Over the course of several generations, segments of ancestral DNA get shuffled so that individuals have varying sequences. Some of these segments, however, that haven't been reshuffled are called haplotypes. If a group of individuals shares long haplotypes, that means the sequence arose relatively recently in our human ancestors. The DNA sequence didn't have enough time to get mixed up.

"What they were able to show is that the people who have blue eyes in Denmark, as far as Jordan, these people all have this same haplotype, they all have exactly the same gene changes that are all linked to this one mutation that makes eyes blue," Hawks said in a telephone interview.

It is pretty wicked to think that this all came down to one person who 'switched' and proliferated from that point.

Also that first person (Blue Eyes - Case 0) must have really got a lot of action on those snowy winter nights.

Scientists find that blue-eyed individuals have a single, common ancestor