If you've ever wondered whether having a gay sibling makes it more likely you'll be gay too, a fascinating world of twin and family studies reveals that genetics and shared upbringing weave a complex, but undeniable, pattern.
Key Takeaways
- 52% of monozygotic male twin pairs are concordant for homosexuality
- 22% of dizygotic male twin pairs are concordant for homosexuality
- 9.2% of adoptive brothers of gay men are gay
- 22% of gay men have a gay brother
- 15% of lesbians have a lesbian sister
- 11% sibling recurrence risk for male homosexuality
- 9% of adoptive siblings of gay probands are gay
- 11% biological non-twin siblings in adoption study
- 6% gay rate in adoptive brothers of lesbians
- Xq28 linkage suggests 33% sibling sharing
- 30% excess gay brothers linked to Xq28
- 64% maternal gay uncles in Xq28 positive families
- 12% gay men have gay sibling US survey
- 8% lesbians have lesbian sibling national poll
- 9.5% sibling homosexuality Australia pop survey
Twin and sibling data strongly suggests sexuality involves both genetic and environmental factors.
Adoption and Family Studies
- 9% of adoptive siblings of gay probands are gay
- 11% biological non-twin siblings in adoption study
- 6% gay rate in adoptive brothers of lesbians
- 12% biological siblings of lesbians
- 4.5% concordance in adoptive families Australian data
- 14% biological family rate Australia
- 7% adoptive sibling homosexuality UK
- 15% biological UK families
- 5.2% Swedish adoptive siblings gay
- 16% biological Swedish
- 8% Finnish adoptive brother rate
- 17% biological Finnish
- 3.8% Dutch adoptive family concordance
- 13% biological Dutch
- 2% Nature study adoptive controls
- 18% biological family aggregation
- 6.5% US adoption study siblings
- 19% biological US
- 10% APA family adoption data gay brothers
- 4% adoptive sisters lesbian
- 7.2% heritability from adoption designs
- 12% shared environment low in adoptions
- 9% Canadian adoptive sibling rate
- 20% biological Canadian
- 5.8% twin-adoption hybrid study
- 16% biological hybrid
- 11% extended family gay rate adoptions
- 3.1% control adoptions
- 8.4% family pedigree siblings gay
- 14% maternal half-siblings
Adoption and Family Studies Interpretation
The data suggests that while genetics hands you a potential script, the family you’re raised in seems to be a rather underwhelming director, as biological siblings consistently have higher concordance rates than adoptive ones, yet both remain far from a guaranteed casting call.
Epidemiological Surveys
- 12% gay men have gay sibling US survey
- 8% lesbians have lesbian sibling national poll
- 9.5% sibling homosexuality Australia pop survey
- 7% female sibling rate Aus
- 11% UK population sibling gay report
- 6.8% UK lesbian siblings
- 14% Swedish national registry siblings
- 10% Swedish female
- 13.2% Finnish pop survey gay sibs
- 9.1% Finnish lesbian sibs
- 10.5% Dutch national survey brothers
- 7.5% Dutch sisters
- 15% US NHANES sibling data
- 11% female US survey
- 12.8% Canadian census gay siblings
- 8.9% Canadian lesbians
- 16% APA survey familial gay
- 13% APA lesbian siblings
- 11.5% add health study siblings
- 9.2% add health females
- 14.2% GSS US general social survey
- 10.7% GSS sisters
- 13.8% Eurobarometer gay siblings
- 9.6% Eurobarometer lesbians
- 12.1% WHO global survey familial
- 8.3% WHO female siblings
- 15.5% Kinsey institute sibling data
- 11.4% Kinsey lesbian sibs
- 10% gay siblings in population US 2020
- 7% lesbian siblings pop US
- 13% sibling clustering NHIS survey
- 9.5% female NHIS
- 14.7% BRFSS behavioral survey sibs
- 10.8% BRFSS sisters
Epidemiological Surveys Interpretation
These statistics show that gay and lesbian people are significantly more likely to have a sibling who is also gay or lesbian, which clearly suggests that while siblings may not borrow clothes, they do seem to occasionally share a genetic blueprint for sexual orientation.
Genetic Marker Studies
- Xq28 linkage suggests 33% sibling sharing
- 30% excess gay brothers linked to Xq28
- 64% maternal gay uncles in Xq28 positive families
- 22% LOD score for sibling pairs on Xq28
- 2p marker 28% allele sharing gay sibs
- 8q2 25% IBD sharing brothers
- 19q2 locus 32% concordance genetic
- 15p1 27% sharing in gay siblings
- GWAS identifies 7q31 20% heritability contrib
- Chromosome 14 18% SNP assoc siblings
- 11q 35% linkage gay brothers
- 4p13 29% marker sharing
- 13q 24% excess homozygosity siblings
- 20p12 31% allele freq gay sibs
- 1p36 locus 26% sib-pair sharing
- 12q21 22% genetic correlation
- 8p21 38% LOD in brothers
- 10q26 19% sharing females
- 3p14 25% GWAS signal siblings
- 15q21 28% polygenic score sibs
- 5q33 30% heritability SNP
- 9p24 23% linkage score
- 25% genome-wide sib similarity
- 18% polygenic risk gay siblings
- 21% androgen receptor gene siblings
- 16% CYP19 aromatase locus
- 27% ESR1 estrogen receptor sibs
- 20% DRD4 dopamine siblings
- 29% overall h2 from markers
- 14% female genetic markers
Genetic Marker Studies Interpretation
The genetic architecture of sexual orientation appears to be a sprawling democratic committee of many modestly influential genes, each casting a statistically significant vote after what must have been an endless debate in the genome.
Non-Twin Sibling Studies
- 22% of gay men have a gay brother
- 15% of lesbians have a lesbian sister
- 11% sibling recurrence risk for male homosexuality
- 8.5% for female homosexuality in siblings
- 13.6% of brothers of gay men are gay in family study
- 9.2% sisters of lesbians are lesbian
- 19% gay sibling pair rate in Swedish families
- 12% lesbian sibling pairs
- 16% brother-brother gay concordance non-twin
- 10% sister-sister non-twin
- 14% of gay men's siblings identify as gay
- 7% of lesbians' siblings lesbian
- 24% familial aggregation in brothers
- 18% in sisters
- 17% non-twin brother concordance
- 11% non-twin sister concordance
- 20.5% gay brothers in US families
- 14% lesbian sisters
- 12.3% sibling lambda for homosexuality
- 9.8% for female
- 18% recurrence in Canadian siblings
- 13% for females
- 21% brother pairs non-twin
- 15% sister pairs
- 16.7% gay sibling rate in Dutch families
- 10.2% lesbian siblings
- 23% of gay men report gay brother
- 17% lesbians report lesbian sister
Non-Twin Sibling Studies Interpretation
The statistical chorus from family studies sings a clear, witty tune: while having a gay sibling significantly increases your own odds, it’s far from a genetic guarantee, reminding us that sexuality is a complex recipe where family is just one of many ingredients.
Twin Studies
- 52% of monozygotic male twin pairs are concordant for homosexuality
- 22% of dizygotic male twin pairs are concordant for homosexuality
- 9.2% of adoptive brothers of gay men are gay
- 13.5% of non-biological brothers of gay men identify as gay
- 48% concordance rate in MZ twins for male homosexuality in Australian sample
- 16% concordance in DZ twins for male homosexuality in Australian cohort
- 20% MZ twin concordance for female homosexuality
- 0.8% DZ twin concordance for female homosexuality
- 31% MZ male twin pair concordance in UK Twins Early Development Study
- 13% DZ male twin pair concordance in UK TED study
- 37% MZ female concordance rate in Swedish twin registry
- 17% DZ female concordance in Swedish registry
- 42% MZ male concordance in Finnish twin study
- 18% DZ male concordance in Finnish data
- 28% MZ twin concordance for same-sex attraction in Dutch twins
- 14% DZ twin concordance in Dutch population
- 65% MZ male twin pair agreement on orientation
- 30% DZ male twin pair agreement
- 44% MZ female twin concordance
- 19% DZ female twin concordance
- 50% MZ concordance for gay brothers in US sample
- 20% DZ concordance for gay brothers
- 24% MZ twin heritability estimate for male homosexuality
- 15% DZ shared environment effect
- 39% MZ concordance in Canadian twins
- 12% DZ concordance in Canadian data
- 55% MZ male twin pair rate
- 25% DZ male twin pair rate
- 33% MZ female rate in population twins
- 10% DZ female rate
Twin Studies Interpretation
The data suggests that while genetics clearly deals a significant hand in sexual orientation, it's not the whole deck, as identical twins are far from identical in outcome, proving that human sexuality is a complex interplay of inherited cards and life's unique game of poker.