Why do so many men with non-red hair have red beards?

When my brother let his mustache grow in a bout of compassion for prostate cancer victims, I discovered a new phenomenon. All my life he'd had dark hair—but his mustache was a deep scarlet red. I started doubting our kinship. How could this be? Were we actually related? And what's up with all those men sporting red beards without having ginger hair? I decided to investigate.

To get to the bottom of this ginger mystery, I contacted the Erfocentrum, the Dutch national information centre for genetics and hereditary traits.

Genetically speaking, hair color is pretty complex. "The genes that determine hair color are so-called 'incomplete dominant hereditary traits.' This means that there isn't one single gene that's dominant over the rest, but all genes influence each other," Petra Haak-Bloem, specialist at the centre, tells me.

The same genes can express themselves differently for anyone. That allows for lots of possibilities, one of which is that the color of your head hair differs from the color of your armpit hair, pubes, or beard.

"Generally speaking, people inherit hair color not only from their parents, but also from their grandparents and earlier ancestors. So it's entirely possible that one distant ancestor had a hair color that suddenly appears again though a certain combination of genes—and that can be quite unexpected for parents," Haak-Bloem continued.

No big surprise there: your genes define your hair color. But why do so many men have deviating red beards?

The shade of hair color is determined by the amount of melanin, or pigment, in the hair. Your DNA not only encodes what kind of pigment you have, but also how much of it. "For white people the shades are dependent on two sorts of melanin: eumelanine (black pigment) and pheomelanine (red pigment). Hair cells of dark haired people only contain eumelanine. Blondes have less eumelanine. And redheads' hair contains mostly pheomelanine," Haak-Bloem says.

"More than a decade ago, researchers discovered that one gene (MC1R) on chromosome 16 plays an important part in giving people red hair. MC1R's task is making a protein called melanocortin 1. That proteine plays an important part in converting pheolmelanine into eumelanine," Haak-Bloem tells me. "When someone inherits two mutated versions of the MC1R-gene (one from each parent), less pheomelanine is converted into eumelanine. The feomelanine accumulates in the pigment cells and the person ends up with red hair and fair skin."

The unexpectedly red beard is the effect of the same mutation in the MC1R gene. When you only have one mutated MC1R, red hair can appear in (unwanted) places. But even Haak-Bloem wasn't completely sure of the mechanism. Having a deviant red beard has never been linked to any deadly diseases, so it's pretty low on the research priorities list.

In any case, it's quite possible to have a sibling with red facial hair, without one of my parents having an extramarital secret. And for all those who suffer from this non-rare, non-life threatening condition: you can't change your genes. That leaves only one option for all you half-reds: wear your ginger beard with pride.