Treating hair loss may be as simple as developing therapies to flip a molecular "switch," according to a new study by researchers from Penn State, the University of California, Irvine, and National Taiwan University.
The researchers reviewed the biological and social evolution of human scalp hair. Based on their analysis, they proposed a novel theory that points to a molecular basis underlying the ability to grow long scalp hair. In short, human ancestors may have always had the ability to grow long scalp hair, but the trait remained dormant until certain environmental and biological conditions - like walking upright on two legs - turned on the molecular program. The team published their findings, which they said could serve as the basis for future experimental work, in the British Journal of Dermatology.
"Humans grow extremely long scalp hair," said Nina Jablonski, the Evan Pugh Professor Emeritus of Anthropology at Penn State and paper co-author. "Likewise, attributes of scalp hair - its length, shape, color and loss of hair - play an essential role in social communication. They signify our ancestry, age, health, sexual maturity and social status, to name but a few. And yet, despite the importance of having long scalp hair, we know very little about how this feature of human skin came about and how it is regulated."
Previous research led by one of Jablonski's doctoral students - Tina Lasisi, who graduated in 2021 and is now an assistant professor of biological anthropology at the University of Michigan - had shown that tightly curled hair, in particular, served as an effective shield against the sun, reducing the need for excessive sweating that can cause dangerous dehydration. Building on this work, the researchers proposed that long scalp hair initially evolved to protect early human ancestors in equatorial Africa from the intense heat and solar radiation of their environment, and then it came to have meaning in many other spheres of life, such as signaling age, health, maturity and social status.
"Long, tightly curled hair was a crucial adaptation that allowed our ancestors to thrive in hot, open environments," Jablonski said. "This hair type not only reduced heat exposure but also conserved vital water and electrolytes, which could mean the difference between life and death in such extreme conditions."
Understanding when long scalp hair evolved will help to better appreciate when it acquired its essential non-biological purposes, Jablonski said.
While long hair is rare among mammals, it is not entirely unique to humans. Animals like male lions, orangutans and even now-extinct woolly mammoths also grew remarkably long hair, albeit for different reasons, according to the researchers.
"What these examples tell us is that the molecular blueprint for growing very long hair has always existed, albeit often in a 'silenced' state," said co-author Sung-Jan "Jerry" Lin, chair and distinguished professor of biomedical engineering at the National Taiwan University. "When human ancestors evolved their ability to grow extremely long scalp hair, it was likely accomplished by just a few genetic tweaks that reactivated a dormant program rather than via the evolution of an entirely new molecular mechanism."
The findings have broader implications for medical research, particularly in addressing hair loss, a condition that impacts millions worldwide.
"Understanding how human scalp hair follicles normally grow very long hair will naturally result in novel molecular targets for more efficacious therapies for hair loss," said co-author Maksim Plikus, professor of developmental and cell biology at the University of California, Irvine. "This knowledge could lead to treatments that help restore hair growth and alleviate the emotional distress that often accompanies hair loss."
Lo-Yu Chang, graduate student in the Department of Molecular Biology and Genetics, School of Medicine, Johns Hopkins University, also contributed to this research. The Taiwan Bio-Development Foundation, National Taiwan University Hospital and Taiwan National Science and Technology Council supported this work.
