We probably gave tapeworm to farm animals

If you catch tapeworm from eating undercooked pork or beef, don't blame your dinner. New research suggests that the ancestors of modern humans caught these parasites about two million years ago, from the game they hunted on the plains of Africa -- and then passed them onto pigs and cattle while domesticating them about 10,000 years ago.

Two million years ago is "much, much earlier than anyone had previously thought", says Eric Hoberg, the parasitologist with the US Department of Agriculture in Beltsville, Maryland, who has reconstructed the evolutionary history of the tapeworm by studying the anatomy of many different species1.

The finding that the ancestors of domestic cows and pigs caught tapeworms from us -- on three separate occasions -- and not the other way round, overturns 50 years of received wisdom, says Hoberg.

"I think this idea has got quite a bit going for it," says Philip Craig, a tapeworm researcher at Britain's University of Salford. "It's likely that as hominids evolved we already had [these tapeworms], perhaps caught from scavenging."

Hoberg and his colleagues believe that their tapeworm family tree also shows us what early humans were eating, and when and where they were eating it. The closest relatives of the tapeworms that we now catch live in African lions and hyenas. These top predators acquire their intestinal freeloaders from antelopes, where the tapeworms spend their youth.

But the findings "might be open to different interpretations" warns Julia Lee-Thorp, an archaeologist at the University of Cape Town, who has studied the diets of prehistoric hominids.

For example, early humans and carnivores might have just lived in the same place, rather than eaten the same food. "Humans can be pretty dirty creatures," says Lee-Thorp. Large carnivores might even have caught their tapeworms from eating early humans -- "hominids were frequently the prey of large cats and hyenas", she adds.

There is evidence that early humans joined the carnivores' club about two million years ago. Some palaeontologists have suggested that a taste for meat, and the stone technology to catch and butcher it, was one of the things that distinguished the genus Homo from the older, more vegetarian Australopithecus .