Washington, January 16 : Researchers at Uppsala University in Sweden say that the prime reason behind the bewildering diversity in coat colour among domestic animals like pigs and dogs, as compared to their wild counterparts, appears to be the act of cherry-picking and actively selecting for rare mutations by humans.

The researchers say that the process, through which humans have actively changed the coat colour of domestic animals, has been going on for thousands of years.

Writing about their study on pigs in the open-access journal PLoS Genetics, the researchers have said that this result is important because it eliminates several other explanations for coat colour changes within domestic animals.

According to them, one alternative idea was that wild type colour was lost because the pressure to remain camouflage was eliminated.

They further state that this kind of change is analogous to the loss of vision in animals that live in complete darkness, such as caves.

Others proposed that the change of colour was a by-product of domestication because some genes control both a trait under strong selection (e. g. behaviour) and colour.

"Our study settles the debate by showing that the prime reason is intentional selection by humans," says lead researcher Leif Andersson.

The researchers focused their study on one of the key genes that controls coat colour in animals, known as melanocortin-1 receptor (MC1R).

Investigated during the study were both wild and domestic pigs from Europe and Asia.

Though there were numerous differences in DNA sequence among the wild boar, none of them altered the protein function, and thus the coat colour remained camouflaged.

The researchers said that the result showed that mutations that do change the MC1R protein are quickly removed from wild populations in order to maintain camouflage colouration.

In domestic pigs, however, nearly all observed DNA changes changed protein function leading to a wide variety of different colours.

When the researchers compared them with the wild-type sequence, they found that some of the domestic MC1R variants differed by up to three consecutive changes, and thus concluded that domestic coat colour variation was not a recent phenomenon.

"We know that the Mesopotamians were keeping track of differently coloured farm animals 5,000 years ago, and our results suggest black and white and spotted pets and livestock may have been around a lot longer than that", said Greger Larson, a Research Fellow at Uppsala University and at Durham University.

As to why early farmers bothered to change the coat of their livestock, the researchers said that it facilitated animal husbandry because it would be easier to keep track of livestock that were not camouflaged.

The researchers said that a second possibility could be that it has acted as a metaphor for the improved characteristics of the early forms of livestock compared with their wild ancestors.

Another possibility is that the early farmers were as amused and as taken with biological novelty and diversity as we are today.

"This study shows how quickly a protein can change under strong selection and how humans have "created" black-spotted pigs by selecting several consecutive mutations that have occurred by a random process," says Leif Andersson. (ANI)