For over a decade, Kingsley studied the three-spined stickleback, a small fish whose marine ancestors began to colonise lakes and streams at the end of the last Ice Age.
The researchers found that the blonde hair commonly seen in northern Europeans is caused by a single change in the DNA that regulates the expression of a gene named Kit ligand.
"The very same gene that we found controlling skin colour in fish showed one of the strongest signatures of selection in different human populations around the world," Kingsley explained.
Kit ligand encodes a protein that aids the development of pigment-producing cells.
