Curly hair appears across nearly every human population, but the tightest, most coiled textures are most common among people of sub-Saharan African descent and among certain Melanesian and Aboriginal groups in the Pacific. East Asian populations tend to have the straightest hair, and European populations fall across a wide spectrum from straight to tightly curled. Those broad strokes are real, but the picture is far messier than a simple chart of “race equals hair type” would suggest. The genetics are different in each region, the evolutionary pressures are fascinating, and classification systems are finally catching up to how much overlap actually exists between groups.
General Patterns Across Populations
If you lined up a random sample of people from every continent, some trends would be obvious. People of African ancestry tend to have hair that grows in tight coils or spirals, sometimes called Afro-textured or kinky hair. East Asian populations, including Han Chinese, Japanese, Korean, Mongolian, and Tibetan groups, tend to have thick, round, straight hair. European-descended populations are the wild card: you find everything from pin-straight Scandinavian hair to tightly curled Southern European or Ashkenazi Jewish hair, with wavy textures somewhere in between.
Outside those three broad groupings, things get more interesting. Indigenous peoples of Melanesia, including parts of Papua New Guinea, the Solomon Islands, and Fiji, often have tightly curled or frizzy hair that looks similar to Afro-textured hair but arose through an entirely separate genetic pathway. The same was documented historically for Tasmanian Aboriginal people and the Negritos of the Malay Peninsula and parts of the Pacific islands.1Earth and Environmental Science Transactions of The Royal Society of Edinburgh. The Aborigines of Tasmania. Part III. The Hair of the Head compared with that of other Ulotrichi and with Australians and Polynesians South Asian populations show wide variation too, ranging from straight to deeply wavy to curly. Latin American populations, shaped by centuries of admixture between Indigenous American, European, and African ancestry, display nearly the full range of human hair textures within a single community.
A large multinational study sampling over 19,000 people across nine countries found that thick hair was most common in African populations (about 41%) and least common in Asian populations (about 26%), but these numbers speak to fiber diameter, not curl.2PubMed Central. Types and Characteristics of Hair Across the Globe: Results of a Multinational Study on 19,461 Individuals The point is worth emphasizing: curl and thickness are separate traits. You can have thick straight hair or thin curly hair. Populations differ on multiple hair properties at once, and those properties don’t always move together.
Why “Race” Is a Poor Predictor of Hair Curl
The old-fashioned classification of hair into three types, “Caucasian, Mongolian, and African,” was simple but misleading. When researchers actually measure hair curvature with instruments rather than sorting by self-reported race, they consistently find enormous overlap between groups. A geometric classification study confirmed what hairstylists already know: Asian hair is usually straight, European hair ranges from straight to curly, and African hair tends toward the curliest end. But every racial group spanned at least two or three of the measurable curl categories, making race an unreliable stand-in for curl type.3PLOS ONE. Geometric classification of scalp hair for valid drug testing, 6 more reliable than 8 hair curl groups
That overlap matters for reasons beyond academic correctness. In forensic science, drug testing, dermatology, and cosmetic product development, assuming someone’s hair type from their ethnicity leads to real errors. Two people who identify as “white” might have strikingly different hair mechanics. Two people from different continents might have near-identical curl patterns. Hair is a continuous trait, not a categorical one, and the bins we impose on it often say more about social categories than biology.
Different Genes for Straight Hair in Different Populations
One of the most striking findings in hair genetics is that straight hair evolved independently in Europe and East Asia through completely different genes. In East Asian populations, a well-studied variant called EDAR V370A is strongly associated with straight, thick hair. A study of over 1,700 individuals from Han, Tibetan, Mongolian, and Li populations found a significant additive effect, where each copy of the 370A version roughly doubled the odds of having straight hair.4PubMed. The adaptive variant EDARV370A is associated with straight hair in East Asians The EDAR gene affects the development of hair follicles, sweat glands, and teeth, and this particular variant is found at very high frequency across East and Southeast Asian populations.
In Europeans, straight hair traces to a different gene entirely: trichohyalin, or TCHH, which helps build the inner lining of the hair follicle. A genome-wide scan in three Australian cohorts of European descent found that TCHH variants explained about 6% of the variation in hair shape, and these variants reach their highest frequency in Northern Europeans.5PubMed Central. Common variants in the trichohyalin gene are associated with straight hair in Europeans That 6% might sound small, but for a single gene contributing to a complex trait, it’s a hefty chunk. The parallel is striking: two separate populations independently evolved genetic machinery for straighter hair, using totally different molecular pathways.6Human Molecular Genetics. Meta-analysis of genome-wide association studies identifies 8 novel loci involved in shape variation of human head hair
Hair shape doesn’t come down to just one or two genes, though. A large meta-analysis of European genome studies identified at least 12 regions of the genome significantly associated with hair shape, including genes involved in keratin production, growth factor signaling, and follicle structure.7PubMed Central. Meta-analysis of genome-wide association studies identifies 8 novel loci involved in shape variation of human head hair A separate scan in over 6,000 Latin Americans found 18 significant genetic signals for hair traits, including a novel gene called PRSS53 that influences hair shape in admixed populations.8Nature Communications. A genome-wide association scan in admixed Latin Americans identifies loci influencing facial and scalp hair features The genetics of curliness is genuinely polygenic, meaning dozens of genes each nudge the outcome a little, and different populations carry different mixes of those variants.
Southeast Asian Aborigines and a Third Pathway
The story gets more complex in Southeast Asia. Researchers studying Cambodian aboriginal populations discovered a region of the genome showing strong signs of natural selection that overlaps with the same TCHH gene involved in European hair variation, but with entirely novel variants not seen in other populations. Two specific mutations were enriched in these groups and sit right in the part of the protein that helps cross-link structural fibers inside the hair follicle.9National Science Review. The distinct morphological phenotypes of Southeast Asian aborigines are shaped by novel mechanisms for adaptation to tropical rainforests These variants barely exist in other continental populations, appearing at frequencies below 2%, while in Cambodian aborigines they run between roughly 29% and 32%.
This finding reinforces a wider pattern: hair shape has been under strong selective pressure in multiple places independently. The fact that different populations developed different genetic solutions to modify hair texture suggests that the environment was applying consistent pressure, even if the genetic response varied.
Why Tightly Curled Hair Likely Evolved
The leading theory for why tightly curled hair is so common in equatorial Africa connects to thermoregulation. Your brain generates a lot of heat and is extremely sensitive to overheating. Early humans living in open, sun-drenched African environments needed a way to keep solar radiation from cooking their scalps while still allowing sweat to evaporate and cool the skin.
A 2023 study using thermal manikins tested how different hair types affect heat gain from the sun and evaporative cooling from sweat. The results showed that all hair reduces solar heat hitting the scalp, but tightly curled hair provided the most protection. Hair that was more tightly curled created a thicker insulating boundary of air above the scalp, blocking more radiation without requiring as much sweat to balance the heat load.10PubMed Central. Human scalp hair as a thermoregulatory adaptation In a practical sense, curly hair acts like a built-in sun hat that lets sweat evaporate through it.
This fits with the observation that Afro-textured hair is considered the ancestral condition for modern humans. The continent-wide distribution of tightly curled hair across Africa, combined with evidence from heat studies in other mammals, supports the idea that short, curly hair evolved to maintain a cooler, drier air layer near the scalp, protecting the thermally sensitive brain.11Elsevier / Dermatologic Clinics. The Evolution of Skin Pigmentation and Hair Texture in People of African Ancestry As human populations migrated into cooler climates with less intense sun, that selective advantage faded, and variants for straighter hair could spread without penalty.
Convergent Evolution in Africa and Melanesia
One of the more interesting puzzles in hair biology is why Melanesian and some Aboriginal Australian populations have tightly curled hair that closely resembles Afro-textured hair, despite being genetically quite distant from African populations. Early researchers noted this and speculated that tightly curled hair evolved independently, or convergently, in both groups.11Elsevier / Dermatologic Clinics. The Evolution of Skin Pigmentation and Hair Texture in People of African Ancestry The environments share key features: intense UV radiation, high temperatures, and high humidity.
Genetic studies have largely confirmed this suspicion. The specific genes driving tight curl in African populations differ from those operating in Melanesian and Southeast Asian aboriginal groups. A genome-wide study in South Africa identified strong links between curliness and variation in trichohyalin, a copper transporter protein called CUTC, and the inner root sheath component keratin 74.12PubMed Central. The biology and genetics of curly hair These aren’t the same variants found in Melanesian populations. The similarity in appearance comes from similar environmental pressures pushing hair follicle biology toward the same outcome through different molecular routes.
What Actually Makes Hair Curl at the Fiber Level
Whatever the genetic starting point, the curl itself comes from asymmetry within the hair follicle. A curly hair fiber grows from a follicle whose shape and internal chemistry aren’t uniform all the way around. The cells on one side of the growing fiber are slightly different from those on the other side, and as the fiber hardens, that built-in asymmetry forces it into a curve. Think of it like a bimetallic strip: two materials bonded together that expand at different rates will bend. Hair does something analogous, with the proteins on the inner curve of a curl differing from those on the outer curve in their cross-linking and structural arrangement.
A common assumption is that the cross-sectional shape of the hair fiber determines curl, with round fibers growing straight and flat, oval fibers curling. That’s partly true but oversimplified. Research on mature hair shafts has shown that an oval cross-section acts as a synergistic factor in curl formation but isn’t the determining one on its own.13PubMed. Why is hair curly?-Deductions from the structure and the biomechanics of the mature hair shaft Plenty of people have somewhat oval hair fibers and straight hair, or nearly round fibers with noticeable wave. The internal distribution of different types of cortical cells and the pattern of disulfide bonds within the fiber matter more than shape alone.
Rare Genetic Conditions That Alter Curl
Beyond the common genetic variants that shift hair texture across populations, a handful of rare mutations can dramatically change curl pattern within a family. Conditions sometimes labeled “woolly hair” or autosomal recessive hypotrichosis produce extremely tight, fragile curls in individuals who would otherwise be expected to have straight or wavy hair based on their ethnic background. Mutations in the LPAR6 and LIPH genes have been identified in consanguineous families, particularly documented in Pakistani families, as causes of this type of hair.14PubMed. Mutations in the LPAR6 and LIPH genes underlie autosomal recessive hypotrichosis/woolly hair in 17 consanguineous families from Pakistan Separately, a mutation in the keratin K71 gene has been linked to a dominant form of woolly hair, meaning only one copy of the variant is needed for the trait to appear.15Journal of Investigative Dermatology. A Missense Mutation within the Helix Initiation Motif of the Keratin K71 Gene Underlies Autosomal Dominant Woolly Hair/Hypotrichosis
These conditions are uncommon, but they’re instructive. They show that a single gene change can override the population-level tendency for a particular hair type. They also remind us that hair curl isn’t just a cosmetic feature; the same genes and pathways are involved in follicle health, hair strength, and sometimes cardiac function. Some woolly hair syndromes are associated with heart rhythm abnormalities, which is why dermatologists occasionally flag unusual hair texture as worth a closer medical look.
How Classification Systems Are Changing
For most of the twentieth century, hair science categorized fibers into three buckets matching continental ancestry. That framework was always blunt, but it became increasingly untenable as researchers measured hair properties precisely and found that the overlap between groups dwarfed the differences. More recently, classification schemes have tried to capture the actual geometry of hair rather than sorting it by the person it came from.
The most widely used consumer system was developed by hairstylist Andre Walker, which assigns hair to types numbered 1 through 4 (straight, wavy, curly, coily) with subcategories. It’s the system you see on product labels and natural-hair forums. Researchers have pointed out that while this system is popular, it relies on qualitative visual assessment, making it vague for scientific purposes.16PubMed. Reimagining Hair Science: A New Approach to Classify Curly Hair Phenotypes via New Quantitative Geometric and Structural Mechanical Parameters L’Oréal developed a taxonomy based on measured curvature across four categories (straight, wavy, curly, kinky), but this too fails to capture the diversity within curly and coily hair types.
Newer methods use high-throughput imaging to measure the actual curvature of individual fibers in degrees per millimeter. One study developing these techniques found that when continuous curvature data was binned using the older L’Oréal thresholds, the resulting categories represented variation unevenly, with too much diversity crammed into the curliest bins and too little in the straight ones.17Scientific Reports. High-throughput phenotyping methods for quantifying hair fiber morphology The field is slowly moving toward treating hair shape as a continuous measurement rather than a categorical label tied to ancestry.
How Environment and Damage Interact with Curl
Your genes set your hair’s baseline curl pattern, but what happens to your hair after it leaves the follicle depends heavily on environment and care practices. UV radiation, humidity, heat styling, and chemical treatments all alter the hair fiber’s structure over time. Grooming habits, chemical relaxers, perming solutions, and even climate can cause color loss, brittleness, and changes in texture.18Exogenous Dermatology. Exogenous Factors in Hair Disorders None of these change the curl that will grow out of your follicle, but they change what the existing fiber looks and feels like, sometimes dramatically.
Humidity deserves special mention because curly-haired people experience it so viscerally. High humidity doesn’t just make hair frizz through water absorption. When UV exposure and high moisture combine, the chemistry inside the hair fiber becomes more destructive: water facilitates the formation of reactive oxygen species that break the disulfide bonds holding the hair’s shape together. Hair exposed to UV in humid conditions loses more protein and sustains more structural damage than hair exposed to the same UV in dry air.19Anais Brasileiros de Dermatologia. The exposome impact on hair health: etiology, pathogenesis and clinical features – Part I
This damage interacts with ethnicity-linked hair properties in ways that matter for care. African hair tends to show more surface damage from UV exposure than Asian or European hair. Asian hair, meanwhile, carries more integral lipids, which appear to offer a degree of protection against UV-induced damage.20PubMed Central. The ethnic differences of the damage of hair and integral hair lipid after ultra violet radiation Other research has found that African hair, somewhat surprisingly, carries the highest total amount of surface lipids, likely from sebaceous secretions, but that the fiber itself absorbs and loses water faster than Asian or European hair.21PubMed. The influence of hair lipids in ethnic hair properties That faster water movement helps explain why tightly coiled hair is more susceptible to dryness and breakage: moisture enters and leaves the fiber more readily, and each tight bend in the fiber is a structural weak point where breaks tend to start. Understanding this isn’t about labeling one hair type as “fragile”; it’s about recognizing that care routines genuinely need to differ based on hair properties, not just personal preference.