Written in Our Genes
Hair texture is substantially determined by genetic inheritance. The curl pattern, fibre diameter, cross-section shape, and growth characteristics of an individual’s hair are the products of multiple genes interacting with one another and with environmental factors. This genetic basis is precisely why hair discrimination is, in a meaningful sense, discrimination against inherited characteristics — a fact with direct implications for legal protection.
Understanding the genetics of hair texture also underpins CROWN’s research programme and diagnostic technology, which must accurately characterise hair across the full range of human genetic diversity.
Key Genes and Pathways
Hair texture is a polygenic trait — influenced by many genes, each contributing a small effect. Research has identified several key genes and molecular pathways:
EDAR (Ectodysplasin A Receptor). One of the best-characterised genes affecting hair morphology. A variant (370A) found predominantly in East Asian populations is associated with thicker hair fibres, straighter hair, and increased eccrine sweat gland density. This variant is thought to have been positively selected during human evolution in East Asia.
Trichohyalin (TCHH). This gene encodes a structural protein involved in hair follicle development. Variants in TCHH are associated with differences in curl pattern, particularly in European populations. Research has linked specific TCHH variants to straight versus curly hair phenotypes.
KRT genes (Keratin gene cluster). The keratin proteins that form the structural core of hair are encoded by a family of genes. Variations in these genes affect the organisation and cross-linking of keratin filaments within the hair shaft, influencing fibre strength, elasticity, and curl maintenance.
OFCC1. Genetic studies have identified variants near the OFCC1 gene associated with hair shape in diverse populations, though the functional mechanism is still being investigated.
FGFR2 (Fibroblast Growth Factor Receptor 2). Involved in hair follicle development and cycling, variants in this gene have been associated with differences in hair morphology across populations.
PRSS53. A recently identified gene associated with hair shape variation in Latin American populations, highlighting the complexity of hair genetics in admixed populations.
Polygenic Inheritance
Because hair texture is polygenic, it does not follow simple Mendelian inheritance patterns. Two parents with similar curl patterns can produce children with different textures, and mixed-heritage families often display a wide range of hair types among siblings. This genetic complexity has several implications:
Prediction is imprecise. Genetic testing cannot reliably predict hair texture from genotype alone, because the interaction effects among multiple genes (epistasis) and between genes and environment are complex and incompletely understood.
Classification is continuous. Hair texture exists on a continuous spectrum, not in discrete categories. The Walker system’s categorisation into types 1–4 imposes artificial boundaries on what is genetically a continuous distribution.
Diversity is the norm. Within any population — and particularly within populations with diverse genetic ancestry — hair texture varies enormously. Characterising an entire ethnic group by a single hair type is genetically inaccurate.
Evolutionary Context
The diversity of human hair texture has evolutionary origins. Different hair morphologies are thought to have been shaped by natural selection in response to environmental pressures:
Thermal regulation. The tightly coiled structure of Afro-textured hair creates an insulating air layer that protects the scalp from direct UV radiation while allowing airflow for cooling — an adaptive advantage in the tropical environments of sub-Saharan Africa where modern humans evolved.
UV protection. The dark pigmentation commonly (but not exclusively) associated with tightly coiled hair provides UV protection for the scalp, reducing skin cancer risk in high-UV environments.
Climate adaptation. The straight, thick hair common in East Asian populations may have been selected for its insulating properties in cold environments, while the variable textures found in European populations may reflect adaptation to temperate climates.
These evolutionary explanations are hypotheses supported by varying levels of evidence. What is clear is that hair diversity across human populations reflects deep evolutionary history — making hair texture one of the most ancient and genetically grounded dimensions of human physical variation.
Genetics and the Legal Argument
The genetic basis of hair texture has direct relevance to legal debates about hair discrimination protection. The traditional legal distinction between “immutable” characteristics (protected) and “mutable” characteristics (not protected) has been used to deny protection for hairstyles — on the grounds that an individual can change their hairstyle.
Genetic research undermines this argument. Hair texture — the fundamental physical property of hair — is genetically determined and immutable. Protective hairstyles are not arbitrary fashion choices but practical responses to genetically determined texture. Requiring individuals to chemically or thermally alter their genetically determined hair texture to avoid discrimination is requiring them to change an inherited characteristic — precisely the type of burden that anti-discrimination law is designed to prevent.
CROWN’s CDI research includes genetic context as part of the evidence base, connecting the biological reality of hair texture to the social reality of discrimination. The CROWN Diagnostic’s objective measurement of hair characteristics provides the data link between what genes produce and what institutions penalise.
The Future of Hair Genetics Research
Understanding the genetics of hair texture is still an active area of research. Key questions include:
- Which additional genes contribute to the full range of human hair diversity?
- How do gene-gene interactions (epistasis) produce the complex textures observed in mixed-heritage individuals?
- What epigenetic factors (environmental influences on gene expression) affect hair characteristics over the lifespan?
- Can genetic knowledge improve diagnostic accuracy and personalised hair care?
As genetic research advances, CROWN’s data infrastructure — linking genetic ancestry data with detailed, sensor-verified hair characterisation — will provide a resource for answering these questions at population scale. The CROWN Hair Commons is designed not only for discrimination research but as a resource for advancing the fundamental science of human hair diversity.
