Cancer's roots lie deep in prehistory. Swartkrans cave, a rich archaeological site, has yielded a 1.7 million-year-old foot bone with a malignant tumor -- the oldest evidence of cancer yet discovered by scientists.

Researchers identified the tumor as osteosarcoma, an aggressive bone cancer found in young people among modern adults. The ancient foot, however, did not belong to a modern adult.

Scientists believe the owner of the diseased foot was an early human relative, a bipedal hominin, but can't determine the exact species.

At the nearby site of Malapa, scientists found evidence of a benign tumor in the fossilized vertebrae of a Australopithecus sediba specimen. The vertebrae are 2 million years old.

Both discoveries -- detailed in separate papers in the South African Journal of Science -- push back the emergence of both benign and malignant cancers in the human lineage.

"Modern medicine tends to assume that cancers and tumors in humans are diseases caused by modern lifestyles and environments," Edward Odes, a doctoral candidate at the University of Witwatersrand's Evolutionary Studies Institute, said in a news release. "Our studies show the origins of these diseases occurred in our ancient relatives millions of years before modern industrial societies existed."

Previously, the earliest evidence of a hominin tumor was credited to a 120,000-year-old Neanderthal fossil.

Researchers used CT scans to diagnose and describe the two tumors.

While researchers can't say for sure whether the foot belonged to a child or adult, or whether the cancer was the cause of death, the vertebrae with the benign tumor belonged to a child.

"Not only has there been an assumption that these sorts of cancers and tumors are diseases of modernity, which these fossils clearly demonstrate they are not, but that we as modern humans exhibit them as a consequence of living longer, yet this rare tumor is found in a young child," explained Wit professor Lee Berger. "The history of these types of tumors and cancers is clearly more complex than previously thought."