Testosterone Transfer Research Articles

Twin testosterone transfer hypothesis and the second-to-fourth digit ratio in females of same-sex and opposite-sex twin pairs: An exploratory study.

The twin testosterone transfer (TTT) hypothesis posits that females with male co-twins (opposite-sex, OS) might develop male-typical traits due to higher prenatal testosterone exposure. This study explored whether females of OS have lower 2D:4D digit ratios and higher testosterone levels compared to females of same-sex (SS) twin pairs. Conducted in Tamale from January to December 2022, the study included 40 participants aged 18-27 years: 10 males of OS, 10 females of OS, and 20 females of SS twin pairs. Digit ratios (2D:4D) and serum testosterone levels were measured using computer-assisted analysis and ELISA, respectively. Results showed no significant differences in 2D:4D ratios between females of OS and SS twin pairs for either the right hand (0.960 ± 0.049 vs. 0.955 ± 0.042; p = 0.766) or the left hand (0.966 ± 0.048 vs. 0.968 ± 0.047; p = 0.908). Serum testosterone levels were lower in females of OS than females of SS twin pairs (0.4 ± 0.1 vs. 0.67 ± 0.34 nmol/L; p = 0.013), but this result was not significant after multiple testing corrections (p > 0.050). The findings indicate that the TTT hypothesis may not apply, or its effects on digit ratios and testosterone levels in females of OS twin pairs are weak and not statistically significant. Further studies involving larger samples are however, recommended.

Predicting yolk testosterone allocation using ecological contexts and species-specific traits.

The prenatal transfer of testosterone (T) from mother to offspring is an important source of phenotypic plasticity. In birds, exposure to ecologically relevant stimuli, such as social competition or an attractive mate, can cause females to deposit more T into their egg yolks. Exposure to elevated yolk T can modify the expression of several fitness-related traits in offspring (e.g. growth, immune function, secondary sex traits and behaviour). Despite some of these changes being potentially adaptive, not all studies find that yolk T levels change in response to ecologically relevant stimuli. This heterogeneity is currently unexplained, limiting our ability to predict inter-generational responses to ecological change. Here, we performed a systematic literature search and found 119 observations across 39 wild species that measured inter-female variation in yolk T allocation in response to various stimuli. We used boosted regression trees, a form of machine learning, to examine whether species-specific traits or variation in study-level variables could explain variation in yolk T allocation (i.e. statistically significant vs. non-significant responses). We found that both species-specific traits and study-level variables are important predictors of significant changes in yolk T levels. Geographic range (latitude and longitude), evolutionary distinctiveness, longevity, egg mass relative to female mass, sociality, migration status and time to fledge were among the top 10 most influential predictors of the 48 examined. We also found that studies measuring or manipulating social stimuli (e.g. competition and breeding density) or breeding date were more likely to detect changes in yolk T allocation compared with studies examining other ecological contexts. Overall, these data provide several testable hypotheses concerning yolk T allocation and its adaptive value across species and contexts. Additionally, these findings can help us predict how ecological changes will affect hormonal responses in females that can shape future generations.

Intrauterine position effects in a mouse model of maternal immune activation

Rodent models of maternal immune activation (MIA) are increasingly used as experimental tools in preclinical research of immune-mediated neurodevelopmental disorders and mental illnesses. Using a viral-like MIA model that is based on prenatal poly(I:C) exposure in mice, we have recently identified the existence of subgroups of MIA-exposed offspring that show dissociable behavioral, transcriptional, brain network and inflammatory profiles even under conditions of genetic homogeneity and identical MIA. Here, we tested the hypothesis that the intrauterine positions of fetuses, which are known to shape individual variability in litter-bearing mammals through variations in fetal hormone exposure, may contribute to the variable outcomes of MIA in mice. MIA was induced by maternal administration of poly(I:C) on gestation day 12 in C57BL/6N mice. Determining intrauterine positions using delivery by Cesarean section (C-section), we found that MIA-exposed offspring developing between female fetuses only (0M-MIA offspring) displayed significant deficits in sociability and sensorimotor gating at adult age, whereas MIA-exposed offspring developing between one or two males in utero (1/2M-MIA offspring) did not show the same deficits. These intrauterine position effects similarly emerged in male and female offspring. Furthermore, while MIA elevated fetal brain levels of pro- and anti-inflammatory cytokines independently of the precise intrauterine position and sex of adjacent fetuses during the acute phase, fetal brain levels of TNF-α remained elevated in 0M-MIA but not 1/2M-MIA offspring until the post-acute phase in late gestation. As expected, 1/2M offspring generally showed higher testosterone levels in the fetal brain during late gestation as compared to 0M offspring, confirming the transfer of testosterone from male fetuses to adjacent male or female fetuses. Taken together, our findings identify a novel source of within-litter variability contributing to heterogeneous outcomes of short- and long-term effects in a mouse model of MIA. In broader context, our findings highlight that individual differences in fetal exposure to hormonal and inflammatory signals may be a perinatal factor that shapes risk and resilience to MIA.

Exploring Hematological and Biochemical Disparities in Same-Sex and Opposite-Sex Females: A Cross-Sectional Twin Study in a Ghanaian Population.

There are sex-dependent differences in hematological and biochemical variables in adulthood attributed to the predominant effects of testosterone in males and estrogen in females. The Twin Testosterone Transfer (TTT) hypothesis proposes that opposite-sex females may develop male-typical traits due to exposure to relatively higher levels of prenatal testosterone than same-sex females. Additionally, prenatal testosterone exposure has been suggested as a correlate of current circulating testosterone levels. Consequently, opposite-sex females might exhibit male-typical patterns in their hematological and biochemical variables. Despite this hypothesis, routine laboratory investigations assign the same reference range to all females. Our cross-sectional study, conducted in Tamale from January to September 2022, included 40 twins, comprising 10 opposite-sex (OS) males (25%), 10 OS females (25%), and 20 same-sex (SS) females (50%), all aged between 18 and 27 years. Fasting venous blood samples were collected and analyzed using automated hematology and biochemistry laboratory analyzers. Results indicated that levels of hemoglobin, serum creatinine, gamma-glutamyl transferase, total protein, globulins, and total testosterone were significantly higher in OS males than OS females. Conversely, total cholesterol and low-density lipoprotein cholesterol were significantly higher in OS females than OS males. Unexpectedly, levels of low-density lipoprotein cholesterol and total testosterone were significantly higher in SS females than OS females. Contrary to expectations, opposite-sex females did not exhibit male-typical patterns in their hematological and biochemical variables. This suggests that the TTT effect may not occur or may not be strong enough to markedly affect hematological and biochemical variables in OS females.

Integrating genealogy and dental variation: contributions to biological anthropology

AbstractGenealogical samples that couple dental data and documented relatedness information provide unique opportunities to examine the biological foundations of tooth variation. Over the past century, these resources have been critical for examining the various factors that influence dental phenotypes—the same traits that anthropologists regularly apply to reconstructions of past phenomena. Genealogical samples are uniquely suited to test long‐standing assumptions underlying bioanthropological practice, for example, biodistance and phylogenetic analysis, which commonly reference aspects of tooth size and form as proxies for latent genetic information. This article provides an overview of published genealogical research, with a focus on the practical implications of quantitative genetic and environmental studies of (non)human primate dentitions. To highlight the utility of genealogical samples for understanding the influence of specific non‐genetic factors on dental characters, we also present novel data on gestational hormone effects in opposite‐sex dizygotic twin pairs as a test of the twin testosterone transfer (TTT) hypothesis. This article discusses fruitful next steps in genealogical dental research, as well as important ethical considerations surrounding the use of associated datasets, which are sensitive in nature. As we forge ahead in an age of phenomics, genealogical samples are likely to play a key role in generating comprehensive genotype–phenotype maps of the dentition and in refining bioanthropological methods.

No effects of siblings and twin testosterone transfer on autistic traits.

Having twin and non-twin siblings might influence autistic traits both prenatally and postnatally. The twin testosterone transfer hypothesis suggests that girls with a twin brother are exposed to higher levels of prenatal testosterone than girls with a twin sister, and that increased testosterone exposure masculinizes neural development and increases autistic traits. Postnatally, siblings may provide example behaviour, which could reduce autistic traits. We studied pre- and postnatal influences of twin and non-twin siblings on mother and teacher-reported autistic traits in 7714 dizygotic twins. We examined the effect of sex of the proband child and of the siblings. We fitted regression models (for boys and girls separately) with sex of co-twin and having older and/or younger siblings of each sex as predictors. Girls' mother-reported autistic traits were slightly lower for those with a twin brother than those with a twin sister (β=-.08, p = .001, Cohen's d=-.13). This difference was not replicated in teacher-reported autistic traits (β = .01, p=.734). Boys' (mother and teacher-reported) autistic traits were not related to the sex of their co-twin (ps>0.50). Teacher-reported autistic traits were slightly higher if girls had an older brother (β = .07, p = .013, Cohen's d=.12). Other than this small effect, we found no effect of non-twin siblings on autistic traits in either girls or boys (ps>.18). We did not find increased autistic traits in girls with a twin brother compared to girls with a twin sister. This finding contributes to a body of literature that rejects the twin testosterone transfer hypothesis. In addition, we found little evidence for pre- and postnatal sibling influences. Our findings align with high heritability and absence of shared-environmental influences inASD.

Epigenetic consequences of hormonal interactions between opposite-sex twin fetuses.

Previous studies reported inconsistent evidence about some phenotypic traits of females in human opposite‐sex twins (opposite‐sex females [OSF]) being distinct from females in same‐sex twins (SSF). Comparatively, less evidence showed significant differences between males in OS twins (opposite‐sex males [OSM]) and males in same‐sex twins (SSM). The twin testosterone transfer hypothesis suggests that prenatal exposure of testosterone in utero may be a possible explanation for the differential traits in OSF; however, the underlying mechanism is unknown. Here, we investigated the potential epigenetic effects of hormone interactions and their correlation to the observed phenotypic traits. In the study, DNA methylomic data from 54 newborn twins and histone modification data (H3K4me3, H3K4me1, H3K27me3, and H3K27ac) from 14 newborn twins, including same‐sex females (SSF), OS twins, and same‐sex males (SSM) were generated. We found that OSF were clearly distinguishable from SSF by DNA methylome, while OSM were distinguishable from SSM by H3K4me1 and H3K4me3. To be more specific, compared to SSF, OSF showed a stronger correlation to males (OSM and SSM) in genome‐wide DNA methylation. Further, the DNA methylomic differences between OSF and SSF were linked to the process involving cognitive functions and nervous system regulation. The differential H3K4me3 between OSM and SSM was linked to immune responses. These findings provide epigenetic evidence for the twin testosterone transfer hypothesis and offer novel insights on how prenatal hormone exposure in utero may be linked to the reported differential traits of OS twins.

Corrigendum. Testing the twin testosterone transfer hypothesis-intergenerational analysis of 317 dizygotic twins born in Aberdeen, Scotland.

Study question Does having a male co-twin influence the female twin's reproductive outcomes? Summary answer Women with a male co-twin had the same chances of being pregnant and having children compared to same-sex twin pairs. What is known already According to the twin testosterone transfer (TTT) hypothesis, in an opposite-sex twin pregnancy, testosterone transfer from the male to the female co-twin occurs. A large body of literature supports the negative impact of prenatal testosterone exposure on female's reproductive health in animal models; however, evidence from human studies remains controversial. Study design, size, duration This cohort study included all dizygotic female twins in the Aberdeen Maternity and Neonatal Databank (Scotland) born before 1 January 1979. The 317 eligible women were followed up for 40 years for any pregnancies and the outcome of those pregnancies recorded in the same database. Participants/materials, setting, methods Fertility outcomes (number of pregnancies, number of livebirths and age at first pregnancy) were compared between women with a male co-twin (exposed group, n = 151) and those with a female co-twin (unexposed group, n = 166). Population averaged models were used to estimate odds ratios (OR) and 95% CI for all outcomes with adjusting for potential confounders. Main results and the role of chance There were no differences in chances of having pregnancies (adj. OR 1.33; 95% CI 0.72, 2.45) and livebirths (adj. OR 1.22; 95% CI 0.68, 2.18) between women from same-sex and opposite-sex twin pairs. Women with a male co-twin were more likely to smoke during pregnancy and, in the unadjusted model, were younger at their first pregnancy (OR 2.13; 95% CI 1.21, 3.75). After adjusting for confounding variables (year of birth and smoking status) the latter finding was no longer significant (OR 1.67; 95% CI 0.90, 3.20). Limitations, reasons for caution The dataset was relatively small. For women without a pregnancy recorded in the databank, we assumed that they had not been pregnant. Wider implications of the findings Despite the evidence from animal studies concerning the adverse effects of prenatal testosterone exposure on female health, our results do not support the TTT hypothesis. The finding that women with a male co-twin are more likely to smoke during pregnancy highlights the importance of considering post-socialisation and social effects in twin studies. Study funding/competing interest(s) European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie project PROTECTED (grant agreement No. 722634) and FREIA project (grant agreement No. 825100). No competing interests. Trial registration number N/A.

Testing the twin testosterone transfer hypothesis-intergenerational analysis of 317 dizygotic twins born in Aberdeen, Scotland.

STUDY QUESTIONDoes having a male co-twin influence the female twin’s reproductive outcomes?SUMMARY ANSWERWomen with a male co-twin had the same chances of being pregnant and having children compared to same-sex twin pairs.WHAT IS KNOWN ALREADYAccording to the twin testosterone transfer (TTT) hypothesis, in an opposite-sex twin pregnancy, testosterone transfer from the male to the female co-twin occurs. A large body of literature supports the negative impact of prenatal testosterone exposure on female’s reproductive health in animal models; however, evidence from human studies remains controversial.STUDY DESIGN, SIZE, DURATIONThis cohort study included all dizygotic female twins in the Aberdeen Maternity and Neonatal Databank (Scotland) born before 1 January 1979. The 317 eligible women were followed up for 40 years for any pregnancies and the outcome of those pregnancies recorded in the same database.PARTICIPANTS/MATERIALS, SETTING, METHODSFertility outcomes (number of pregnancies, number of livebirths and age at first pregnancy) were compared between women with a male co-twin (exposed group, n = 151) and those with a female co-twin (unexposed group, n = 166). Population averaged models were used to estimate odds ratios (OR) and 95% CI for all outcomes with adjusting for potential confounders.MAIN RESULTS AND THE ROLE OF CHANCEThere were no differences in chances of having pregnancies (adj. OR 1.33; 95% CI 0.72, 2.45) and livebirths (adj. OR 1.22; 95% CI 0.68, 2.18) between women from same-sex and opposite-sex twin pairs. Women with a male co-twin were more likely to smoke during pregnancy and, in the unadjusted model, were younger at their first pregnancy (OR 2.13; 95% CI 1.21, 3.75). After adjusting for confounding variables (year of birth and smoking status) the latter finding was no longer significant (OR 1.67; 95% CI 0.90, 3.20).LIMITATIONS, REASONS FOR CAUTIONThe dataset was relatively small. For women without a pregnancy recorded in the databank, we assumed that they had not been pregnant.WIDER IMPLICATIONS OF THE FINDINGSDespite the evidence from animal studies concerning the adverse effects of prenatal testosterone exposure on female health, our results do not support the TTT hypothesis. The finding that women with a male co-twin are more likely to smoke during pregnancy highlights the importance of considering post-socialisation and social effects in twin studies.STUDY FUNDING/COMPETING INTEREST(S)European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie project PROTECTED (grant agreement No. 722634) and FREIA project (grant agreement No. 825100). No competing interests.TRIAL REGISTRATION NUMBERN/A

Evaluating the Potential Association between Prenatal Exposure to Testosterone and Criminal Involvement and Criminogenic Traits

Criminologists have long been interested in understanding the mechanisms that create male-female differences in criminal involvement. One possible explanation that has generated a significant amount of interest is whether testosterone—including exposure to prenatal testosterone—might be central to male-female disparities in crime. We use this possibility as a springboard to examine the potential association between prenatal testosterone and multiple criminogenic outcomes. To do so, we analyze a sample of female dizygotic twin pairs drawn from the National Longitudinal Study of Adolescent to Adult Health and employ a proxy measure of prenatal testosterone based off of the twin testosterone transfer (TTT) hypothesis. The analyses revealed that prenatal testosterone is not associated with nonviolent criminal involvement, violent criminal involvement, psychopathic personality traits, being arrested, and being incarcerated. Interestingly, there was a small association with low self-control, but the effect was in the opposite direction of expectations. We conclude by discussing the implications and limitations of our study as well as considerations for future research.

Gender and STEM Subject Choice

Science, Technology, Engineering and Mathematics’ (STEM) knowledge and skills are of increasing importance to the Scottish (and UK) economy in terms of economic growth and better-paid employment opportunities. Shortages of suitably qualified individuals mean that policymakers are concerned to increase the study of STEM subjects at both tertiary and secondary education levels, as the latter feeds the former. Persistent, gendered patterns of STEM subject choice exist at all school qualification levels with, for instance, Biology more likely to be studied by females and Physics by males. These differences have been attributed to social conditioning and gender-biased environments rather than any innate, biological differences with little known about the latter. This paper used Scottish Qualifications Authority (SQA) administrative data for 2002-2009, linked to the Scottish Index of Multiple Deprivation (SIMD), to explore whether biological factors may play a part in STEM subject choice in Scottish state secondary schools. Specifically, it examined the impact that potential exposure to increased levels of testosterone, in-utero, for female twins with male co-twins (the Twin Testosterone Transfer hypothesis) may have on their STEM subject choices. Twins and a control group of closely spaced sibling pairs were identified from SQA administrative data. Logistic regression was employed to examine Maths, Biology, Chemistry, Physics, general Science and Computing subject choices. No evidence of any testosterone effect was found despite clear patterns of gender segregation. The impact of socio-economic background was stark. The odds of individuals from more disadvantaged backgrounds taking named sciences fell as deprivation levels rose. Age-14 educational choices and general age-16 attainment were seen to be critical for studying STEM subjects at Higher, the crucial qualifications for university entry, indicating that policy interventions to increase uptake need to begin well before this to redress social inclusion and gender imbalance issues.

Testosterone 2% gel (Testavan®, Testarzon®) in adult male hypogonadism: a profile of its use

Testosterone 2% (20 m/mL) transdermal gel (Testavan®, Testarzon®), is indicated to treat adult male hypogonadism, when testosterone deficiency has been confirmed by clinical features and biochemical tests. It is applied once daily using a hands-free applicator, with an initial recommended daily dosage equivalent to 23 mg testosterone, which may be increased to 46 or 69 mg/day. In clinical studies, once-daily application of Testavan 2% gel was associated with rapid and extensive absorption of testosterone, leading to normalization of testosterone levels in hypogonadal men. After application, testosterone levels achieve their peak in ≈ 2–4 h, then decrease to pre-application levels at ≈ 12 h, broadly mirroring the natural diurnal rhythm of male testosterone. Testavan 2% gel also improved sexual, physical and mental functioning, fatigue and health-related quality of life. The components of Testavan’s novel gel enhance the transdermal transfer of testosterone into the blood, allowing the application of lower doses of testosterone in smaller gel volumes relative to the application of other transdermal testosterone gels. Testavan 2% gel is applied using the applicator cap rather than by hand, reducing the potential risk of secondary transfer of testosterone.

Evidence that prenatal testosterone transfer from male twins reduces the fertility and socioeconomic success of their female co-twins

During sensitive periods in utero, gonadal steroids help organize biological sex differences in humans and other mammals. In litter-bearing species, chromosomal females passively exposed to prenatal testosterone from male littermates exhibit altered physical and behavioral traits as adults. The consequences of such effects are less well understood in humans, but recent near-doubling of twinning rates in many countries since 1980, secondary to advanced maternal age and increased reliance on in vitro fertilization, means that an increasing subset of females in many populations may be exposed to prenatal testosterone from their male co-twin. Here we use data on all births in Norway (n = 728,842, including 13,800 twins) between 1967 and 1978 to show that females exposed in utero to a male co-twin have a decreased probability of graduating from high school (15.2%), completing college (3.9%), and being married (11.7%), and have lower fertility (5.8%) and life-cycle earnings (8.6%). These relationships remain unchanged among the subsets of 583 and 239 females whose male co-twin died during the first postnatal year and first 28 days of life, respectively, supporting the interpretation that they are due primarily to prenatal exposure rather than to postnatal socialization effects of being raised with a male sibling. Our findings provide empirical evidence, using objectively measured nation-level data, that human females exposed prenatally to a male co-twin experience long-term changes in marriage, fertility, and human capital. These findings support the hypothesis of in utero testosterone transfer between twins, which is likely affecting a small but growing subset of females worldwide.

Prenatal testosterone does not explain sex differences in spatial ability

The most consistent sex differences in cognition are found for spatial ability, in which males, on average, outperform females. Utilizing a twin design, two studies have shown that females with male co-twins perform better than females with female co-twins on a mental rotation task. According to the Twin Testosterone Transfer hypothesis (TTT) this advantage is due to in-uterine transmission of testosterone from males to females. The present study tested the TTT across 14 different spatial ability measures, including mental rotation tasks, in a large sample of 19–21-year-old twins. Males performed significantly better than females on all spatial tasks, with effect sizes ranging from η2 = 0.02 to η2 = 0.16. Females with a male co-twin outperformed females with a female co-twin in two of the tasks. The effect sizes for both differences were negligible (η2 < 0.02). Contrary to the previous studies, our results gave no indication that prenatally transferred testosterone, from a male to a female twin, influences sex differences in spatial ability.

Transfer of Topical Testosterone to Subcutaneous Microdialysate, Blood and Saliva in Healthy Young Men.

We evaluated percutaneous penetration of topical testosterone and subsequent transfer to subcutaneous tissue, blood and saliva. This microdialysis trial involved eight healthy male volunteers. Five participants received a single dose of 50 mg testosterone gel on the abdominal skin and three untreated participants served as controls. Two microdialysis probes were inserted percutaneously into the abdominal subcutaneous adipose tissue. On the skin above one probe, testosterone gel was applied (ipsilateral side). A second control probe was inserted on the contralateral side. For the determination of total and free testosterone, samples of subcutaneous microdialysate, serum, and saliva were collected over six hours, frozen, and analysed using ELISA procedures. Testosterone values in the ipsilateral microdialysate of treated subjects increased significantly within 6 h after gel application compared to controls. Salivary testosterone levels showed a rapid increase within 20 min after transdermal application followed by a plateau phase with tenfold increased testosterone levels. Microdialysate testosterone of the contralateral site started to rise moderately within the normal range 1 h after administration of testosterone gel whereas total and free testosterone serum concentrations increased within 2 h in each case followed by a plateau phase. Single topical administration of testosterone gel leads to a continuous increase of testosterone in the subcutaneous ipsilateral microdialysate. Rapid salivary testosterone increase happens after gel administration followed by tenfold increased testosterone plateau values. Despite continuous influx, testosterone concentrations in serum, saliva, and contralateral microdialysate show a plateau formation thus avoiding testosterone excess.

Sex differences in non-verbal and verbal abilities in childhood and adolescence

Twin research has shown that females with male co-twins perform better than females with female co-twins on mental rotation. This beneficial effect of having a male sibling on spatial ability could be due to in-uterine transmission of testosterone from males to females (the Twin Testosterone Transfer hypothesis, TTT). The present study explored sex differences and the TTT in non-verbal and verbal abilities in a large sample of twins assessed longitudinally at 2, 3, 4, 7, 9, 10, 12, 14 and 16years of age. Females scored significantly higher than males on both verbal and non-verbal abilities at ages 2, 3 and 4. Males scored significantly higher than females on verbal ability at ages 10 and 12. The effect sizes of all differences were very small. No sex differences in non-verbal or verbal abilities were found at 7, 9, 14 and 16years of age. No support for the TTT was found at any age. The findings indicate that the twin testosterone transfer effect occurs only for specific cognitive abilities, such as mental rotation.

Egg deposition of maternal testosterone is primarily controlled by the preovulatory peak of luteinizing hormone in Japanese quail

Differential transfer of maternal testosterone (T) into egg yolk provides a means of adjusting an offspring’s phenotype to ambient environmental conditions. While the environmental and genetic driven variability in yolk T levels is widely described, the underlying mechanisms are poorly understood. Here, we investigated whether neuroendocrine mechanisms controlling ovulatory processes are associated with the regulation of yolk T deposition. Circulatory profiles of luteinizing hormone (LH), T and estradiol levels were analysed during the last 7h before ovulation in Japanese quail selected for contrasting yolk T concentrations. Moreover, the pituitary responsiveness to a single challenge with gonadotropin releasing hormone (GnRH) was evaluated. High egg T (HET) birds displayed higher concentrations of LH at 3.5h before ovulation than low egg T (LET) birds while no differences were found around the time of expected ovulation. The pre-ovulatory profile of T and estradiol levels did not differ between LET and HET females but pre-ovulatory plasma T positively correlated with LH concentrations at 6.5h and 3.5h before ovulation. The LH response to GnRH did not differ between LET and HET females. Our results demonstrate that the pre-ovulatory LH surge can determine the amount of T transferred into the egg yolk. This link between yolk T deposition and the ovulatory cycle driven variation of reproductive hormones may explain balance between the effects of circulating T on female’s reproductive physiology and yolk T on offspring phenotype.

Testosterone and Tendency to Engage in Self-Employment

Does testosterone increase the tendency to engage in self-employment? The results presented to date have been mixed. Using three different studies, we provide additional evidence on the relationship between testosterone and self-employment. Drawing on a cross section of 2,146 individuals (1,178 males and 968 females) from the National Health and Nutrition Examination Surveys’ 2011–2012 sample, and controlling for endogeneity (with red blood cell count, percentage hematocrit, and zinc supplement intake in the past 30 days as instruments), we find that serum testosterone levels are positively associated with self-employment for males (marginally significant, two-tailed test). As testosterone levels could be affected by social, economic, and biological factors during one’s life course, we draw more robust inferences by assessing whether the 2D:4D digit ratio, a marker of prenatal testosterone exposure, influences the likelihood of self-employment. From Understanding Society’s Innovation Panel Wave 6, we tested separate models for 449 males and 525 females, and our results indicate that males (respectively, females) with a lower 2D:4D ratio in their left hand, or higher prenatal testosterone exposure, have a significantly greater (respectively, marginally significant) likelihood of self-employment (two-tailed test). Finally, we examine the twin testosterone transfer effect in a sample of opposite-sex and same-sex twins from the National Survey of Midlife Development in the United States and provide additional support for the marginally significant (two-tailed test) positive association between testosterone and self-employment. Data are available at https://doi.org/10.1287/mnsc.2016.2664 . This paper was accepted by Toby Stuart, entrepreneurship and innovation.

Early-life mortality risks in opposite-sex and same-sex twins: a Danish cohort study of the twin testosterone transfer hypothesis

PurposeTo investigate the twin testosterone transfer (TTT) hypothesis by comparing early-life mortality risks of opposite-sex (OS) and same-sex (SS) twins during the first 15 years of life. MethodsWe performed a population-based cohort study to compare mortality in OS and SS twins. We included 68,629 live-born Danish twins from 1973 to 2009 identified through the Danish Twin Registry and performed piecewise stratified Cox regression and log-binomial regression. ResultsAmong 1933 deaths, we found significantly higher mortality for twin boys than for twin girls. For both sexes, OS twins had lower mortality than SS twins; the difference persisted for the first year of life for boys and for the first week of life for girls. ConclusionsAlthough the mortality risk for OS boys was in the expected direction according to the TTT hypothesis, the results for OS girls pointed in the opposite direction, providing no clear evidence for the TTT hypothesis.

Architectonics of male amygdala

The aim of this manuscript is to demonstrate that the known hormonally driven development of the male amygdalae, requires the vital use of stored memory in order that they are able to complete their recognised full structural architectonics.The hippocampus and the entorhinal cortex are strongly involved in the reception of testosterone which is the responsible hormone.The transfer of testosterone into memory and the mode of consolidation and storage of that memory are discussed.In regard to this activity, there have been suggestions concerning the possible effect of immune processes and also epigenesis and these are discussed.Finally, the controlled transfer to the male amygdala and the anabolic effect upon it are elucidated.The understanding of the hippocampal memory system is challenged by new evidence that has arisen.