From 2017... Sexual Differentiation of the Brain: A Fresh Look at Mode, Mechanisms, and Meaning

Margaret M. McCarthy, Geert J. De Vries, Nancy G. Forger, 5.01 - Sexual Differentiation of the Brain: A Fresh Look at Mode, Mechanisms, and Meaning, Editor(s): Donald W. Pfaff, Marian Joëls, Hormones, Brain and Behavior (Third Edition), Academic Press, 2017, Pages 3-32, https://doi.org/10.1016/B978-0-12-803592-4.00091-2

Abstract: This is an exciting time to study sex differences in the brain. Fifty-plus years of building on the foundations established by the organizational/activational hypothesis proposed by Phoenix and colleagues to explain steroid hormone action on the brain has provided an increasingly complex and nuanced view of how the brain develops differently in males and females. In this chapter we first discuss the things we know; there are sex differences in physiology and behavior, in susceptibility to diseases of the nervous system including mental health disorders, and in neuroanatomical and neurochemical measures. These sex differences depend on androgens, estrogens, and sometimes sex chromosomal complement (XX vs XY) acting during development as well as in adulthood, and yet the manifestation of these sex differences may be context dependent. There are four key cellular processes that could potentially underlie sexual differentiation of the brain: cell birth, cell death, cell migration, and cell differentiation, and we discuss the evidence for each in detail. Lastly, we review what we consider major emerging areas and unanswered questions in the field, including the function of sex differences, why they persist, and what they mean.

Keywords: Androgen; Anteroventral periventricular nucleus; Astrocyte; Bed nucleus of the stria terminalis; Bulbocavernosus; Cell death; Dendritic spine; Differentiation; Epigenetic; Estrogen; Hypothalamus; Partner preference; Preoptic area; Sex chromosome; Sex difference; Spinal cord; Vasopressin

5.01.4.5 Is Partner Preference Sexually Dimorphic?

Sexual orientation, also referred to as sexual partner preference,

is defined by the sex of the individuals that are arousing or attractive

to the reference individual, whether it be an individual of the

opposite sex (heterosexual), the same sex (homosexual), or both

sexes (bisexual). The estimated frequency of homosexuality in

humans ranges from 2% to 10%, suggesting that the large

majority of males are sexually oriented toward females and the

majority of females are sexually oriented towardmales. The overwhelming

prevalence of one sex preferring the other is a constant

across all vertebrate species, as would quite naturally be expected

from the point of view of reproductive success. Nonetheless,

what draws the majority of attention is the much less frequent

phenotype of same-sex preference. Notably, the biological basis

of sexual orientation is a matter of impassioned debate only

when it involves discussion of the etiology of homosexuality.

Few seem to question whether opposite-sex orientation is biological.

But actually we understand little about opposite-sex

attraction, and it can be argued that understanding the biological

basis of same-sex orientation would be greatly advanced by

understanding opposite-sex orientation. Thus, a fundamental

question is whether sexual orientation per se is sexually

differentiated.

The answer to this may depend on how you pose the question.

If we state that the majority of males prefer females as

sexual partners and the majority of females prefer males, then

this sounds like a profoundly sexually dimorphic and presumably

differentiated response. Antecedent to this view would be

the assumption that distinct biological processes drive the

neural substrate of partner preference to either a male bias or

a female bias. The existence of distinct processes for a male preference

versus a female preference provides a ready explanation

for why some females prefer other females, some males prefer

males, and why some individuals have no preference.

However, if we take the view that the majority of animals prefer

the opposite sex as partners, then there is no sex difference as

the same drive exists in males and females but it is manifest

differently as a function of one’s own sex. This means that

a component of the neural response is computation of one’s

own sex, which then determines the response to others’ sex.

Given the intensity and early onset of both internal and

external influences of sex on brain development, this is not

outside the realm of possibility. In humans, we are unlikely

to ever be able to definitively separate the impact of nature

from nurture, and our best alternative is the study of naturally

occurring or experimentally manipulated variation in sexual

preference in animals.

The current state of the art of partner preference research is

found on several fronts. These include studies of the programming

effects of gonadal steroids and early experience on partner

preference, the neuroanatomical loci controlling partner preference,

and the study of naturally occurring variation in partner

preference in animal models. Consistent evidence supports

the view that partner preference is organized by gonadal

steroids, such that perinatal androgens, with aromatization to

estrogens in rodents, direct the formation of preference for

a female sexual partner (Brand et al., 1991; Vega Matuszczyk

et al., 1988). In many mammals, odors are the primary signal

indicating sex. Preference can be assessed by determining the

amount of time a test subject prefers to spend with male versus

female stimulus animals or by the amount of time spent investigating

odors generated by stimulus animals. Male- versus

female-specific odors can induce a differential brain response

in the same animal, and likewise, animals of opposite sex

will respond to the same odor differently (Bakker et al.,

1996; Woodley and Baum, 2004). The latter speaks to the

sexual differentiation of partner preference and suggests that

the olfactory system may be the initiation point for subsequent

behavioral responses. In many species, if olfaction is blocked,

there is no partner preference to measure.

Olfaction is important to humans as well, but visual stimuli

are far more potent and the arousal potential of same-sex versus

opposite-sex images depends on the partner preference of the

observer (see for review Baum, 2006). Zebra finches are also

heavily dependent upon vision for expressing partner preference,

and steroids influence partner preference in this species as well

(Adkins-Regan and Leung, 2006). The effect is context dependent,

however, because early experience, i.e., being raised in an

environment with a skewed sex ratio, can also strongly influence

adult partner preference in zebra finches.

The neuroanatomical substrate of partner preference begins

with that portion of the brain detecting and decoding the

sex-specific sensory signals originating from the stimulus

animal, be they olfactory, visual, or auditory. But from there,

all signals appear to converge on the POA, and in particular

an SDN within the POA (see Baum, 2006). An SDN is present

in the POA not only in rats, but also in sheep, gerbils, ferrets,

hamsters, and humans. Lesions of the SDN and its surround

in rats and ferrets either eliminate or reverse sexual preference

(for review, see Baum, 2006). In humans, the third interstitial

nucleus of the hypothalamus (INAH3) may be homologous

to the SDN-POA of rats and is larger in men than women

(Allen et al., 1989). Levay (1991) found that INAH3 is

smaller in homosexual men than in heterosexual men, and

a second study found a mean difference in the same direction

that did not, however, reach statistical significance (Byne

et al., 2001). Thus, the size of INAH3 may be a marker of

partner preference in men, although this conclusion is not

without its detractors.

Another approach is the use of biomarkers to determine if

an individual was exposed to an endocrine environment

in utero that varies from the norm for that sex. These biomarkers

include long bone length, hand digit ratio, and the detection of

small noises made by the inner ear. In general, these studies

support the conclusion that the prenatal hormonal milieu

contributes to the propensity to show same-sex orientation

(Balthazart, 2016). But in many human and animal studies,

a major and unavoidable confound is either the use of surgical

manipulations, such as lesions, or the health status of the

affected individuals, such as the number of HIV-infected

subjects in the homosexual group in human studies. Neither

of these criticisms applies to the study of a naturally occurring

variant of homosexuality, the male-preferring domestic ram.

In at least two different study populations, approximately 8%

of rams prefer to mount other male rams. The frequency of

the phenotype is similar to that observed in humans, and there

are no clear external markers of male-preferring rams. Analyses

of the brain reveal that the SDN of male-preferring rams is

smaller than that of rams that prefer ewes, and it contains fewer

aromatase-expressing neurons. This suggests reduced neuronal

exposure to estradiol developmentally and in adulthood may

be a critical variable in the establishment of same-sex preference

in this species (Roselli et al., 2004).

Thus, on balance, we can conclude that partner preference

is sexually differentiated and that there is an important role for

gonadal steroid exposure in the organization of partner preference,

but early experience may also be important. The primary

detection of the sensory stimulus emanating from a potential

partner is a critical initiating step but the integration and

response to the stimulus appear to be encoded within the

POA. While these are important advances, there remains

much to be learned. Work on the genetics of partner preference

generated a great deal of interest in the early 1990s

(Hammer et al., 1993), but there has been little progress on

that front. There is a continuing interest in the role of birth

order and correlations with handedness, particularly for

male homosexuality, and the proposal of the maternal

immune hypothesis (Blanchard et al., 2006). But again, we

know far less than we should. Moreover, the preponderance

of information is weighted toward understanding male, as

opposed to female partner preferences, although this may be

defensible given the health implications for male versus

female homosexuality. Regardless, progress on both is likely

to remain slow given the paucity of researchers and resources

currently dedicated to this topic.

5.01.4.6 Is the Human Brain Sexual Differentiated?

To some an affirmative answer to this question is self-evident:

how could the human brain not be subject to the same process

that occurs in the majority if not all other mammals as well as

many birds, reptiles, and amphibians? Even invertebrates have

brains that differ in males and females. But others argue, ‘not so

fast, humans are exceptional in many ways.’ We are the only

species with complex computational abilities and a sophisticated

language that includes generation of an historical record.

We also have rich cultural and societal rituals and expectations

that include prescriptions of the appropriate behavior for boys

and girls, men and women. These rules and expectations are

imposed on children even before they are born with the choice

of a gender-typical name and continue with modes of dress and

even the manner in which adults interact with an infant of one

sex versus the other. Thus as we have mentioned many times in

this chapter, it is impossible to parse out the influence of environment

and experience from biology when considering the

brain and behavior of humans. Nonetheless, it is worth a try.

One powerful approach is the study of children at a young

age. While the influence of environment and experience cannot

be eliminated, it is at least lessened compared to that of a fullgrown

adult. Toy choice reflects an interest in different types of

objects, and this varies on average between boys and girls. The

data are messy, with many boys willing to play with girls’ toys

on occasion, and vice versa. One of the strongest influences is

whether a child has a sibling of the opposite sex, demonstrating

the importance both of exposure and of modeling the behavior

of other children. Nonetheless, on average, boys spend more

time with certain types of toys and girls with others. Melissa

Hines has spent most of her career studying this phenomenon

and whether prenatal exposure to androgens in girls can influence

toy choice. She and others have consistently found that

androgen-exposed girls shift their toy preference to that of

boys (reviewed in Hines, 2006). So does this mean there is

a ‘toy’ nucleus in the brain that directs boys to like trucks and

girls to like dolls? That seems unlikely. Hines and colleagues

recently added a new dimension to the sexual differentiation

of play with the observation that girls prefer to mimic the

behavior of other girls or women and that it is this aspect of

their brain development that is influenced by hormones, not

the desire to play with a particular object or in a particular

way (Hines et al., 2016). In girls exposed to androgens in utero,

the desire to mimic other females is lost, and for reasons not

well understood, their preference shifts to toys normally

preferred by boys.

The work of Hines and others speaks to the behavior of

humans, but, as noted above, brain and behavior are not

always closely aligned. Many neuroanatomical sex differences

have been reported in the human brain, but the majority of

these relied on postmortem tissue. Because of this, the majority

also involved the brains of adults although one remarkable

study looked at a nucleus in the hypothalamus from many

different individuals ranging from birth to old age and found

a sex difference that did not appear until late adolescence

and then waned again in older adults (Swaab et al., 2003).

More recently, researchers have taken advantage of noninvasive

imaging techniques that allow for longitudinal analyses of the

same individual as they mature. The magnitude and direction

of sex differences varies with the mode of data acquisition and

analyses (i.e., correcting for total brain volume or not), but

differences in the developmental trajectory of the peak of

cortical gray matter are reliably found and modulated by

androgen receptor allelic variation as well as androgen levels.

White matter increases more rapidly in male brains as development

proceeds and combined with differences in gray matter

amplify the magnitude of sex differences across the life span

(reviewed in Giedd et al., 2012).

More recently advances in imaging have allowed formeasurement

of functional connectivity. Images from almost 1000

humans revealed a profound sex difference in the ‘connectome,’

with females showing strong interhemispheric connectivity and

males the opposite, strong intrahemispheric connections

(Ingalhalikar et al., 2014). The authors interpreted their findings

as supportive of the view that females engage multiple tasks at

once and are highly social whilemales are focused systematizers.

This stereotypical view generated a firestorm of criticism. In

response the authors went on to use a computerized battery of

neurocognitive tasks in combination with imaging and largely

supported their original conclusions (Tunc et al., 2016), but the

controversy here is certainly not resolved.

On the opposite end of the spectrum and equally controversial

was a recent report that reexamined several studies

involving imaging and gender-typical activities. Here the

authors concluded that there was no clear predictability of

sex based on the mean responses (Joel et al., 2015). Instead,

they concluded, every brain is a mosaic of male-like, femalelike,

and neutral features, and therefore there is no such thing

as a ‘male brain’ or a ‘female brain.’ In some ways this conclusion

is intuitively obvious and consistent with the high degree

of regionally specific mechanisms establishing sex differences

in the brain as determined in rodent models. But the finding

was largely misinterpreted by the lay media as demonstrating

there are no sex differences in the brain, which was not the

case even in the Joel et al. study.

This serves as a fitting conclusion to our long treatise on the

modes, mechanisms, and meanings of sex differences in the

brain as it so aptly demonstrates how much we still have to

learn. In some ways, the topic of sex differences in the brain

remains as controversial today as when the first reports were

made in the late 1960s early 1970s. With the changing policies

at major granting agencies, there is likely to be more, not fewer

reports of brain and behavior sex differences. This makes even

more salient the admonishment that scientists bear the burden

of assuring their work is not used or interpreted inappropriately

(Maney, 2016). It is essential that we ‘get it right’ as the implications

of sex differences research reach far beyond the laboratory

to medical, educational, and public health policies that

impact the daily lives of all members of society.

Evidence of cross-cultural variation in assessments of age, and even more of attractiveness, and health, indicating plasticity in perception of female facial appearance across cultures

Cross-cultural perception of female facial appearance: A multi-ethnic and multi-centre study. Rainer Voegeli, Rotraut Schoop, Elodie Prestat-Marquis, Anthony V. Rawlings, Todd K. Shackelford, Bernhard Fink. PLoS One, January 22, 2021. https://doi.org/10.1371/journal.pone.0245998

h/t David Schmitt (20) David Schmitt on Twitter: ""cross-cultural variation in assessments of age, even more of attractiveness/health, indicating plasticity in perception of female facial appearance across cultures, though the decline in attractiveness and health assessments with age is universally found" https://t.co/ZZOWx0oReV" / Twitter

Abstract: Humans extract and use information from the face in assessments of physical appearance. Previous research indicates high agreement about facial attractiveness within and between cultures. However, the use of a narrow age range for facial stimuli, limitations due to unidirectional cross-cultural comparisons, and technical challenges have prevented definitive conclusions about the universality of face perception. In the present study, we imaged the faces of women aged 20 to 69 years in five locations (China, France, India, Japan, and South Africa) and secured age, attractiveness, and health assessments on continuous scales (0–100) from female and male raters (20–66 years) within and across ethnicity. In total, 180 images (36 of each ethnicity) were assessed by 600 raters (120 of each ethnicity), recruited in study centres in the five locations. Linear mixed model analysis revealed main and interaction effects of assessor ethnicity, assessor gender, and photographed participant (“face”) ethnicity on age, attractiveness, and health assessments. Thus, differences in judgments of female facial appearance depend on the ethnicity of the photographed person, the ethnicity of the assessor, and whether the assessor is female or male. Facial age assessments correlated negatively with attractiveness and health assessments. Collectively, these findings provide evidence of cross-cultural variation in assessments of age, and even more of attractiveness, and health, indicating plasticity in perception of female facial appearance across cultures, although the decline in attractiveness and health assessments with age is universally found.

Discussion

Previous research suggested strong agreement in attractiveness assessments, both within and across ethnicities [23, 40, 50], especially for female attractiveness [29, 51, 52]. The present study used a simultaneous multi-centre, multi-ethnic approach to secure assessments of female facial age, attractiveness, and health and identified both similarities and differences in assessments across ethnicities. Perhaps most importantly, there were (three-way) interaction effects of assessor ethnicity and gender, and participant (“face”) ethnicity for attractiveness and health (but not for age). This suggests that differences in female facial attractiveness and health judgments depend on who judges the face (i.e. assessor ethnicity), which face is assessed (i.e. target ethnicity), and whether the assessor is female or male. There is stronger agreement in facial age assessments than in attractiveness and health assessments.

Intra-class correlations (ICCs) corroborate the findings of diversity in cross-cultural face assessments; the ICC for age assessments was higher than for attractiveness and health assessments, suggesting greater agreement for the former than the latter assessments. Inter-correlations of female facial age, attractiveness, and health assessments were large and in the direction predicted by evolutionary approaches to female appearance (see for review Grammer et al. [9], Rhodes [4], and Thornhill and Gangestad [12]), suggesting a strong relationship of attractiveness with health, and a decline in these qualities with age [3, 17, 53]. Collectively, the findings of the present study suggest greater cross-cultural variation in assessments of female facial appearance than indicated in previous research, especially in attractiveness and health assessments.

Recent research reported disagreement among individual facial attractiveness judgements, highlighting the importance of determining how these preferences vary among individuals [54, 55]. Perhaps most relevant for cross-cultural comparisons is the assumed importance of certain facial characteristics in a given society as derived from the study of another society. Facial characteristics investigated in previous studies (e.g., symmetry, averageness, sex-typical features) may not contribute substantially to judgements of facial attractiveness [56–58] or health [59], but even if they do, the contribution of these features may vary across societies depending on environmental conditions [60, 61] or sociocultural settings [62, 63]. Zhang et al. [57] in a data-driven (as opposed to theory-driven) approach detected cross-cultural differences in face preferences not apparent in studies using theory-driven approaches, leading to the conclusion that Chinese and British “White” participants used face information in different ways (i.e. they focused on different features) (see also Kleisner et al. [64]). Similar conclusions were derived from the findings of eye-movement patterns of Western and East Asian participants, suggesting that cultural background shapes visual environment affordance [35]. Coetzee et al. [65] investigated attractiveness assessments of White Scottish and Black S. African students for own- and other ethnicity faces. Black S. African raters relied more heavily on colour cues in their assessments of Black African female attractiveness, whereas White Scottish judges relied more heavily on shape cues in their assessments. The researchers concluded that although there was evidence for the universality of facial attractiveness assessments, the ethnicity of the target face moderated this agreement, i.e. agreement on European faces was higher than on African faces (possibly due to a difference in familiarity with other-ethnicity faces).

In the present study, the female participants (imaged women) were recruited in major cities. We might assume that contact with other ethnicities is considerable. Coetzee et al. [65] stated for S. Africans, for example, there is variation across samples in terms of familiarity with other ethnicities’ facial appearance. However, this alone cannot explain the variation in the facial assessments across ethnicities in our findings. The patterns of age assessments are similar across ethnicities, for both face ethnicity and assessor ethnicity. If assessors of one ethnicity were unable to accurately assess facial appearance of other ethnicities because of unfamiliarity with the variation in morphology, the patterns of age assessments across ethnicities should be more diverse than was the case (although there were differences in mean age assessments). Age-related changes in facial morphology (in terms of shape) and visible skin condition both play a role in age assessments. Yet the relative contribution of these features to age perception may be different across ethnicities depending, for example, on the visibility of skin colouration cues. In lightly pigmented skin, unevenness may be more detectable than in darkly pigmented skin. In the present study, our focus was on the investigation of cross-cultural differences (or similarities) in perceptions of female facial appearance. Thus, we did not quantify facial morphology and/or skin condition. As such, the possibility of cross-cultural variation in the relative importance of these components for age assessments remains to be investigated.

Attractiveness and health assessments showed greater variation across ethnicities, with some large differences associated with face and assessor ethnicity, in addition to gender differences. Perhaps most conspicuous in the pattern of cross-cultural variation in facial attractiveness and health is the low assessments of S. African (and Indian) women (and the absence of a gender difference) made by Indian assessors. This may reflect the influence of socio-cultural factors, namely “colourism” (i.e. a preference for lighter skin colour, possibly dating to colonialism) [66] (but see Wagatsuma, 1967 [67]), on face perception, as darkly pigmented skin in India is perceived negatively, partially due to the hierarchical caste system [68, 69]. Similar “colourism” has been reported for S. Africa where lighter-skinned migrants have been treated more positively than darker-skinned migrants [70]. In the present study, S. African assessors judged French faces lowest and Indian faces highest on attractiveness.

Many additional factors might contribute to cross-cultural differences in attractiveness assessments, including environmental settings [29, 71–73] and measures of national health [28, 39], along with variation within- and between assessors (e.g., hormonal fluctuations), which have been reviewed elsewhere [4, 12, 30, 74, 75] (but see Jones et al. and Marcinkowska et al. [76, 77]). There is consensus that certain facial cues relate to female age and health, both of which correlate with female fecundity and reproductive potential [9, 13, 15, 78]. From an evolutionary perspective, one might assume that these relationships are found universally, and the evidence from industrialized and pre-industrialized societies suggests that this is the case. However, this universality does not preclude variation in the strength of associations across ethnicities. Our findings of cross-cultural variation in perceptions of female facial appearance do not challenge the evidence that certain facial cues provide information about an individual’s mating-related quality. We document negative correlations between age and attractiveness/health, and a positive correlation between attractiveness and health for every combination of face ethnicity and assessor ethnicity. The relative size of effects and the mean assessments may differ across cultures because of differences in environmental conditions, socio-cultural factors, and other variables that contribute to individual differences (see for a review, Pisanski and Feinberg [79]). Nevertheless, the biological blueprint nature uses to convey certain information about an individual’s quality may be the same for all humans [9].

Many studies investigating human physical attractiveness include a statement on the stability of attractiveness ratings across ethnicities (“strong cross-cultural agreement”). However, there is concern about the validity of this statement [54, 55, 80, 81]. The findings of the present study corroborate the presence of differences in the assessment of female facial appearance, depending on the ethnicity of the face and the ethnicity and gender of the assessor. These cross-cultural differences in face assessments are evident especially in attractiveness and health ratings, at least in samples of industrialized and industrializing countries. Previous research reporting differences in face preferences of industrialized vs. pre-industrialized societies [82, 83] suggested that visual experience with facial cues may account for the effect (but see Danel et al. [80]). We suggest that visual experience with faces of other ethnicities alone cannot explain our findings. Rather, our findings may be explained through a combination of ethnocentrism [84, 85] and other effects that emerge from different socio-cultural settings. However, the variation in patterns of assessments of female facial appearance may also reflect evolved preferences expressed in response to environmental settings that contributed to the development of plasticity in the perception of female facial appearance across cultures. Future studies should i) quantify cross-cultural variation in facial morphology and visual skin condition, and disentangle the relative impact of these components on face ratings, and ii) consider the influence of ethnocentrism and stereotyping in cross-cultural (facial) assessment, in addition to effects motivated by human sexual psychology. For example, face research has successfully applied geometric morphometrics in the assessment of facial shape variation in samples of industrialized and non-industrialized societies in relation to physical capacity and/or perception (e.g., Butovskaya et al., Fink et al., Schaefer et al., and Kleisner et al. [86–89]). Similarly, objective measures of skin color and the evenness of skin tone correlate with assessments of facial age, attractiveness, and health [90, 91]. The application of these technologies in the current multi-ethnic and multi-centre study would take the study findings to the next level by investigating features that predict cross-cultural variation in face assessments.

Although the high level of standardization of facial imaging and assessment protocols is a strength of the current study, we contend that it could be realized only in cooperation with local study centres in major cities. The collection of similar stimuli and information from members of small-scale societies in anthropological fieldwork remains challenging. Therefore, evidence from studies that have investigated face assessments cross-culturally should be considered with caution regarding the comparability of study findings. This includes questions about influences from (Western) media shaped face perception, which can be assumed to be present in all population samples of the current study. France, for example, is a global leader in the cosmetics business, and French cosmetic products are highly regarded especially in China and Japan, possibly leading to stereotypic and higher assessments of French women compared to women of other ethnicities. We suggest that studies investigating cross-cultural agreement in face perception and the reasons for geographical variation need to quantify socio-cultural stereotypes (e.g., Choi et al. [92] in inter-population perception in addition to securing objective measures of biological variation in facial appearance.

Equality for (almost) all: Egalitarian advocacy predicts lower endorsement of sexism and racism, but not ageism

Martin, A. E., & North, M. S. (2021). Equality for (almost) all: Egalitarian advocacy predicts lower endorsement of sexism and racism, but not ageism. Journal of Personality and Social Psychology, Jan 2021. https://doi.org/10.1037/pspi0000262

h/t David Schmitt (20) David Schmitt on Twitter: ""egalitarian advocacy predicts greater likelihood to support “Succession”-based ageism, which prescribes that older adults step aside to free up coveted opportunities...equality for all may only mean equality for some" https://t.co/PTYtfpLNKF" / Twitter

Abstract: Past research has assumed that social egalitarians reject group-based hierarchies and advocate for equal treatment of all groups. However, contrary to popular belief, we argue that egalitarian advocacy predicts greater likelihood to support “Succession”-based ageism, which prescribes that older adults step aside to free up coveted opportunities (e.g., by retiring). Although facing their own forms of discrimination, older individuals are perceived as blocking younger people, and other unrepresented groups, from opportunities—that in turn, motivates egalitarian advocates to actively discriminate against older adults. In 9 separate studies (N = 3,277), we demonstrate that egalitarian advocates endorse less prejudice toward, and show more support for, women and racial minorities, but harbor more prejudice toward (Studies 1 and 2), and show less advocacy for (Studies 3–6), older individuals. We demonstrate downstream consequences of this effect, such as support for, and resource allocation to, diversity initiatives (Studies 3–6). Further, we isolate perceived opportunity blocking as a critical mediator, demonstrating that egalitarian advocates believe that older individuals actively obstruct more deserving groups from receiving necessary resources and support to get ahead (Studies 4–6). Finally, we explore the intersectional nature of this effect (Study 7). Together this research suggests that when it comes to egalitarianism, equality for all may only mean equality for some.

Investors who trade in months of less attention are more experienced, engage more in complex trading, have less of a home bias tendency, are wealthier, & have a higher income than those who trade during the highest attention-grabbing months

Net Buyers of Attention-Grabbing Stocks? Who Exactly Are They? Liron Reiter Gavish, Mahmoud Qadan & Joseph Yagil. Journal of Behavioral Finance, Volume 22, 2021 - Issue 1, Pages 26-45, Feb 6 2020. https://doi.org/10.1080/15427560.2020.1716360

Rolf Degen's take: (20) Rolf Degen on Twitter: "Attention-grabbing stocks light inexperienced traders' fire. https://t.co/9KTgBj5Szs https://t.co/JtWRVWP64v"

Abstract: The literature has established that retail investors are “net buyers” of attention-grabbing stocks. In this study, the authors utilize a unique dataset of actual information about 290,000 household investment accounts and track their “net buying” decisions with a focus on their economic and demographic characteristics. Unlike previous research, the authors focus not only on net buyers of attention-grabbing stocks, but also on net sellers of such stocks. They find that factors such as financial experience, wealth, consulting with advisors, and other individual characteristics, indicative of investors’ sophistication, account for the differences in the net buying decision. Specifically, the authors find that more trading experience and a lower tendency for home bias are associated with net selling during months when stocks attract a great deal of attention, and with net buying during months when they are paid less attention. The authors document that investors who trade in months of less attention are more experienced, engage more in complex trading, have less of a home bias tendency, are wealthier, and have a higher income than those who trade during the highest attention-grabbing months. Finally, the use of financial advice varies not only between households, but also between months in which stocks receive a great deal or little attention.

Keywords: Household financeInvestor attentionInvestor literacyInvestor sophisticationTrading bias

Our findings suggest that lower male pitch and formants may be valid cues of some components of fighting ability in men

Low fundamental and formant frequencies predict fighting ability among male mixed martial arts fighters. Toe Aung, Stefan Goetz, John Adams, Clint McKenna, Catherine Hess, Stiven Roytman, Joey T. Cheng, Samuele Zilioli & David Puts. Scientific Reports volume 11, Article number: 905 (2021). Jan 13 2021. https://www.nature.com/articles/s41598-020-79408-6

h/t David Schmitt (20) David Schmitt on Twitter: ""lower male pitch and formants may be valid cues of some components of fighting ability in men" https://t.co/4dRGZT7XyH"

Abstract: Human voice pitch is highly sexually dimorphic and eminently quantifiable, making it an ideal phenotype for studying the influence of sexual selection. In both traditional and industrial populations, lower pitch in men predicts mating success, reproductive success, and social status and shapes social perceptions, especially those related to physical formidability. Due to practical and ethical constraints however, scant evidence tests the central question of whether male voice pitch and other acoustic measures indicate actual fighting ability in humans. To address this, we examined pitch, pitch variability, and formant position of 475 mixed martial arts (MMA) fighters from an elite fighting league, with each fighter’s acoustic measures assessed from multiple voice recordings extracted from audio or video interviews available online (YouTube, Google Video, podcasts), totaling 1312 voice recording samples. In four regression models each predicting a separate measure of fighting ability (win percentages, number of fights, Elo ratings, and retirement status), no acoustic measure significantly predicted fighting ability above and beyond covariates. However, after fight statistics, fight history, height, weight, and age were used to extract underlying dimensions of fighting ability via factor analysis, pitch and formant position negatively predicted “Fighting Experience” and “Size” factor scores in a multivariate regression model, explaining 3–8% of the variance. Our findings suggest that lower male pitch and formants may be valid cues of some components of fighting ability in men.

Discussion

Sexual dimorphism in fo likely arose in the common ancestor of the catarrhine primates after their divergence from the New World monkeys6 approximately 43.5mya44 and appears to have been subsequently elaborated or reduced depending on the form and degree of male mating competition6. Relatively low male fo may have evolved as a means of exaggerating the appearance of size to same-sex competitors and/or potential mates6,18, but there is considerable debate regarding whether male fo is purely deceptive20,21,45 or provides any reliable information about formidability in men11,17,33.

To shed light on this debate, we investigated whether fo is associated with fighting ability among a large sample of male MMA fighters. Results of our pre-registered analyses were generally in the direction of lower fo predicting greater fighting ability but were mixed in terms of statistical significance. When we addressed the limitations of these analyses by creating more precise measures of fighting ability and accounting for the contributions of the distinct dimensions revealed through principal axis factoring, we found that lower fo was associated with greater fighting ability in all analyses. In the statistical model that most precisely measured fighting ability by including principal axis factors related to fighting experience, fighting success, and body size, fo predicted fighting ability generally and specifically components of fighting ability related to experience and size, but not within-weight class fighting success. Overall, these results suggest that low fo is an honest cue of formidability in men (Table 3).

Table 3 Component axis analysis for measures related to fighting ability.

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Effect sizes were small, however. Even when fighting ability was measured most precisely, fo explained only 1–3% of the variance (Table 4). On the one hand, the strength of these associations accords with theoretical predictions derived from the fact that signaling is multimodal and multi-component17. On the other hand, it is important to emphasize that relationships between fo and fighting success among MMA fighters may underestimate those in the general population due to range restriction on fighting ability. Among elephant seals, the body length of males who occupied the center of harems correlated with neither maximum harem size nor tenure length on the beach during the breeding season46. However, when all males were analyzed together, including those that were peripheral to or outside of the harem, male body length explained 17% of the variation in tenure length on the beach. The degree to which fo correlates with fighting ability in the general population has yet to be tested for obvious ethical reasons.

Table 4 Results of a multi-variate regression model.

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Voice pitch and other acoustic variables are modulated across social contexts, including those related to perceived fighting ability relative to a competitor13,47, relative dominance and prestige48, authority36, current aggressive intent49, emergent rank16, and volitional exaggeration50,51. On the one hand, if voice pitch is modulated in relation to self-perceived relative formidability and status, as this prior research indicates, then it is possible that any voice modulation of fighters during interviews could have strengthened relationships between acoustic parameters and measures of fighting ability in the present study. On the other hand, if voice modulation is less patterned or less dependent upon perceived relative formidability, then this would introduce noise in measuring individual differences in voices, which would tend to weaken relationships between acoustic parameters and true fighting ability. In these data based on naturalistic observations, although we cannot rule out that some fighters may have modulated their voice pitch or other vocal parameters during interviews to sound stronger, we sought to strengthen our measures of individual differences in acoustic traits by sampling across multiple interview occasions. Indeed, we found that acoustic measures were consistent across fighters, even between pre- and post-fight conditions in the subset of our sample for which this information was available (see Supplemental Procedures for details), and we attempted to capture more stable individual acoustic differences rather than measurements specific to particular recording conditions by using the unbiased linear estimates across recordings for each fighter in all analyses.

Only one previous study of which we are aware28 examined links between fighting success and fo or other acoustic measures and found that acoustic measures did not predict win percentage among male MMA fighters. Likewise, in our bivariate correlation analysis, we did not find a significant relationship between win percentage and vocal fo (Table 1), although lower fo predicted a greater number of UFC matches. Our ability in subsequent analyses to detect relationships between fo and fighting ability where a previous study did not28 may have been due in part to our examination of a larger sample of fighters (474 vs. 29), along with longer total voice samples from each fighter (approximately 85 s vs. 8 s).

Our use of unstandardized, spontaneous speech samples also offered enhanced ecological validity47, and although this approach adds noise to the measurement of individual differences in acoustic parameters, previous research shows strong correspondence across speech and/or vocalization types for both fundamental52 and formant10 frequencies. Moreover, the best linear unbiased composite estimates of acoustic measures from multiple voice recordings of each fighter, along with relatively long (> 85 s) average total speech samples from individual fighters, provided reliable estimates of individual differences in acoustic features.

Perhaps most importantly, we extracted component variables via factor analysis to produce more comprehensive measures of fighting ability than can be offered by individual measures such as Elo rating or win percentage. For example, win percentage alone is an imperfect indicator of fighting success because fighters with fewer fights and losses can achieve higher win rates53,54 and because win percentage does not account for the strength of opponents as Elo ratings do. Our factor analysis addressed such limitations and produced three unique components of fighting ability, which we termed Fighting Experience, Fighting Success, and Size. Fighting Experience reflects the component of flighting ability most strongly related to total number of fights but also strongly related to years active in the UFC and age. Given that Elo ratings also loaded positively onto this component, it may represent the component of fighting skill attributable to experience. Fighting Success reflects a component of fighting ability related to a history of winning in one’s weight class that is relatively unrelated to experience or size, perhaps tapping characteristics such as speed, agility, and strength for one’s size. The extracted Size factor reflects the component of fighting ability related to height and weight. Larger size is generally associated with lower fo across mammals55 and is a major determinant of dominance and social status across species56,57,58,59,60. Physical size is such a strong determinant of outcomes in combat sports such as wrestling, boxing, and martial arts that weight classes are needed to prevent dangerous lopsided contests, and fighters are willing to sacrifice energy and hydration by cutting weight to fight smaller opponents. Parallel to findings in previous studies32,61, fighters’ fo predicted their height and weight, as well as their Size factor scores.

Our orthogonal factor analysis extracted independent components of fighting ability, maximizing the variance among items and facilitating interpretation. A structural equation model further confirmed the structure of our proposed components of fighting ability, but allowing residual correlations between latent variables produces a better model fit. These analyses highlight the importance of considering fighting ability across related measures instead of using a single measure of fighting experience, fighting success, or size. Because fighting ability measures (e.g., win percentage and number of fights) reflect weight division-specific measures, results from analyses that do not incorporate the influence of fighter’s weight (Table 1) may be less valid than others (Table 4).

Although not the focus of the present paper, other sexually dimorphic acoustic parameters were associated with fighting ability. In correlation analyses, lower fo-SD and Pf predicted a greater number of UFC fight matches, and lower Pf predicted higher Elo ratings (Table 1). In addition, Pf predicted overall measures of fighting ability in the multivariate regression model (Fig. 2) and independently predicted Fighting Experience and Size (Fig. S2). Our findings extend those from previous studies showing that Pf predicts objective measures of threat potential, such as size32, strength, and physical aggression10, as well as perceived fighting ability14,62, and suggest that Pf communicates size-independent information about vocalizers’ physical formidability.

A potential statistical issue concerns the use of uncorrected p-values associated with multiple tests. However, the adjustment of p-values, such as Bonferroni correction, not only decreases the rates of Type I error, but also increases the rates of Type II error and has been highly criticized63. Additional analyses used in this study, such as multi-level modeling64, multi-variate regression, and structural equation modeling, that consider dependent variables simultaneously should reduce concerns associated with multiple comparisons.

In general, our findings are consistent with the broader perspective that men’s anatomy, behavior, and psychology have been shaped by an evolutionary history of contest competition27,65, the use of force or threat of force to exclude same-sex competitors from mates59. Contest competition should favor psychological mechanisms to attend to and assess the formidability and threat potential of competitors19. People can accurately assess physical strength from body19 and face66 images. For example, sexually dimorphic facial cues predict fighting ability among MMA fighters33,67 but see68, and using these cues participants can predict fighting outcomes above chance69. The voice appears to be another aspect of the phenotype that indicates formidability10,13,19; we showed that fo was associated with both body size and fighting experience (independent of body size) among male MMA fighters. Although associations between measures of fighting ability and fo and other sexually dimorphic acoustic parameters were small, they comport with the notion that fo is but one of many components of a vocal acoustic signal, and that voices represent one of many signals of men’s formidability17. A deep, resonant voice clearly indicates status as a physically mature or maturing male. Our findings support the further possibility that attention to differences in voice pitch among men may be functional as well, as fo and other sexually dimorphic components of men’s voices appear to provide information about differences in men’s threat potential.