Brown, green, hazel eye colors are variations in the amount on melanin in the iris. This amount can change as one gets older. Babies can have lighter eyes that become darker.

Blue eyes are believed to be caused by an isolated, inherited gene, OCA2. This gene is present in all people that have blue eyes. It disables the production of melanin in the iris.

All blue eyed people are believed to have a common ancestor from 6000 to 10,000 years ago, the first person with blue eyes (originally caused by a random mutation). It’s harmless enough that lots of us have it now.

See [1].

[1] https://www.sciencedaily.com/releases/2008/01/080130170343.h...

huh. So where does the dominant/recessive traits we learn about in high school play into that?

I ask because my niece had blue eyes as a baby. This didn't make any sense because my sister was Indian, our parents were from India, their parents were from .. well I guess now it's Pakistan, but they migrated during the partition.

My sister married a white dude, but still it seemed very unlikely her daughter wouldn't have brown eyes. That's when we found out my grandmother got her education in Europe, and came back pregnant. Apparently divorces at the time were so shameful that it was better to tell your child their parent died.

My nieces eyes are now a bit hazel/blue-green ish. My grandmother passed away not too long after that, and that secret would have died with her, if it wasn't for the fact that my niece had blue eyes.

Not sure where your question comes from - one common ancestor could nonetheless have had a recessive trait (though selection for it might not kick in until it was visible.) It's not directly relevant, but I might mention there are many sorts of genetic combos/phenotype patterns, not just plain recessive and dominant.

It's likely not harmless but very positive to spread so quickly. I think one hypothesis is the domestication of dogs. They don't usually track fingers, but they do track eyes and having blue eyes may help there. There are many types of melanin - I believe the gene only cuts out one kind.