An original theory about the origin of red hair: boglands and nitrogen!

I recently came across an original theory about the origin of red hair, which links this hair colour to boglands. You can download the paper here. 

A bog (or bogland) is a wetland that accumulates peat as a deposit of dead plant materials, often mosses, typically sphagnum moss. They are often covered in heath or heather shrubs rooted in the sphagnum moss and peat. Bogs occur where the water at the ground surface is acidic and low in nutrients. They are generally found in cooler northern climates and are formed in poorly draining lake basins. In general, the low fertility and cool climate result in relatively slow plant growth, but decay is even slower due to low oxygen levels in saturated bog soils. Hence, peat accumulates. Large areas of the landscape can be covered many meters deep in peat. Bogs are widely distributed in cold, temperate climes, mostly in boreal ecosystems in the Northern Hemisphere. The world's largest wetland is the peat bogs of the Western Siberian Lowlands in Russia, which cover more than a million square kilometres.

A bog in Lauhanvuori National Park, Isojoki, Finland

The anaerobic environment and presence of tannic acids within bogs can result in the remarkable preservation of organic material. Finds of such material have been made in Slovenia, Denmark, Germany, Ireland, Russia, and the United Kingdom. They have yielded extremely well-preserved bog bodies, with hair, organs, and skin intact, buried there thousands of years ago after apparent Germanic and Celtic human sacrifice. Excellent examples of such human specimens include the Haraldskær Woman and Tollund Man in Denmark, and Lindow man found at Lindow Common in England (here a list of the most important bog bodies). The Tollund Man was so well preserved that when the body was discovered in 1950, the discoverers thought it was a recent murder victim and researchers were even able to tell the last meal that the Tollund Man ate before he died: porridge and fish. This process happens because of the low oxygen levels of bogs in combination with the high acidity.

As you can see in the photo below, the high levels of acidity darken the skin of these bodies, which often exhibit red hair. This led to the hypothesis that the high nitrogen level in boggy environments may be the cause of the red hair colour. The interaction between nitrogen and keratin in hair can lead to a chemical reaction that results in red pigmentation, regardless of the individual’s original hair colour.

Grauballe Man

I quote from the paper:

Building on these observations, this study posits that prolonged exposure to such environments could lead to genetic adaptations over generations. The hypothesis suggests that the nitrogen-rich conditions could exert selective pressure, favoring individuals with genetic mutations that produce red hair. These mutations might confer some survival advantages in boggy environments, possibly through mechanisms related to UV protection or thermoregulation. As a result, red hair could become a heritable trait within populations living in or around these regions.

[...]

In addition to direct genetic effects, nitrogen exposure may have also influenced epigenetic mechanisms. Epigenetics involves changes in gene expression that do not alter the DNA sequence but can be heritable. Prolonged exposure to high nitrogen levels could have triggered epigenetic modifications that enhanced the survival and reproductive success of individuals in these environments. Over time, these epigenetic changes could become stabilized in the population, contributing to the genetic adaptation observed today.

However, the author concludes by saying that the exact mechanisms and pathways of this process remain to be fully elucidated.