First, work in a variety of animal models has shown that sexual partner preference can be experimentally modified by perinatal treatments with sex steroids: masculinization following exposure to testosterone or its estrogenic metabolites, and feminization in the (relative) absence of these steroids during a critical period of development. Three types of biological mechanisms have been identified in this context ( 4 – 7). In contrast, many scientists are now convinced that biological processes during embryonic and early postnatal life play a major role in the control of sexual orientation. Theories relying mainly on psychological and social mechanisms contend that the newborn is essentially neutral and that sexual orientation develops during infancy and childhood through a variety of socializing influences. Why the obverse questions probing the causes of heterosexuality attracts no attention remains enigmatic.
However, no field of research subject to this debate generates more heated controversies than those probing the proximate causes of sexual orientation, particularly its less-frequent and thus, perhaps, more-perplexing form: homosexuality. The nature–nurture debate still rages in the minds of many scientists and scholars, despite the consensus that these are complementary rather than mutually exclusive explanations. This study provides the first data-based explanation for the FBO effect and adds a significant chapter to growing evidence indicating that sexual orientation is heavily influenced by prenatal biological mechanisms rather than by unidentified factors in socialization. ( 3) present direct biochemical evidence indicating that the increased incidence of homosexuality in males with older brothers results from a progressive immunization of the mother against a male-specific cell-adhesion protein that plays a key role in cell–cell interactions, specifically in the process of synapse formation, during development called neuroligin 4 Y-linked, or NLGN4Y. Despite this compelling evidence, a mechanism to account for the effect remained elusive.
This startling phenomenon was confirmed in multiple studies based on independent populations totaling over 10,000 subjects, and a meta-analysis indicated that between 15% and 29% of gay men owe their sexual orientation to this effect ( 2). Their first investigation indicated that each older brother increased the probability of being gay by about 33% ( 1). When using a search engine such as Google, Bing or Yahoo check the safe search settings where you can exclude adult content sites from your search results Īsk your internet service provider if they offer additional filters īe responsible, know what your children are doing online.Twenty years ago, Ray Blanchard and Anthony Bogaert demonstrated that the probability of a boy growing up to be gay increases for each older brother born to the same mother, the so-called fraternal birth order (FBO) effect. Use family filters of your operating systems and/or browsers Other steps you can take to protect your children are: More information about the RTA Label and compatible services can be found here. Parental tools that are compatible with the RTA label will block access to this site. We use the "Restricted To Adults" (RTA) website label to better enable parental filtering.
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