If blue eyes are regressive (overridden by brown eyes) then, how could millions of north Europeans end up with blue eyes, supposing that blue eyes come from a single mutation?
In: Biology
The answer is that it’s probably completely random. The theory is called [genetic drift](https://www.genome.gov/genetics-glossary/Genetic-Drift#:~:text=Genetic%20drift%20is%20the%20change,D.)
The effects of genetic drift are more pronounced in smaller populations. It’s likely that Northern Europeans are descended from a small population which ended up randomly all having blue eyes.
One of the tenets of genetic drift is that it ALWAYS leads to fixation of one of the alleles given enough time. We can observe this in nature and stimulate it in models, too.
Here’s more reading if you’d like to know more.
https://biology.sdsu.edu/pub/andy/Bohonak2008.pdf
https://www.nature.com/scitable/knowledge/library/natural-selection-genetic-drift-and-gene-flow-15186648/
https://pubmed.ncbi.nlm.nih.gov/11209765/
Latest Answers