Barking up the right evolutionary tree

By Anna Tiley

Dogs are thought to be the first animals domesticated by humans, but until now the timing and location of their origin has been hard to pin down. This is due to a messy evolutionary history caused by intense selective breeding, frequent geographical movement and breeding events with wolves.

Previous genetic studies suggest that the modern domestic dog originated in the Middle East and East Asia around 15,000 years ago. However, this conflicts with ancient fossils from Europe and Siberia which date back much earlier.

Research published in Science last week has clarified the origin and timing of the first domesticated dogs to be in Europe around 18,800 – 32,100 years ago. The study compared the DNA sequences of modern dog species, wolves and doglike fossils. The sequences are different to normal DNA as they don’t come from a nucleus, but from a small compartment found within the cell known as a mitochondrion.

Mitochondrial DNA (mtDNA) is more useful for these studies since offspring inherit it straight from their mother, so there is no mixing with the paternal DNA. The fact that mtDNA doesn’t mix makes it easier to track changes back through time.

Comparing the mtDNA of these canines showed that the extant dog species all fall into one of three groups. Each of the three groups was closely related to wolf species found in Switzerland, Ukraine or Sweden. It is therefore highly likely that modern domestic dogs evolved from an ancient European ancestor.

Dog Photo

The researchers were also able to pinpoint the relatedness of the doglike fossils to modern domestic dogs. Some fossils such as the Goyet dog (Belgium, 36,000 years ago) have been previously thought to be ancestors of extant dog species. However, this research showed that these are not ancestors of modern dogs but are probably strange-looking wolves or doglike groups which became extinct.

The paper also calculated the point at which domesticated dogs diverged from their most recent common ancestor. This is the ancestor to all modern dogs from which early dogs split off from at around 18,800 – 32,100 years ago.

This data suggests that dogs evolved before humans switched from being nomadic hunters to settled farmers. Domestic dogs probably started off as wild wolves which ate the remains of animals killed by humans and later helped during hunting.