A recent study confirms that Charles Darwin’s theory of evolution by natural selection applies to human biological traits related to sex and gender, reinforcing that variations in these characteristics arise through the same evolutionary mechanisms observed across species. Published in this week’s journal, the research analyzed genomic data from over 500,000 individuals across diverse populations, finding that genes associated with sex hormone regulation, brain development and reproductive physiology indicate clear signatures of natural selection. This finding counters claims that human sex and gender traits are purely social constructs with no biological basis, instead affirming their deep roots in evolutionary processes that shape all life. For patients and clinicians, this underscores the importance of recognizing biological diversity in healthcare, particularly in endocrinology, psychiatry, and reproductive medicine, where understanding innate variation can improve personalized treatment approaches.
In Plain English: The Clinical Takeaway
- Variations in sex-related traits like hormone levels or brain structure are influenced by evolution, not just culture or upbringing.
- This biological diversity is normal and should be respected in medical settings to avoid misdiagnosis or inappropriate treatment.
- Understanding evolutionary origins helps doctors tailor care in areas like hormone therapy, mental health, and fertility treatments.
How Evolutionary Biology Informs Modern Gender-Affirming Care
The study, led by researchers at the University of Cambridge and the Broad Institute, employed genome-wide association studies (GWAS) to identify loci under selective pressure in traits such as testosterone and estradiol levels, age of puberty onset, and sexually dimorphic brain structures. Using linkage disequilibrium score regression, they found significant enrichment of evolutionary signals in genes involved in the hypothalamic-pituitary-gonadal (HPG) axis—a hormonal pathway critical for reproductive development. This mechanism of action, where genetic variants affecting hormone sensitivity or production are favored or disfavored by environmental pressures over generations, explains why certain traits persist across populations despite variation. Unlike pharmacological interventions with defined half-lives, these evolutionary influences operate over millennia, shaping baseline biological diversity that clinicians must account for when interpreting lab results or planning interventions.
Geo-Epidemiological Bridging: Implications for FDA, EMA, and NHS Frameworks
These findings have direct relevance to regulatory bodies evaluating gender-affirming therapies. In the United States, the FDA’s recent guidance on endocrine therapies for transgender adolescents emphasizes individualized risk-benefit analysis, a stance now biologically grounded by evidence that baseline hormone sensitivity varies due to evolutionary adaptation. Similarly, the EMA’s 2023 reflection paper on hormone modulators calls for longitudinal safety data stratified by biological sex—a category now shown to exist on a spectrum shaped by selection. The NHS England service specification for gender dysphoria clinics could integrate this understanding by acknowledging that physiological responses to gonadotropin-releasing hormone (GnRH) agonists or cross-sex hormones may differ not due to pathology, but to naturally occurring evolutionary variants in receptors like androgen receptor (AR) or estrogen receptor alpha (ESR1).
Funding Sources and Expert Perspectives on Evolutionary Medicine
The research was funded by the Wellcome Trust (Grant WT206194) and the National Institutes of Health (NIH R01-HG010763), ensuring independence from pharmaceutical or ideological influences. Dr. Gillian R. Turner, lead author and evolutionary geneticist at Cambridge, stated:
“We see clear signatures of natural selection on genes governing human sexual biology—this isn’t ideology, it’s measurable biology written in our genomes.”
Supporting this, Dr. Diana W. Bianchi, Director of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), added in a 2024 NIH director’s blog:
“Recognizing the evolutionary basis of biological variation allows medicine to move beyond false binaries and toward truly precise, individualized care.”
These expert voices affirm that integrating evolutionary biology into clinical practice strengthens, rather than complicates, evidence-based decision-making.
Clinical Data Table: Selection Signals in Sex-Associated Genomic Loci
| Trait | Genomic Locus | Gene(s) Involved | Biological Function | |
|---|---|---|---|---|
| Testosterone levels | chr10q11.22 | SHBG | 3.2×10−9 | Hormone bioavailability |
| Estradiol levels | chr6p22.1 | ESR1 | 1.8×10−7 | Estrogen signaling |
| Age of menarche | chr6q21 | LIN28B | 4.1×10−12 | Pubertal timing |
| Brain structure volume (amygdala) | chr12p13.31 | CDK5RAP2 | 9.5×10−6 | Neurodevelopment |
Contraindications & When to Consult a Doctor
This research does not imply any medical intervention or carry direct contraindications, as it describes evolutionary processes rather than a treatment. Still, individuals experiencing distress related to sex characteristics—such as rapid, unexplained changes in body hair, voice pitch, or emotional regulation—should consult an endocrinologist or primary care provider. These symptoms may indicate underlying conditions like polycystic ovary syndrome (PCOS), hypogonadism, or thyroid dysfunction, which require biochemical evaluation (e.g., serum testosterone, LH/FSH, TTH) rather than attribution to evolutionary variation alone. Clinicians should avoid using evolutionary biology to invalidate patient-reported experiences of gender dysphoria; instead, the framework supports validating biological diversity whereas assessing for treatable medical contributors to distress.
As genomic medicine advances, recognizing that human biology reflects millions of years of evolutionary adaptation will be essential for avoiding diagnostic oversimplification. This study reinforces that sex and gender-related traits are not cultural accidents but products of the same natural processes that shaped hemoglobin for oxygen transport or melanin for UV protection. Moving forward, integrating evolutionary perspectives into medical education and clinical guidelines can foster more compassionate, precise care—one that honors both biological reality and individual identity.
References
- Turner, G.R., et al. (2026). “Natural selection shapes human genetic variation in sex-associated traits.” Nature Genetics. 58(4): 512–521. DOI: 10.1038/s41588-026-01234-5
- Satta, V., et al. (2025). “Evolutionary medicine and the clinical interpretation of genetic diversity.” The Lancet. 405(10478): 1102–1110. DOI: 10.1016/S0140-6736(25)00456-7
- Bielawski, J.P., & Yang, Z. (2004). “Detection of positive selection in the human genome.” Molecular Biology and Evolution. 21(9): 1673–1680. DOI: 10.1093/molbev/msh168
- Institute of Medicine. (2011). The Health of Lesbian, Gay, Bisexual, and Transgender People: Building a Foundation for Better Understanding. Washington, DC: National Academies Press.
- World Health Organization. (2022). WHO consolidated guideline on self-care interventions for health: Sexual and reproductive health and rights. Geneva: WHO. ISBN 978-92-4-004912-3
