Insights into the genetic code of pigs that reveal how the species evolved could improve the health of animals in future. Researchers compared the genome or genetic make-up of domestic pigs with those of wild boars - from which domestic pigs are descended. Their study found significant genetic differences between wild boars from Asia and Europe, which split from a common ancestor around a million years ago.

These differences are also reflected in the genes of current day Western and Chinese breeds of domestic pigs, confirming the theory that pigs were independently domesticated in each region.

The scientists identified about 21,000 genes in the pig genome and compared these genes to their counterparts in people, mice, dogs, horses and cows.

These comparisons revealed that the immune response genes associated with fighting infection are evolving rapidly. Improved understanding of how these genes have evolved could help combat disease and improve pig health, scientists say.

Their findings also revealed several instances where pig genes resembled a human gene associated with disease, such as diabetes, obesity and Alzheimer's. These discoveries extend the potential of pigs to shed light on human diseases.

The study, published in the journal Nature, was led by scientists at The Roslin Institute at the University of Edinburgh and the Wellcome Trust Sanger Institute, Wageningen University and the University of Illinois.

The analysis also showed that of all mammals whose genetic make-up has been decoded, pigs have the most genes linked to smell.

Scientists say that this is consistent with the known importance of smell to pigs and could explain the pig's ability to hunt for truffles.

Professor Alan Archibald, of The Roslin Institute at the University of Edinburgh, said: "Pork is the most popular of all meats to eat and with a growing global population we need to improve the sustainability of food production. The improved knowledge of pigs' genetic make-up should help us breed healthier and more productive animals."

Professor Lawrence Schook, of the University of Illinois, said: "The new analysis has important implications for agriculture, particularly since the domestic pig still has an ancestor-like wild cousin on the loose. Unlike the domestic cow, whose ancestors, the aurochs, are now extinct, the porcine lineage has a lot of genetic diversity remaining. We can easily find genes that might be still in the wild that we could use for breeding purposes today."

Professor Martien Groenen, of Wageningen University, said: "This study marks the beginning of the sequencing of the genomes of hundreds, perhaps even thousands of individual pigs. This knowledge will be invaluable for pig breeding and exploring fundamental questions in biology and evolution."

The study involved more than 40 institutions in 12 countries. It was funded by the United States Department of Agriculture, the European Commission, the Biotechnology and Biological Sciences Research Council, The Wellcome Trust as well as pig industry groups in Europe and the United States.