Do all blonde people have a common ancestor?
A curious adult from California asks:
“Do all blonde people share the same blonde ancestor?”
No, they don’t. Blonde hair seems to have appeared more than once in humans. Which means that different blondes trace back their blonde hair to different ancestors.
This is actually true of a lot of different traits. For example, red hair appears to have come from many different ancestors. The same is true for some serious diseases like cystic fibrosis.
But not every trait is like this. Humans with blue eyes seem to have all come from a single ancestor, for example.
Scientists figure these things out by looking at people’s DNA. If a group of humans share the same ancestor, then their DNA will show that they get their trait in the same way.
If all blonde people shared a common ancestor, for example, then they would all have the same DNA difference that leads to blonde hair. But this is not the case!
It seems that Europeans ended up with blonde hair in a number of different ways. But note the “it seems.” The genetics of hair color is still pretty murky in Europeans, so we can’t draw any strong conclusions just yet.
The same is not true for the 5-10% of people on the Solomon Islands who have blonde hair. There is an obvious and distinct genetic difference that leads to their blonde hair.1 And Europeans do not share this genetic difference.
Hair Color and DNA
Your DNA has the instructions for making and running you. These instructions are found in the form of genes. And each gene has the instructions for one small part of you.
However, most hair color is too complicated for a single gene. In most cases it looks like many genes all work together to give you your hair color.
What this means is that there are many different combinations of genes that can lead to a certain hair color. Which also means not all people with the same hair color came from a single ancestor.
An exception to this rule is blonde people from the Solomon Islands. Their blonde hair all seems to share a common genetic difference. So the most likely explanation is that they all share the same blonde ancestor.
This genetic difference (a mutation in the TYRP1 gene) is also not found in Europeans. This means that this genetic difference arose in an ancestor distinct from blonde humans in Europe.
In other words, people from the Solomon Islands aren’t blonde because of a European sailor who marooned there hundreds of years ago. They got their genetic difference the old fashioned way — through mutation.
One way that new traits can arise in a population is when there is a DNA change, or mutation, that gets passed to the next generation. There are lots of ways to generate these mutations.
Sometimes a cell makes a mistake when it is copying its DNA or DNA gets damaged from chemicals, radiation, or some other agent. If that mistake is in an egg or a sperm cell, then it can be passed on to a person’s offspring.
Imagine that this mistake is in the TYRP1 gene. It changes a C to a T at a certain position and this results in a person having blonde hair. We now have our blonde ancestor.
This is what happened in the Solomon Islands. Someone developed this DNA change and passed it down to his or her children.
Of course now we have one person and a few descendants that have this difference that leads to blonde hair. But even then we just have a few people with the genetic difference.
Something had to happen for blonde hair to become so common in the Solomon Island population. That something could be due to an advantage of having blonde hair, or simple luck.
If blonde hair had an advantage, then blondes would have more kids than darker haired people. Over time, their numbers would increase.
Alternatively, it could be that one of the few founding members of the islands happened to have the blonde mutation. When the island was populated by these founders, blondes would become common just by chance. In this case, blondes would make up a significant part of the population even without an advantage.
So there you have it. All blondes do not share the same common ancestor. Blonde hair has appeared at different times and in different ways in the human population.
Author: Dr. D. Barry Starr
Barry served as The Tech Geneticist from 2002-2018. He founded Ask-a-Geneticist, answered thousands of questions submitted by people from all around the world, and oversaw and edited all articles published during his tenure. AAG is part of the Stanford at The Tech program, which brings Stanford scientists to The Tech to answer questions for this site, as well as to run science activities with visitors at The Tech Interactive in downtown San Jose.