Scientists in the United States have discovered what they believe is the gene that helps determine whether a human has dark or light coloured skin.
In an article published in the journal Science, a team from Pennsylvania State University said two variations of the same gene strongly influence skin pigmentation.
The researchers reported that according to their findings 99 per cent of the population of Europe has one version of the gene SLC24A5.
In Africa, between 93 and 100 per cent of the population have the other type.
According to the main author of the article, Keith Cheng, the discovery has revealed important insights into the evolution of skin colour in human beings.
In an accompanying article also published in Science, the Australian molecular biologist Richard Sturm described the discovery as absolutely original and pioneering'.
According to the researchers' work, our ancestors developed dark skin one and half million years ago as the amount of hair on their bodies reduced.
Dark pigmentation protects skin from harmful ultraviolet rays emitted by the sun.
Ultraviolet destroys vitamin B folic acid in the body which can lead to a number of serious health problems and in some cases to birth defects.
But in climates with relatively little sunshine, dark pigmentation also prevents important chemical processes that take place in the skin such as vitamin D production.
So as humans migrated to colder climates in the north it became important for skin to evolve to adapt to changing conditions.
Cheng and his colleagues identified the colour gene for the first time in a rare breed of zebrafish.
They examined the genetic code of a variety of zebrafish that had lighter coloured stripes as well as a golden pigmentation than the common version.
They concluded a gene that influences the melansomes - granules that make the pigment melanin - in the skin caused the difference between the two types of fish.
The equivalent gene in humans is SLC24A5. It causes melansomes to either grow in size and clump together causing dark skin, or to shrink and the space between the particles to increase in light coloured skin.