Sexual Orientation, Gender Identity, and Genetics
The Human Genome and Human Characteristics
The human genome is a complete set of nucleic acid sequences, organized as DNA, and includes both genes and non-coding sequences. It is specific to humans and encoded within 23 chromosome pairs (46 chromosomes). Each set is inherited from one's parents, and the combination determines genetic traits. Males are represented as and females as .
Deoxyribonucleic acid (DNA) carries the genetic instructions necessary for development, functioning, growth, and reproduction. DNA consists of four nucleobases: adenine (A), guanine (G), cytosine (C), and thymine (T). These bases pair up in a specific manner (A with T, and C with G) to form the structure of DNA.
The human genome comprises approximately 3 billion DNA base pairs. These pairs are the fundamental units of heredity, and surprisingly, >99% of these base pairs are identical across all people, reflecting the shared ancestry of humanity.
>1% of the human genome contains differences known as genetic variations or polymorphisms. These variations partly explain the individual differences in physical and psychological features observed among individuals. These variations contribute to diversity in traits such as eye color, height, and susceptibility to certain diseases.
A gene is a unit of DNA that codes for a specific protein. Genes are the functional units of heredity, and they provide the instructions for making proteins that carry out various functions in the body. Each gene has a specific location on a chromosome.
Variants of genes are called alleles. Different alleles can cause:
Differently shaped proteins, which can affect the protein's function.
Different amounts of protein, influencing the level of gene expression.
Types of genetic variation:
Large scale:
Chromosomal abnormalities: These involve significant changes in the number or structure of chromosomes, which can have profound effects on development and health.
Change in the number of chromosomes (whole), such as Down syndrome (trisomy 21), where an individual has an extra copy of chromosome 21.
Change in the arrangement of chromosomes (part), including deletions, duplications, inversions, and translocations.
Medium scale:
Copy number variations (CNVs): These are structural variations in the genome that result in abnormal dosage of genes. CNVs involve deletions or duplications of DNA segments that are typically 1 kilobase (kb) or larger.
Insertions/deletions (Indels): These involve the insertion or deletion of short sequences of DNA. Indels can range in size from a single base pair to thousands of base pairs.
Small scale:
Single base change (SNPs): These are the most common type of genetic variation, involving a change in a single nucleotide base. SNPs contribute to individual differences in traits and disease susceptibility.
Variations in the genome (such as a single nucleotide polymorphism – SNP) are found about every 1000th base pair. These variations serve as markers for genetic studies and allow researchers to map genes associated with specific traits.
These polymorphisms account for much of individual differences in human traits, influencing a wide range of characteristics, including physical appearance, behavior, and disease risk.
Genetic studies are conducted to give us an understanding of genetic influences on individual differences in any given trait or behaviour. These studies involve analyzing DNA samples from individuals and looking for associations between genetic variations and specific traits or behaviors.
Heritability
Heritability is a measure of the extent to which differences in people's genes account for differences in their traits. It quantifies the proportion of phenotypic variation in a population that is attributable to genetic variation.
Heritability estimates derived from twin studies are the sum total of all genetic variation, including ‘de novo’ mutations (i.e., genetic effects that are not necessarily inherited from parents). Twin studies compare the similarity of identical twins (who share 100% of their genes) to fraternal twins (who share about 50% of their genes) to estimate the heritability of a trait.
Heritability estimates do not apply to a single individual. They are population-level statistics that describe the extent to which genetic differences contribute to individual variation in a trait within a specific population.
If a trait is 45% heritable, it means that 45% of individual differences in that trait are accounted for by genetic differences between individuals. It does not mean that there is a 45% probability of a particular trait for a single individual. It indicates that genetic factors explain nearly half the observed variability in the trait among people.
Pretty much all human traits for which we can reliably measure individual differences are heritable (i.e., genetic differences partly explain differences between individuals). Heritability has been demonstrated for a wide range of traits, including physical characteristics, personality traits, cognitive abilities, and susceptibility to mental disorders.
Most human traits are ‘polygenic,’ meaning that many genes of small effect size probabilistically increase the likelihood of a trait developing. Polygenic traits are influenced by the combined effects of multiple genes, each contributing a small amount to the overall phenotype.
Genetics and Sexual Orientation
Twin study heritability estimate for same-sex sexual behaviour is approximately 20-40% in the West (Langstrom et al., 2010). This relatively modest heritability suggests that genetic factors play a role, but environmental factors are also important.
This means that 20-40% of individual differences in same-sex sexual behaviour are accounted for by genetic differences between individuals. It does not mean that there is a 20-40% probability for same-sex sexual behaviour in a single individual (Langstrom et al., 2010). The genetic contribution to sexual orientation is complex and multifactorial.
The rest of the variation in same-sex attraction is accounted for by individual-specific environmental factors. These can be factors that we typically think of as biological (e.g., intrauterine hormone exposure) or social (e.g., personal experiences and cultural influences). Intrautuerine hormone exposure during fetal development is a hypothesis.
Simple heritability estimates do not model gene-environment interplay (Langstrom et al., 2010). The interplay between genes and environment can be complex, with genetic predispositions influencing sensitivity to environmental factors, and environmental exposures modifying gene expression.
Genes that are found in molecular genetic studies often account for less variation than you would expect based on twin studies. This discrepancy suggests that current molecular genetic studies may not have captured all the genetic variants that contribute to sexual orientation.
This means we have not yet found all the genes. It also suggests that many genes of small effect size explain most of the genetically driven variation --> need HUGE samples to identify these. The effect of each gene is so small, so statistically significant results are acquired in huge pools of data.
Key findings from Ganna et al. (2019):
The underlying genetic architecture of same-sex sexual behaviour is highly complex. Sexual orientation is not determined by a single gene, but instead reflects the combined effects of multiple genetic variants.
There is no single ‘gay-gene.’ Refuting this claim as overly simplistic and misleading.
Many genes with individually small effects, spread across the whole genome and partly overlapping in females and males, additively contribute to individual differences in predisposition to same-sex sexual behaviour. The genetic architecture of sexual orientation appears to be highly distributed, with many common variants exerting small effects.
These genes cannot be used to predict same-sex sexual behaviour in a single individual. The predictive power of genetic variants for sexual orientation is limited, and genetic information should not be used to make predictions about an individual's sexual behavior.
Regardless, these findings suggest that predisposition to same-sex sexual behaviour is partly genetically influenced. The balance of genetic and environmental factors is complex and likely varies among individuals.
Some genes implicated in male same-sex sexual behaviour (Ganna et al., 2019):
Genes influencing sense of smell
Genes influencing sensitivity to male hormones
The findings from this recent study also suggest that we may need to revise how we think about sexual orientation and the continuum (Alfred Kinsey). The traditional view of sexual orientation as a linear continuum may not fully capture the complexity of human sexuality.
On the genetic level, there is no evidence for a single dimension from opposite-sex to same-sex preference – i.e., no evidence for the ‘Kinsey scale.’ Challenging the unidimensional framework of the Kinsey scale.
Ganna et al. (2019): “Overall, our findings suggest that the most popular measures are based on a misconception of the underlying structure of sexual orientation and may need to be rethought. In particular, using separate measures of attraction to the opposite sex and attraction to the same sex, …, would remove the assumption that these variables are perfectly inversely related and would enable more nuanced exploration of the full diversity of sexual orientation, including bisexuality and asexuality.” A more nuanced approach would be using two dimensions: attraction to the same and the opposite sex.
Genetics and Gender Identity
2018 review - moderate to strong heritability of gender identity. Reflecting the complex interaction of genetic and environmental factors.
Environmental influences are also important. Including social and cultural factors.
No convincing molecular genetic data to date. Further research is needed to identify specific genes associated with gender identity.
Poor understanding of the environmental variables. Further research is needed to understand the environmental components, which could include both social and biological factors such as family and hormonal exposure.
These do not need to be social, could also be e.g., intrauterine hormonal factors. More research is needed on this topic.
Genetic studies can challenge our assumptions about how different traits come about. They do not often seem to respect our theories and diagnostic systems. Revealing unexpected patterns of genetic influence.
We desperately need more well-powered, genetically informative longitudinal studies in diverse populations. To unravel the complex interplay of the human genome and environmental factors on gender identity.
Ethical Considerations of Genetic Research
Ethical considerations of genetic research into human sexual orientation and gender identity is important. Protecting the rights and well-being of individuals and communities affected by research.
Findings might be used by people of different political viewpoints and values. Use of research findings to promote specific social or political agendas.
Concerns:
Fear of eugenics: Historical and ongoing concerns about the misuse of genetic information to promote discriminatory practices.
Changing and selecting traits: Ethical implications of using genetic technologies to modify or select for certain traits.
Discrimination and stigma: Potential for genetic information to be used to discriminate against or stigmatize individuals or groups.
Medicalisation: Overemphasis on biological factors and the use of medical interventions to address social problems.
Impact on legal system: Challenges in applying genetic information in legal contexts, such as criminal justice and family law.
Impact on our understanding of free will: Questions about the extent to which genetic factors influence human behavior and decision-making.
Misuse of information e.g., for employment, insurance, or education: Concerns about the unauthorized or discriminatory use of genetic information in various settings.
Ignoring research in other areas, including social and environmental factors: Risks of neglecting the complex interplay of genetic, environmental, and social factors in shaping human traits and outcomes.
Is the science robust? Ensuring that genetic findings are based on sound scientific methodology and rigorous replication.
Nuffield: Concerns about the research. This could potentially involve concerns about the methodology, design, or the questions asked in the research being flawed.
Robustness of science depends on the trait that has been studied. Many findings are more robustly replicated in the field of behavioural genetics than in other fields. Ensuring the credibility and reliability of findings in behavioral genetic research.
Problem with lack of diversity in populations that have been studied and among researchers….Historical Context. Addressing inequities in research participation and representation.
Eugenics
Eugenics (“well born”) is the idea that humanity can be improved using selective breeding. Seeking to improve the genetic quality of a population through controlled reproduction.
Murky past of behavioural genetics. Association with eugenic policies and ideologies.
Eugenics movement linked to the establishment of behavioural genetics as a field. Influence of eugenic ideas on the early development of behavioural genetics.
Founders racist. Involvement of prominent figures in the eugenics movement who held racist beliefs.
UCL (University College London) apologises for its role in promoting eugenics. Acknowledging and addressing the institution's historical complicity in eugenic practices.
Links to early eugenicists such as Francis Galton a source of 'deep regret' to institution. Reflecting on the harmful legacy of eugenic ideas.
Effects of ‘active’ eugenics: Policies and practices aimed at directly influencing reproductive choices.
Early 1900’s: “Positive” eugenics – designed to increase fertility of those deemed to be fit; Negative eugenics – designed to decrease fertility of those deemed to be unfit (promoting reproduction among those considered genetically superior and discouraging reproduction among those considered genetically inferior)
1920s and 30s: Compulsory sterilisation of the ‘unfit’ in some countries (not Britain); In Nazi Germany selective breeding of ‘racially pure’, killing of children and adults in institutions (forced sterilization of individuals deemed genetically undesirable and the systematic extermination of individuals with disabilities and other marginalized groups)
1960s: Continued sterilisation on eugenic grounds in some countries (e.g., Canada and Sweden) (persisting legacy of eugenic practices in some parts of the world)
‘Passive’ eugenics: Policies and practices that indirectly influence reproductive choices.
Policies not designed to actively discourage reproduction but are in favour of maintaining a particular ‘status quo’. (perpetuation of existing social hierarchies and inequalities)
E.g., cis-women are the ones who carry a child and give birth. Reinforcing traditional gender roles and expectations.
Fundamental problem with eugenics: Failure to respect the diversity of human values and perspectives.
Fails to acknowledge the pluralism of values and is overly optimistic about our status as ‘designers.’ (imposition of a narrow set of values and beliefs about what constitutes a 'better' human)
Eugenics is often based on a limited number of people’s beliefs and attitudes about ‘better people,’ as well as limited and biased data. (subjectivity and bias in defining desirable traits and characteristics)
Selecting for one trait may reduce fitness in other areas. Unintended and potentially harmful consequences of selective breeding.
Genetics of complex traits probabilistic, not deterministic. (recognizing the complex interplay of inheritance and environmental factors in shaping human traits)
Violations of reproductive freedoms (This has occurred in the past (e.g., Sweden) e.g., Buchanan, et al., 2000; Rutherford, 2019). (compulsory sterilization and other coercive reproductive policies)
Should current behavioural genetics research be stopped because of past or current eugenics policies? (assessing the ethical implications of continuing research in light of historical abuses)
“This evidence [regarding the heritability of intelligence] doesn’t have any necessary policy implications. That is, you can take the heritability of learning ability or reading ability and come up with a right wing policy or a left wing policy, because policy depends on values, not just knowledge” - Robert Plomin, The Life Scientific, Radio 4 (highlighting the role of values in shaping policy decisions related to research on human traits)
Concerns
Determinism: People are concerned about genetic findings as they worry that this will lead to 'blaming biology'. Genetic determinism refers to a concern that people attribute all human traits to their genes.
Biological propensity can also be viewed positively. For example, a genetic propensity can be an explanation for why people excel at certain activities.
Genetic influences are probabilistic – yet the data are not always presented in a way that emphasises this point. Genetic influences are not set in stone, and people are liable to change.
On the other hand - people may also claim that because something is not entirely heritable, this means that it is really the environment that is the key. Another false dichotomy, which ignores that virtually all traits require genetic and environmental input.
Potential harmful implications – e.g., conversion therapy a particularly problematic example. Genetic findings related to same-sex attraction can cause people to claim its a defect, leading to attempts to 'correct' it with therapy.
Confusion re: meaning of time trends but causes of mean differences and individual differences may be very different. An example would be height, where the average height increased over the last 100 years, though the height of individual people is still heritable.
Changing traits: If we can identify genes that influence behaviour, people may use this information to try and preemptively modify people’s behaviour. People are concerned this could lead to attempts to modify behavior such as aggression or antisocial behaviour.
Worries about gene therapies and over medicalisation. People are worried genetic findings will cause people to attempt to use 'curative' gene therapies for diseases like depression.
Gene therapy for complex multifactorial traits not advocated by anyone who is up to date on research. Over medicalisation should be guarded against à ethics! Gene therapies are complex and expensive, and their safety is not fully understood.
Pre-natal selection: Refers to the practice of selecting embryos based on their genes, often to select certain traits.
Techniques: Prenatal diagnosis (PND), Preimplantation genetic diagnosis (PGD)
Most ethicists take the view that: Defensible for serious diseases (certainty), Not defensible for traits in the normal range e.g., intelligence, sexual orientation, gender identity (probability) - Most think genetic selection should be for curative purposes, not for the selection of traits.
Even if we manage to conduct an objective study, we cannot guarantee that the findings are presented in a neutral way. Importance of ethical oversight in research. Importance of responsible science communication. Even if the scientists behave ethically, there is a risk the media could misrepresent the results.
Ethical Oversight
What research questions are asked and why? (ensuring that research questions are aligned with societal values and priorities)
Who conducts research? Promoting diversity and inclusivity in the research workforce.
Is funding fairly distributed? Addressing disparities in research funding and resource allocation.
Does everyone who is capable, have an equal opportunity to pursue an academic career? (promoting equal access to education and training opportunities in research)
Who is the focus of research? (ensuring that research benefits all members of society, including marginalized and underrepresented groups)
And in what context? Considering the social, cultural, and historical context in which research is conducted.
Summary
Like in almost any area of research on humans, there are real ethical concerns regarding genetic research. Addressing these concerns is essential for ensuring that research is conducted in a responsible and ethical manner.
Some of these concerns are about the ‘fear of the unknown.’ (apprehension about the potential consequences of new scientific discoveries and technologies)
Some concerns are about potential misapplication of the findings:
Applying a biased interpretation of scientific findings to advance a political agenda
Misunderstanding (e.g., misinterpretation of statistics as applying to individuals rather than populations) (importance of accurate and accessible communication of scientific findings)
Ethical oversight is critical to protect individuals and in doing so, hopefully help society. Incorporating ethical considerations into all stages of the research process.
Ethical considerations should be re-evaluated as our knowledge about genetic and environmental influences increases. (ongoing process of reflection and adaptation in response to new scientific developments)
Research in genetics attracts considerable media attention. Therefore scientists need to be careful about the claims they make in interviews.
Both scientists and journalists have a duty to communicate findings in a responsible manner (avoid headlines like: “A gene for X”). (accurate and balanced reporting of scientific findings in the media)
We need diversity: Promoting diversity and inclusivity in all aspects of genetic research.
In researchers
In participants
In research questions
We need rigour and replication: Ensuring the reliability and validity of research findings.
Robust findings before policy (basing policy decisions on strong scientific evidence)
We need engagement between researchers, policy makers, media, and people with lived experience. A more communicative research process with society involved.