Why some people have curly hair, unibrows or go grey has been discovered by scientists. For the first time, researchers have discovered the genes that drive our "luxuriant scalp hair", potentially paving the way for cosmetic applications and forensic reconstructions.
The team from UCL analysed over 6,000 people across Latin America looking for specific genes relating to the hair on our heads – including head hair, beards and eyebrows. Publishing their findings in the journal Nature Communications, they found genes associated with greying, shape and density (i.e. how thick the hair is).
Participants came from Brazil, Colombia, Chile, Mexico and Peru. They were made up of 45% males and 55% females and individuals had mixed European, Native American and African ancestry, meaning there was massive variation in head hair appearance.
Their findings pinpointed the genetic controls that lead to different hair types – previously researchers had only identified the genes behind colour and balding. The team's genome-wide association study identified 10 genetic variations that influence the natural features of head and facial hair.
They found the IRF4 gene was associated in greying of the hair. This gene is known to be involved in hair colour and plays a role in regulating the production and storage of melanin (which determines hair, skin and eye colour). Because grey hair is caused by a lack of melanin in the hair, understanding IRF4's role in this could lead to the development of cosmetic applications by slowing or blocking the process, thereby delaying greying of the hair.
For curly hair, they found the gene PRSS53 plays a role. Desmond Tobin, one of the study authors, explained that this enzyme is active in the part of the hair follicle that shapes the growing hair fibre.
"An enduring fascination of human evolution has been our peculiarly luxuriant scalp hair, and finding a new variation in the Protease Serine S1 family member 53 (PRSS53) gene provides an important insight into the genetic controls underpinning scalp hair shape and texture," he said. "This new genetic variation, associated with straight hair in East Asians and Native Americans, supports the view that hair shape is a recent selection in the human family."
Meanwhile, the EDAR gene was found to play a role in beard thickness and hair shape, the FOXL2 for eyebrow thickness and PAX3 for unibrow – or monobrow – prevalence. Findings also showed most of the variations of each hair traits did not overlap.
Lead author Kaustubh Adhikari said: "It has long been speculated that hair features could have been influenced by some form of selection, such as natural or sexual selection, and we found statistical evidence in the genome supporting that view. The genes we have identified are unlikely to work in isolation to cause greying or straight hair, or thick eyebrows, but have a role to play along with many other factors yet to be identified."
In terms of implications, the team wrote: "There is currently great interest in exploring whether hair appearance can be modified as it is formed in the hair follicle. This includes evaluating whether hair greying could be slowed or blocked, and elucidating the mechanism by which IRF4 influences hair greying could provide targets of intervention for this purpose. Similarly, modulating the activity of PRSS53 in the IRS and medulla is a candidate pathway with a view to purposefully altering hair shape.
"The genetics of hair appearance is also of interest in anthropology and forensics, particularly for the prediction of hair features based on genetic information," they wrote. "The implementation of this so-called 'forensic DNA phenotyping' promises to contribute an investigative tool in cases where a biological sample is available but there is lack of other information regarding the identity of its contributor."