The Science of Hair Whorls and Laterality Part 1, The Nature Side of Nature/Nurture

Many of you have heard of hair whorls or cowlicks before and may have formed opinions that either agree with or discount the validity of claims. In the past, people like Linda Tellington-Jones put forth untested theories about a link to personality. More recently, Noche Miller expounds on the same theme in her popular Facebook page titled “Equine Swirls/Whorls Study” with 24K followers and a book titled “Understanding Horse Whorls.” The claims from both authors suggest that hair whorl traits can predict personality. However, these claims ignore that personality has nature and nurture components, so this connection is unlikely.

Hair whorls form on the scalp while the brain forms in the developing fetus at weeks 12 to 16. Hair, skin, teeth, and the brain are all parts of the fetal cell layer called the ectoderm. As the brain begins to form and grow, hair follicles form simultaneously on the scalp as the brain develops. During this early stage, the brain develops asymmetrically, with a tendency of the right side to be warped slightly forward relative to the left, and the left side distorts slightly backward relative to the right. The reverse of this asymmetry occurs in 10% to 15% of brains in animals and people. Dependent on this asymmetric torque, the hair whorls on the scalp reflect a stretch point on either the scalp’s right or left side.

Recently, scientists showed that hair whorl positions on the scalp are a genetic trait, fixed by birth, stable throughout the horse’s life (1), and highly heritable. I noted the heritability in the 1990s and wrote this prediction in the 2014 edition of Genetics and the Behavior of Domestic Animals. In essence, if you breed a high-hair whorl stallion to a high-whorl mare, there was about a 7 in 10 chance the offspring would also be high. Using percentages is a simplified way of defining heritability. Even so, I use it here for the layman not fluent in science jargon. Heritability estimates range in value from 0 to 1, with 1 as the most heritable. Geneticists in Japan recently reported the heritability estimate of the hair whorl trait in racehorses as 0.66, close to my 70% chance prediction(2). In another study of Konik horses (3), the estimate was 0.83. Both estimates in two different breeds are close to my prediction. I devised my assessment by recording every mare/stallion/offspring I encountered over ten years and meticulously recording it in my journals. I also predicted that heritability follows the high whorl. If you breed a high whorl to a low whorl, the offspring will have a hair whorl somewhere between the two but closer to the high side. High-hair whorls are dominant. Another prediction I made was high and super-high horses are more reactive and learn faster but are also prone to psychopathologies (abnormal behaviors). Interestingly, geneticists in Brazil (3) studying the genome regions associated with hair whorls found some of these genes also influence psychiatric diseases and neurological disorders, providing evidence for a consistent biological explanation for the association. I was right all along.

As a farrier, I had the perfect opportunity to study the phenomenon. I was shoeing 30 horses per week and visiting farms and barns along the front range of Provo, Salt Lake, and Ogden, three large cities in Utah. Along with the hair whorl positions and heritability estimates, working around and underneath horses daily provided an excellent opportunity to study their behavior in a job where you can get literally kicked out of the business. It was in my best interest to understand their behavior. The association of hair whorls kept me safe. Before starting on a horse, I could quickly estimate my risk before getting in a vulnerable position.

At first, the association between temperament and hair whorls was confusing. It was often highly predictive of behavior, but other times not so much. It wasn’t until years after making my first observations and recording my findings that I understood the paradox. Temperament, like personality, has components of nature and nurture. The foundation of temperament is nervous system reactivity, a genetic trait linked to autonomic nervous system (ANS) activity, which depends on sensory input. In layperson’s terms, the (ANS) receives information from the senses, sight, hearing senses, smell, and touch. As in all genetic traits, (ANS) varies between animals and people. Shy children often have high (ANS) activity, vigilance, and fearfulness. This variability also describes the horse with a high or super high hair whorl. For this simplified text, I use “reactive” to describe horses with a high hair whorl as reactive and horses with a low whorl as low reactive. Most horses have whorls in the mid-range, with fewer at the far ends of the spectrum.

Simple Summary:
The phenotype predicts the genotype, and the genotype predicts the phenotype. This complicated-sounding sentence made simple; high hair whorls (phenotype) predict that the horses have the genetic makeup (genotype) that predisposes them to be nervous, shy, and fearful. Horses with low whorls (phenotype) predict they have the genetic (genotype) that makes them laid back, outgoing, and fearless. Most horses are in-between these two extremes.

(1)Heritability estimates of the position and number of facial hair whorls in Thoroughbred horses. T. Yokomori, et.al (2019) BMC Research, Springer

(2)Genetic parameters for hair whorl traits in horses. (2021) Cruz, V.A.R., et al, Livestock Science V. 252

(3)Heritability of hair whorl position on the forehead in Konik horses. (2006) Gorecka, et al., J. Animal Breeding Genetics, V. 123