Meat-eating – and diseases that come with it – have a long history among our ancestors, suggests a new study of an ancient hominin skeleton. The analysis of 1.5 to 2.8 million-year-old vertebrae of Australopithecus africanus recovered in South Africa reveals signs of a bacterial infection that is normally contracted from eating meat or dairy foods.
“This is the most ancient case of an infectious disease in a hominin,” says Ruggero D'Anastasio, a palaeoanthropologist at State University “Gabriele d'Annunzio” in Chieti, Italy, who diagnosed the skeleton with a disease called brucellosis.
First uncovered in the 1970s in the Sterkfontein caves, not far from Johannesburg, two of the vertebrae belonging to an older male are dotted with visible lesions. One study concluded that this damage was caused by ageing.
However, after collecting X-rays and scanning electron micrographs of the bones, D'Anastasio now contends that brucellosis better explains the lesions.
Brucellosis causes a flu-like illness in humans, but if the bacteria reach muscles and bones, they tend to infect the same spinal vertebrae that are damaged in the Australopithecus bones. Other infections, like tuberculosis, also infect spinal bones, but they tend to be less discriminate and go after other vertebrae. D'Anastasio's team think ageing is an unlikely explanation for the damage for similar reasons.
“I think it's more probable that these lesions could be due to an infectious disease, and I think brucellosis is the most probable infection,” D'Anastasio says.
It's impossible to determine how this individual contracted the disease, but contemporary patterns of infection suggest the bacteria probably came from an ungulate. Humans usually contract the Brucella bacteria from unpasteurised milk and cheese, however zebras, antelope and other South African fauna can carry a species that causes spontaneous abortions, Brucella abortus.
This australopithecine may have acquired brucellosis by eating fetal tissue from a similar animal, D'Anastasio says. “I think the consumption of meat was occasional in Australopithecus.”
A chemical analysis of Australopithecus teeth also supports that conclusion. A team led by Matt Sponheimer, at the University of Colorado in Boulder, analysed carbon isotopes in 3-million-year-old teeth, and found a chemical signature indicative of fruits, leaves and grasses. The team suggest that the grass signature was probably acquired through eating a herbivore.
Meanwhile, other research has suggested that Australopithecus had teeth adapted for meat eating.
However, none of these studies – the latest work included – can definitively determine the importance of meat in the australopithecine diet, says Sponheimer. Many anthropologists contend that meat eating didn't make up the bulk of our ancestor's calories until after the emergence of Homo erectus, roughly 2 million years ago.
Given the opportunity, chimpanzees eat monkeys, bugs, and small forest antelopes. “It would be strange if any of our more recent ancestors were not eating meat to some degree,” Sponheimer says.
Journal reference: PLoS ONE (DOI: 10.1098/rspb.2009.1027)