How is it that red hair shows up in people of African descent?
-A curious adult from California
A redhead of African descent is about as common as a Caucasian with red eyes. And there's a good reason for this -- being an albino causes them both.
Except when people are of mixed ancestry, red hair in Africans is usually caused by a kind of albinism. When people think of albinos, they tend to think of white hair, pale skin and red eyes. While this is true for Caucasians, albinism works differently in people of African descent.
There are a few different kinds of albinism in people of African descent, but the one that gives red hair is called rufous albinism. People with this condition have a red-bronze skin color, ginger-red hair, and blue or brown eyes.
How is someone an albino? All of our coloring -- our skin, hair, and eye colors -- comes from melanin. Melanin is just a pigment, or colored chemical substance, like the ones that are used to dye your clothes or maybe even your hair! Melanin comes in two different forms -- pheomelanin (the red kind) and eumelanin (the brown kind).
Being an albino just means that your body doesn't make melanin the right way. There are lots of different genes that can be mutated to cause albinism.
Why are so many genes involved? To make each kind of melanin, your cells have to carry out several chemical steps. It's kind of like an assembly line. And just like in an assembly line where a separate person does each step in the process of making a product, your cells use a separate gene to take care of each step in the chemical process for making melanin.
Remember, a gene is a recipe for making a specific protein. Making melanin requires lots of special proteins called enzymes. Enzymes are just proteins that can bind to a chemical or protein and make a chemical reaction happen. They're the workers in the assembly lines of your cells.
A mutation can happen in the gene coding for any one of the enzymes involved in making melanin, leading to the enzyme not doing its job. Depending on how far into the process of making melanin that enzyme is, the end product will be different.
Imagine an assembly line for a toy truck. If the person who puts the wheels on didn't do his job, then the truck wouldn't be able to roll. But if instead further down the line the person who paints the truck doesn't do her job, the truck would still roll but not be the usual color. The same thing can happen in the pathway to make melanin -- depending on which enzyme is missing, the end product melanin can be changed in different ways.
The red hair in African people is caused by a mutation in a gene called TYRP1. The protein made by this gene is thought to be involved in bringing together all the enzymes needed to make brown melanin. So redheads of African descent completely lack brown melanin and are therefore albino.
But what about red haired Caucasians? Are they albinos too?
Well, no. The red hair in Caucasian people is caused by a mutation in a gene called MC1R that is involved in determining the balance of two variations of melanin in the body. They end up with more of what can be thought of as "the red kind" than "the brown kind." They are not albinos because they still make some of both kinds of melanin.
Redheads are pretty rare in both Caucasian and African populations, but why? Is there a reason certain genetic characteristics would be rare?
A rare genetic trait is often one that is hurtful in some way that gets weeded out of the population. But the redheaded people you see all around you are happy, healthy people. It doesn't seem like their hair color is hurting them. In fact, it's kind of cool!
The thing is that these days, having red hair and light skin can't really hurt you because we spend a lot less of our time outside than our ancient ancestors did, and we have modern day conveniences like sunscreen. But 100,000 years ago when the first humans were evolving, things were a lot different.
Our ancestors most likely first developed in Africa where the sunlight is really strong, so they needed the protection that comes from darker skin. Red hair and light skin would have been very unhealthy, so it was selected against. As people moved farther north, the sun's rays were less intense and they could afford to have mutations in their melanin system that gave them lighter skin and hair. That's probably how we got the Caucasian red heads we have today who so often trace their roots to Northern Europe.
Groups who stayed in Africa would have still had some people with melanin mutations who survived and passed this trait on to future generations. That's how there are modern day Africans with red hair. It just turns out that the most common mutation that stayed in the African population is different than the one that traveled north, and that's why the African redheads are different from the Caucasian redheads.