Zeroing in on Sexual Attraction
 The environmental contribution to homosexuality appears to be mostly prenatal, especially in men (see p 201 of the text). An example is the well documented association of male homosexuality with the number of older brothers, which holds up even when the brothers are reared apart but is not seen when the individuals are adopted. An immune reaction in the mother has been suspected, but the mechanism has defied identification; now Canadian psychologist Anthony Bogaert and his colleagues have found evidence that the immune reaction is to NLGN4Y, a protein linked to the Y chromosome, which women do not have. They found larger numbers of antibodies to the protein in women than in men; levels were highest in mothers of gay sons with older brothers, lower in mothers of gay sons with no older brothers, less in women with straight sons, and least in women with no sons. The protein is presumed to play a role in the development of synaptic functioning in the male brain; the authors suggest that the antibodies accumulate in the mother with successive male births and interfere with the masculinization of sexually differentiated brain structures. The study was small, so the findings are preliminary. Proceedings of the National Academy of Sciences, Vol 115, 302-306.
     Meanwhile, researchers still struggle to pin down which genes account for the heritablity of sexual orientation. A genome-wide study of 1,077 homosexual men and 1,231 heterosexual men has identified DNA regions on three chromosomes that appear to be linked with homosexuality. The area on chromosome 8 has been reported previously, so this finding adds support; one on chromosome 13 contains the gene SLITRK6, which is active in the hypothalamus of male mice days before birth, a time believed important in sexual differentiation of that part of the brain; and one on chromosome 14 contains the gene TSHR, which helps control thyroid function, which is atypical in male homosexuals. Scientific Reports, Vol 7, #16950 (online).
    More recently, researchers at the annual meeting of the American Society of Human Genetics have reported the results of the largest study so far of the genetics of sexual orientation. Using data from the UK Biobank study and 23andMe, which included 450,939 people with exclusively heterosexual experience and 26,890 people reporting at least one homosexual experience, they identified four DNA regions on chromosomes 11, 12, and 15 that appear to be linked with nonheterosexual behavior. A stretch of DNA on chromosome 15, previously associated with male-pattern baldness, and another on chromosome 11 were specific to men who reported same-sex experience. The chromosome 11 cluster contains a number of genes involved with olfactory receptors; olfaction is considered to play a significant role in sexual attraction. The variants could not be tied to actual genes and, in fact, the researchers are not sure whether they are within coding or noncoding stretches of DNA. The analysis did not support the results of Dean Hamer's 1993 study which suggested that region Xq28 on chromosome X is associated with same-sex behavior in males (text pp 200-201). Reported online by Science, Oct 20, 2018.

Updating Transsexual Brain Differences
Studying the brains of LGBTQ individuals helps us answer the broader question of what drives sexual preference and gender identity in all of us. Several studies of transsexual individuals suggest that some brain structures may be more similar to those of the identified sex than of the chromosomal sex, but often those studies lack agreement or have not been repeated (see text, p 194). Recent studies have not focused on individual structures as Zhou et al. did, but on white matter pathways and grey matter volume. Useful reviews can be found in The Scientist, Mar 1, 2018, in PLoS One, 8, DOI: 10.1371/journal.pone.0083947, and in Scientific Reports, 8, Article #736 (2018).

Canadian Baby Issued Health Card Without Sex Designation
The Gender Free I.D. Coalition, whose vision is "to remove all gender/sex designations from identity documents," has reported that Searyl Doty, who was born "outside the medical system" without undergoing a genital inspection, has been issued a Canadian health identification card minus the usual male/female specification. Searyl's parent, Kori Doty, who identifies herself as "non-binary trans," says that "It is up to Searyl to decide how they identify, when they are old enough to develop their own gender identity." The case, including the Canadian government's concession, illustrates the growing acceptance of the idea that a binary classification of sex and gender is both socially inadequate and scientifically unjustified. CNN Health, July 5, 2017 (online).

The Pheromone Controversy Continues
Scientists continue to argue about whether humans produce and respond to pheromones; a recent study in which the presumed male pheromone AND (androstadienone) and the presumed female pheromone EST (estratetraenol) failed to increase attractiveness ratings of photos of members of the opposite sex led Science News to question other pheromone researchers about the issue. Researcher Wen Zhou criticizes the study's design as inadequately rigorous and Martha McClintock argues that her research indicates small amounts of AND influence brain functions. The recent study's lead author believes human pheromones likely exist, but that AND and EST continue to be seen as candidates only because of journals' bias against publishing negative results. Pheromone researcher Tristram Wyatt applauds the recent push to publish negative findings, which he hopes will lead researchers to change how they look for pheromonal effects. The beauty of science is that it is self correcting; the opportunity to look at both positive and negative findings side by side will eventually lead to the correct answers. Science News, Mar 7, 2017 (online).

Females Are Dominant In A Handful of Mammal Species
One of the most reliable differences between males and females across the animal kingdom is male dominance; among 76 non-human mammalian species that exhibit leadership, for example, females are dominant among African lions, spotted hyenas, African elephants, orcas (killer whales), lemurs, and bonobos. The females, who are bonded to each other, direct food collection, decide where their group moves, hold important local knowledge, and direct fighting with other groups. In these species females have the strength advantage or they are long-lived or spend most of their life in one area. The study will be published in The Leadership Quartely; a description appears here.

How Different Are Male and Female Brains?
Gina Rippon, a cognitive neuroscientist at the University of Aston in Birmingham, UK, describes research that has dispelled several previously held beliefs about male-female brain differences. She also argues that the brain is very plastic, shaped functionally, and often physically, by experience. One example is that spatial ability is more related to whether the person plays computer games than to the person's sex. New Scientist, Feb 28, 2019.
   Unfortunately, she does not deal with well-established differences, such as differential rates of depression and autism in males and females, which beg explanation at the brain level. Research has produced variable and contradictory results, so an international team has done a meta-analsis of MRI studies of M-F differences in brain volume and density. They found reliable differences in several areas, most notably in the insula, limbic structures, basal ganglia, thalamus, and cerebellum. Further investigation will be required to determine which of these differences impact behavior and how. Neuroscience & Biobehavioral Reviews, 39, 34-50.