Irvine, Calif., January 22, 2025 — A new paper published in the British Journal of Dermatology sheds light on one of the most distinctive and enigmatic traits of humans: long scalp hair. Conducted by researchers from the University of California, Irvine, Pennsylvania State University, and National Taiwan University, the paper delves into the evolutionary origins and significance of this uniquely human feature, as well as its implications for modern science and medicine.
Nina Jablonski, Ph.D., of Penn State and one of the paper’s authors, explains the central question the team sought to answer: “Humans grow extremely long scalp hair. 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.”
The paper proposes that long scalp hair initially evolved to protect early human ancestors in equatorial Africa from the intense heat and solar radiation of their environment. Previous research led by one of Jablonski’s doctoral students, Dr. Tina Lasisi, now of 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, which can cause dangerous dehydration. “Long, tightly curled hair was a crucial adaptation that allowed our ancestors to thrive in hot, open environments,” notes Jablonski. “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.” What the new paper did was build on the foundation of the original thermoregulatory function of long scalp hair to understand how the trait then came to have meaning in many other spheres of life.
The researchers found that long scalp hair’s role evolved over time to serve critical social functions. Early humans began to use their hair to signal health, maturity and status, further cementing its importance in human evolution. Jablonski highlights this dual significance: “Understanding when long scalp hair evolved will help to better appreciate when it acquired its essential non-biological purposes, like signaling age, health and social status in early societies.”
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. “What these examples tell us,” explains Jerry Lin, MD, Ph.D., of National Taiwan University, “is that the molecular blueprint for growing very long hair has always existed, albeit often in a ‘silenced’ state. 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,” says Maksim Plikus, Ph.D., of UC Irvine. “This knowledge could lead to treatments that help restore hair growth and alleviate the emotional distress that often accompanies hair loss.”
The paper underscores the power of evolutionary biology to answer fundamental questions about our species while opening doors to practical applications in science and medicine. By illuminating how a seemingly simple trait like long scalp hair evolved, the research not only enriches our understanding of human history but also offers hope for solving pressing challenges in dermatology and beyond.
About the University of California, Irvine Charlie Dunlop School of Biological Sciences:
Recognized for its pioneering research and academic excellence, the Charlie Dunlop School of Biological Sciences plays a crucial role in the university’s status among the nation’s top 10 public universities, as ranked by U.S. News & World Report. It offers a broad spectrum of degree programs in the biological sciences, fostering innovation and preparing students for leadership in research, education, medicine and industry. Nestled in a globally acclaimed and economically vibrant community, the school contributes to the university’s impact as Orange County’s largest employer and a significant economic contributor. Through its commitment to exploring life’s complexities, the Dunlop School embodies the UCI legacy of innovation and societal impact. For more on the Charlie Dunlop School of Biological Sciences, visit https://www.bio.uci.edu/.