Change in skin color for the humans who migrated from Africa to Europe was caused by the mutation of one amino acid in a single gene, Penn State University researchers said.

"The mutation explains part of the lingering mystery of how human skin colors evolved during the last 50,000 years as modern humans migrated across the world after leaving Africa. This really calls into question our ideas about race," said Mark Shriver, one of the study's authors.

Previous studies on pigmentation have identified more than 100 genes involved in pigment production. Alterations in some of these genes are associated with disorders such as albinism. However, most of the genes responsible for normal differences in skin pigmentation remained unknown.

The gene, SLC24A5, identified by Keith Cheng and his team, had not been suspected to be involved in pigmentation.

The study was based on the zebrafish, used in genetics because of its similarities with the human genes. In people of European descent, the melanosomes are fewer, smaller, and lighter than those from people of West African ancestry.

Researchers discovered that a certain type of zebrafish, called "golden", also had fewer, smaller, and less heavily pigmented melanosomes than normal fish.

By adding the gene from the normal fish to the golden one, they noticed a change in pigmentation.

"By default, we are all dark-skinned," a Yale professor said.