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St. Bernards Offer Case Study in Speedy Evolution

Jennifer Viegas, Discovery News

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Oct. 24, 2007 -- There may be no more familiar case study in the power of genetic selection to diversify a single lineage than the dog. And, as a new study of St. Bernards has shown, the standards established by breeders can dramatically change a single breed in a short time period.

International breed standards first established in the late 19th century for St. Bernards have resulted in major body changes, especially to the skull, the study found.

The researchers believe their findings illustrate the power of selection -- in this case artificial as opposed to natural.

"It's a model case for evolution," co-author Christian Klingenberg told Discovery News. It's also evidence that humans can guide the process at lightning speed, compared to nature.

By selecting and mating individuals with certain desired qualities, breeders ensure the offspring will be more likely to have those same characteristics. Over generations of that so-called artificial selection, an entire population of animals -- or crops, for that matter -- can change.

The same thing happens in nature, though it's the competitive pressure to survive and reproduce that "selects" for certain characteristics, and it tends to happen much more slowly.

In the case of St. Bernards, if natural selection had favored the same qualities selected by breeders, the changes seen in just over a century would have taken anywhere from 4,000 to millions of years to evolve, according to the study.

Klingenberg, a University of Manchester biologist, and colleague Abby Drake chose to study St. Bernards because Swiss breeders over the years have donated skulls of their deceased St. Bernards to the Natural History Museum in Berne.

While all dogs are believed to have emerged from a common wolf ancestor at least 15,000 years ago, the origins of the St. Bernard date to the 1600's, when monks brought cow-herding dogs to aid lost or distressed mountaineers near their monastery at Great Saint Bernard Pass in the Swiss Alps.

"Originally the dogs varied substantially in size, with some being quite large and others being smaller," Klingenberg said. "After the breeding standards were established, there was debate as to whether or not the dogs should be selected for better rescue skills or for looks, bulkiness and large size. The latter won out."

Supported by the Leverhulme Trust and the Albert Heim Foundation, the biologists analyzed 47 adult St. Bernard skulls dating from 1885 to 2001. They captured three-dimensional coordinates for 64 cranial landmark spots, and then compared these positions and angles to random ones generated by a computer simulator.