Hoofprints in Time
Recent genetic research has answered some long-running questions about the ancient origins of the humble cow. At the time when the first civilisations were being born great floods of cattle surged across the continents. The results of these prehistoric migrations may now help save modern European herds.
The ancestor of all 1.3 billion of today’s cows is the wild ox, or auroch, as seen being hunted by stone-age men in the cave paintings at Lascaux in France. This horned beast was six feet tall at the shoulder and taming it must have been a formidable task, but doing so turned out to be pivotal in the development of civilisations around the globe. Domesticated cattle provided a reliable source of meat and milk, and strong draught animals allowed intensive agriculture that was vital to support cities. In fact, our adoption of the cow changed the course of human evolution. An abundant dairy supply meant that humans adapted to be able to digest milk throughout their lives, and not just during the first few years after birth.
Archaeologists have thought for a long time that oxen were first domesticated eight thousand years ago in the area that is now Iraq. This region is watered by the Tigris and Euphrates rivers and is known as the Fertile Crescent. Many crop species, such as wheat, barley and pea were domesticated here, and the very first cities arose. It is believed that the auroch was also independently tamed by early civilisations in India and Pakistan.
Modern genetics has now been able to confirm these two claims, and has also made some surprising discoveries of its own. Dr. Daniel Bradley and his team from the Smurfit Institute in Dublin have spent the last decade travelling the length and breadth of the world – from India, to Arabia, to Africa. They collected DNA samples from each breed of cow they came across and returned them to the lab to be analysed.
Organelles called mitochondria exist within every cell to provide energy. DNA within these mitochondria is faithfully passed-on in the egg from mother to child, and is not shuffled before reproduction like other DNA. Mistakes occasionally occur during copying and changes steadily accumulate down the generations. Mitochondrial DNA is therefore very good for tracing the ancestry of breeds as they spread around the globe. If the mitochondrial DNA of two types of ox is very similar then the breeds are closely related, and this allows geneticists to draw up a giant “family tree” of the world’s cows. Scientists also know how quickly these DNA changes accumulate, and so can even calculate how long ago the two breeds diverged. When this family tree is overlaid on a world map showing where each sample was taken from something startling becomes obvious.
The oldest breeds are in Iraq and India, which confirms archaeologists’ suspicions that cattle were domesticated independently in these two areas. But the Smurfit Institute also discovered a separate domestication in North Africa 3,000 years ago, at a time when the Saharan region was more temperate. Cattle can be seen to have migrated away from these three origins, like ripples on a pond spreading out from a pebble-drop. As Dr Bradley so poetically puts it, “Guided by the signposts of DNA, we have virtually travelled back in time along the genetic stream”. Herds of oxen were driven from Iraq into Europe and Africa. Dr Bradley also found new evidence that Indian cows made it as far as the east coast of Africa, probably along ancient trade routes. These two great tides of DNA converged in Africa, making it an ideal melting pot for genetic diversity.
European cow herds, however, were much more insular and appear never to have interbred with native oxen. “The forebears of European cattle were wholesale importations from the Near East” says Dr Bradley. Thousands of years of selective breeding since then have left the genetic diversity of our herds dangerously eroded. A Friesian may be able to produce twenty-times more milk than its wild ancestor, but it is much less hardy.
The results of this research are not just an academic curiosity. Dairy farmers and breeders may soon need to turn to nomadic tribes on the plains of Africa. Cattle there show much better resistance to disease and insects, and tolerance of hot and dry conditions. These characteristics will become especially valuable as global warming alters Europe’s climate.
Spare a thought then for the eight thousand years of history behind the cow next time you crunch through your morning cornflakes.
This article was entered into The Daily Telegraph & BASF Young Science Writer Award