Hair Color

Do all blonde people share the same blonde ancestor?

-A curious adult from California

June 26. 2012

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.  Blue eyed Europeans seem to have all come from a single ancestor.  And since blue eyes are pretty much unheard of elsewhere, it may be that all blue eyed people in the world share that same ancestor.

This is again different from other traits like being able to drink milk as an adult.  It looks like most Europeans share a common ancestor who could drink milk but Africans who are lactose tolerant have a different ancestor.

Scientists figure these things out by looking at people’s DNA.  If they share the same ancestor, then their DNA should tell them how they get their trait in the same way. 

So if all blonde people shared a common ancestor, then the same DNA difference should lead to blonde hair.  This is not the case.

It seems that Europeans have ended up with blonde hair in a number of different ways.  Note the “it seems.”  The genetics of hair color is still pretty murky in Europeans so drawing any strong conclusions is still a bit risky.

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.  And Europeans do not share this genetic difference.

Hair Color and DNA

As you may have guessed, 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.

Apparently most hair color is too complicated for a single gene though.  In most cases it looks like many genes all work together to give you your final 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 appears to 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 (R93C in the TYRP1 gene) is also not found in Europeans.  This means that this genetic difference arose in an ancestor distinct from the blonde ones in Europe.

In other words, blondes from the Solomon Islands aren’t that way because of a European sailor marooned there hundreds of years ago.  They got their genetic difference the old fashioned way—mutation.

New Traits

One way that new traits can arise in a population is when there is a DNA change 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 (or a cell that will become an egg or a sperm), then it can be passed on.

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 probably what happened in the Solomon Islands.  Someone developed this DNA change and passed it down to his or her kids.

Of course now we have one person and a few descendants that have this difference that leads to blonde hair.  And because the trait is recessive, it will take a few generations for the blonde hair to be seen.  But even then we just have a few people with the genetic difference.

Something had to happen for it to become so common in the Solomon Island population.  That something could be due to some 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 founding members of the islands happened to have the blonde mutation.  Or maybe some catastrophe struck where there were only a few survivors, one of whom happened to have the mutation.  When the island was repopulated from these survivors, blondes would be much more common than before the catastrophe.  In both cases, 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 blonde ancestor.  Blonde hair has appeared at different times and in different ways.

By Dr. Barry Starr, Stanford University

Unlike blue eyed people, not all blondes have the same ancestor.

DNA has the instructions for hair color.

New traits often appear because of mutation.