further experiments showed that females detected these changes in males' signals by chemosensory cues, and discriminated provitamin D, and changes in its concentration, from similar steroids (i.e. cholesterol) found in secretions. Moreover, females preferred areas scent marked by males with more provitamin D in their secretions. This mechanism would confer honesty to chemical signals of male lizards, and, thus, females may rely on it to select high-quality males. We suggest that the allocation of vitamins and other essential nutrients to either visual (e.g. carotenoids) or chemical ornaments might be the common basis of honest sexual displays in many animals.