Many early domestic dogs ate almost no meat. Dogs living around 3000 years ago in what is now Spain were instead fed cereals, such as millet, by their owners.
Although the diet may reflect the fact that meat was relatively scarce among human societies at the time, feeding dogs with cereals could have been advantageous, says Silvia Albizuri at the University of Barcelona in Spain. It may have been a way to ensure the dogs had plenty of energy for the strenuous work of herding and guarding livestock, she says, particularly since these dogs 鈥渨ere not pets as we conceive them nowadays鈥�.
Dogs were domesticated from wolves in Europe and Asia within the past 40,000 years. Wolves are carnivores, getting most of their nutrition from meat.
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Albizuri and her colleagues studied the remains of 36 dogs from Can Roqueta, an archaeological site near Barcelona. It lies on a plain near the coast and was inhabited from the Stone Age onwards. The dogs lived in the Bronze Age and Iron Age, between 1300 and 550 BC, and had been buried in pits.
The researchers obtained protein from the dogs鈥� bones and focused on the carbon and nitrogen atoms in the samples, each of which exist in two forms called isotopes. Different foods have varying ratios of carbon and nitrogen isotopes, and this influences the makeup of the protein 鈥� so studying the isotopes in the protein gives an indication of what the animals ate.
The dogs鈥� diets differed considerably. While nine of them ate plenty of meat and 10 were omnivorous, the rest ate mostly plants 鈥� and some had isotope ratios that could barely be distinguished from those of the cattle they once guarded.
The finding adds to the evidence that many early domestic dogs ate little meat, says Albizuri. This trend began with the advent of farming. 鈥淲hen human societies began to domesticate plants during the Neolithic period, hunting decreased and the human diet was based mainly on vegetables,鈥� she says. 鈥淒ogs began to be fed on plants, mainly cereals.鈥�
This has had effects on domestic dogs today, says Albizuri. Grains are easier to chew than raw meat, so they don鈥檛 need their jaw muscles to be as strong as those of wolves. What鈥檚 more, their jaw bones have changed shape and their teeth have shrunk. Their digestive systems have also changed. 鈥淒ogs have more genes involved in starch metabolism than wolves,鈥� she says.
However, not all dogs have undergone these changes. 鈥淪ocieties that maintained a subsistence system based on hunting and gathering, mainly those located in cold areas, continued to feed their dogs with meat,鈥� says Albizuri. 鈥淚n today鈥檚 dog breeds, there are significant genetic differences related to starch metabolism.鈥�
Journal of World Prehistory
