It is charming that the least common hair color is also the one with the most legends around it: redheads.
One of the reasons is the rarity of this hair color, which also makes it more striking. Only 1-2% of the world’s population has red hair, making it the rarest natural hair color.
Additionally, this percentage is not evenly distributed. In Ireland, 10% of the population has natural red hair, making it the country with the most redheads.
The next would be Scotland, with 6%. Northern Europe is the region of the world with the highest number of redheads, raising the percentage globally.
The most studied gene in redheads, MC1R
One of the reasons there are so few is that the main gene responsible for red hair is recessive, the MC1R gene. If a person has only one copy of this gene, other hair colors will prevail, and they will not be redheaded. Because of this, a probability of being redheaded can be calculated.
“Wait, if it’s due to a gene, isn’t it like monogenetic diseases? Why is it a probability and not a certainty?”
Good question, myself. Let’s tackle this strand by strand.
The MC1R gene, or melanocortin 1 receptor, has various functions, but for this entry, the one that interests us is that it is a key mediator in the production of eumelanin (black and brown pigment) and pheomelanin (red and yellow pigment). Veteran readers may remember this gene from the entry on freckles.
It is a gene that also plays a role in skin pigmentation, among other things. Hence the common combination of red hair and pale skin.
In fact, it is likely that red hair color was a side effect of the evolutionary interest in having the whitest possible skin. This is why it occurs in northern Europe, with less sunlight, where ancestors wanted to absorb as much radiation as possible, and dark skin hindered this.
The gene encodes information for a receptor that, when active, causes melanocytes to produce eumelanin. When the gene is not correctly activated or is blocked, melanocytes produce pheomelanin.
But, in reality, the gene is not recessive. I lied to you before. The alleles of this gene (an allele is one of the forms or variations a gene can have) that remain constantly active are dominant. However, dysfunctional alleles are recessive. That is why you need two dysfunctional copies of the MC1R gene. The key is not the gene; it is the GENE’S ALLELE.
A single copy could do the job. These people usually have hair with brown or reddish-blonde tones.
And blondes? That’s for another entry. Let’s summarize that their eumelanin production is also quite low.
That is why, in hair heritability, people with dark colors could have light-toned offspring if they carried recessive genes for those colors and passed them on to their children.
Why that rainbow of redheads?
As you may have noticed, if it were as simple as two defective alleles equaling red hair, everyone who met that condition would have hair of the same color. It’s never simple; there are various types of redheads.
Individuals have even been found who had functional copies of the MC1R gene but were redheads.
Just like with eye color, hair color is a polygenic trait. Many genes are involved, most of which don’t even have that as their primary function. The genetics of hair color is complex.
For people with black or blonde hair, it is believed that there are at least 200 genes that, to a greater or lesser extent, affect the color.
In 2018, a study found that there were at least 8 genes controlling red hair color in a study with 350,000 redheads, the largest to date.
Several of these genes controlled hair color with “traps,” which would activate and deactivate the MC1R gene, thus influencing the color. It doesn’t matter if you have an active copy if another gene is telling it to go to sleep.
This same study found that the heritability of hair color due to the MC1R gene was 73%.
7% of redheads had at least one functional copy of the MC1R gene. More interestingly, only 15% of people with two dysfunctional copies of the gene were redheads, with the others being blonde or light brown.
Therefore, carrying less active variants of the MC1R gene is an important condition (although not essential) for being redheaded, but it is far from sufficient by itself.
Changes in hair color, whatever the shade, occur due to pigmentation and genes. Because these many genes, in turn, depend on the internal and external conditions of your body.
Is there any issue with being redheaded?
Firstly, some studies, honestly of dubious rigor, claim that redheaded people have no soul. But we are geneticists, not theologians, so that debate is not ours.
Having red hair is not an issue, but having very fair skin is. Redheads are usually more sensitive to light and ultraviolet radiation due to lower eumelanin production.
They also seem to have a lower pain threshold. The MC1R protein is, after all, a receptor with other functions. Deactivated forms cause changes in pain tolerance.
This is because the melanocytes in these people produce less proopiomelanocortin, a precursor protein of various peptide hormones, some of which participate in pain signaling.
This decreased activity has been linked by some experts to other problems, such as an increased risk of certain cancers.
On the positive side, the main objective of white skin is fulfilled in redheads. They are more efficient than most of the population in synthesizing vitamin D and are less prone to developing complications from low vitamin D levels.
Regarding hair clarity, blonde children often gain darker tones in adolescence. This happens similarly with red hair. With age, the hair follicle (the area of skin where hair grows) produces less melanin, and unpigmented hairs appear.
Curiously, redheads never have gray hair. Unlike other shades, when the pigment that gives them their color fails, the hair turns blonde or white, but not gray. That is a privilege of brunettes.
Although being able to purchase a genetic analysis from tellmeGen is a privilege accessible to everyone.
