Testosterone and estrogen are essential for male behaviors in vertebrates. How these two signaling pathways interact to control masculinization of the brain and behavior remains to be established. Circulating testosterone activates the androgen receptor (AR) and also serves as the source of estrogen in the brain. We have used a genetic strategy to delete AR specifically in the mouse nervous sys...

The hypothalamic-pituitary-gonadal (HPG) axis plays a critical role in the control of reproduction. Two key hormonal components of the HPG axis are gonadal steroids and gonadotropin-releasing hormone (GnRH). Gonadal steroids are known to organize the development of neural substrates which control adult reproductive behavior; GnRH is required for normal reproductive structure and function. The p...

Among early modern humans, a woman would face stronger competition for a mate the further away she was from the equator. Men were less available because they 1) hunted over longer distances that increased male mortality proportionately and 2) were less able to offset the resulting man shortage through polygyny. The longer the winter, the costlier it became to provision a second wife and her chi...

Bivalves of the families Mytilidae and Unionidae show a unique mode of mitochondrial DNA inheritance called doubly uniparental inheritance. In addition to receiving the maternally transmitted mtDNA lineage, males receive a separate mtDNA genome from their fathers. This system is sometimes compromised, in that female genomes are occasionally recruited into the male cycle of inheritance. These ma...

Males and females score differently on some personality traits, but the underlying etiology of these differences is not well understood. This study examined genetic, environmental, and prenatal hormonal influences on individual differences in personality masculinity-femininity (M-F). We used Big-Five personality inventory data of 9,520 Swedish twins (aged 27 to 54) to create a bipolar M-F perso...

Disorders of Sex Development (DSD) remain a fascinating challenge for the paediatricians, endocrinologists, biologists, psychiatrists, geneticists, radiologists, surgeons and for the whole society. This article aims at highlighting the current controversies and questions met with genital reconstruction in children born with abnormal genitalia. The main current techniques of masculinization and ...

While the tracheosyringeal motor neurons of anesthetized male zebra finches fire in response to acoustic stimuli, the same motor neurons in females show no such response. Females masculinized by estradiol implants on Days 1 or 2 after hatching may develop auditory responses in their tracheosyringeal motor neurons; the presence of the response is directly related to the degree of masculinization...

Sex steroids play major roles in vertebrate sexual differentiation. Unexpectedly, we now find that exposure to elevated levels of the naturally occurring stress hormone cortisol can also masculinize sexually dimorphic morphological characters and behaviour in adult female mosquitofish (Gambusia affinis) in a dose-dependent manner. Females masculinized by cortisol developed elongated anal fins w...

Previous research demonstrates that prenatal testosterone exposure increases aggression, possibly through its effects on the structure and function of neural circuits supporting threat detection and emotion regulation. Here we examined associations between regional gray matter volume, trait aggression, and the ratio of the second and fourth digit of the hand (2D:4D ratio) as a putative index of...

Previous studies have shown that male faces with extreme features associated with testosterone are perceived as dominant and masculine. Women have been reported to prefer more masculinized male faces as they may consider testosterone markers to be an 'honest' indication of good health, and such considerations may underlie their aesthetic preferences. However, pronounced testosterone facial mark...