Scientists find why humans evolved to have curly hair

Brazilian model Gloria Maria Fonseca Siqueira smiles during an interview. AFP

Brazilian model Gloria Maria Fonseca Siqueira smiles during an interview. AFP

Published Aug 4, 2023


Researchers from Loughborough University and Penn State University have uncovered fascinating insights into how human hair textures played a crucial role in regulating body temperature for early humans.

Their findings suggest that tightly curled scalp hair served as an evolutionary adaptation, enabling early humans to stay cool in the scorching equatorial African sun while conserving water.

The study sheds light on how this unique hair texture contributed to the growth of modern human brains.

As the sun beats down relentlessly in equatorial Africa, the scalp and top of the head receive constant and intense solar radiation as heat. To understand the impact of these conditions on human hair evolution, the research team employed a thermal manikin, a human-shaped model that simulates body heat, and human hair wigs.

The manikin was placed in a climate-controlled wind tunnel with lamps to mimic solar radiation.

The team then analysed heat gain from solar radiation under various scalp hair conditions, including none, straight, moderately curled, and tightly curled.

The results were striking. While all hair types reduced solar radiation to the scalp, tightly curled hair offered the best protection against the sun’s radiative heat. This adaptation minimised the need to sweat excessively to stay cool, thus conserving valuable water resources.

Walking upright, a defining characteristic of early humans, exposed the tops of their heads to more solar radiation.

As the human brain grew in size, it generated more heat, making efficient cooling mechanisms vital.

Sweating emerged as a way to dissipate heat, but it incurred a cost in terms of water and electrolyte loss.

Tightly curled scalp hair likely evolved as a passive mechanism to reduce heat gain from solar radiation, helping humans stay cool without overtaxing their sweat glands.

This breakthrough research offers valuable insights into the evolutionary history of human hair and brain growth. Scalp hair, as an efficient cooling mechanism, played a pivotal role in facilitating the growth of modern-day brain sizes, which distinguishes us from our early Homo erectus ancestors.

The findings, reported in the Proceedings of the National Academy of Sciences, provide crucial preliminary results that improve our understanding of human hair evolution without subjecting humans to potentially dangerous conditions.

Beyond its implications for anthropology, the study highlights the use of thermal manikins as a versatile tool for quantifying human data, which can be challenging to capture otherwise.

The multidisciplinary nature of the research allows for a comprehensive exploration of early human adaptations, uncovering a remarkable aspect of our evolutionary journey.