The Known: Cancer Is Really, Really Old. The Unknown: How Common It Was.

Evidence of a cancerous tumor was found on a bone fossil dating back 1.7 million years.

Carcinogens abounded 1.7 million years ago in Early Pleistocene times when a nameless protohuman wandered the South African countryside in what came to be known as the Cradle of Humankind.

Then, as now, ultraviolet radiation poured from the sun, and radon seeped from granite in the ground. Viruses like ones circulating today scrambled DNA. And there were the body’s own carcinogens, hormones that switch on at certain times of life, accelerating the multiplication of cells and increasing the likelihood of mutations.

That, rather than some external poison, was probably the cause of a bone tumor diagnosed as an osteosarcoma found fossilized in Swartkrans Cave, a paleoanthropological trove northwest of Johannesburg. A paper in the current South African Journal of Science describes the discovery, concluding that it is the oldest known case of cancer in an early human ancestor.

“The expression of malignant osteosarcoma,” the authors wrote, “indicates that whilst the upsurge in malignancy incidence is correlated with modern lifestyles, there is no reason to suspect that primary bone tumours would have been any less frequent in ancient specimens.”

Perhaps the main reason there is more cancer today is that people live much longer, leaving more time for dividing cells to accumulate genetic mistakes. Osteosarcoma, however, occurs most frequently in younger people, as their limbs undergo adolescent spurts of growth. That and the fact that bones outlast softer organs make osteosarcoma a natural cancer to look for among early hominins, the zoological tribe that includes humans and their extinct kin.

As I read about the Swartkrans find, I thought of the previous record-holder for oldest humanoid cancer, Kanam Man, a possible victim of osteosarcoma who lived in East Africa perhaps 700,000 years ago. All that we have of Kanam Man (or woman or girl or boy; the gender and age at death are unknown) is a tumorous jawbone.

Decades after its discovery by Louis Leakey in 1932, the fossil’s antiquity and provenance have remained in dispute, along with the medical diagnosis.

Some researchers have attributed the tumor to a different cancer, Burkitt lymphoma, which is endemic in parts of Africa, or to a bone infection called osteomyelitis. Three years ago, after I wrote about the Kanam mandible and other ancient cancer cases in an article for Discover magazine, I heard from a dentist in Seattle who was confident that the tumor was a benign growth called a submandibular exostosis, which he had seen in his own patients.

In the case of the Swartkrans find, the specimen consists only of a foot bone. Again, the gender and precise identity cannot be determined. Homo ergaster and Paranthropus robustus have been found in the same stratum of the cave.

But diagnostic techniques have advanced since the first reports on Kanam Man. The Swartkrans tumor was initially described, in a doctoral thesis, as a benign growth called an osteoid osteoma. A scanning technology called microfocus X-ray computed tomography told a different story. After other diagnoses were considered and discarded, the strongest case was for osteosarcoma.

When you consider the biology of cancer, it is no surprise to find it in early hominins or any form of multicellular life. The oldest known example may be a metastatic bone cancer in a Jurassic dinosaur. (A slice of its skeleton was found by a keen-eyed doctor in a Colorado rock shop.) Errors in cellular division are inevitable and can lead to the development of a malignant tumor. Carcinogens and inherited genetic defects add to the risk.

A more difficult question is how much cancer there was in earlier centuries, compared with modern times. Almost six years ago, two Egyptologists made headlines with a paper in the journal Nature Reviews: Cancer concluding that “a striking rarity of malignancies” in the anthropological record suggests that cancer is “limited to societies that are affected by modern lifestyle issues such as tobacco use and pollution resulting from industrialization.”

That plays right into dystopian visions of cancer as a horror inflicted by a civilization gone amok. But other researchers, considering the same anthropological data, have rejected this view. In 2006, scientists studied the bones from two ancient Egyptian burial sites, dating to 3200 B.C., and a German ossuary, where bodies were deposited between 1400 and 1800 A.D. Those researchers concluded that cancer rates, adjusted for longevity, have probably held steady for centuries.

The seemingly small number of malignant tumors reported by anthropologists is probably an illusion. The only cancers that can be found in long-decomposed remains are those that originated in the skeleton or somehow left a mark there. They include cancers that spread from other organs or, like myeloma, could scar the skeleton in other ways. For most ancient cancers, the evidence rots away. Mummified bodies are rare, but here, too, an occasional cancer has been found.

If all of science’s excavated bones were examined as assiduously as the Swartkrans specimen, many more cases would probably emerge. All we can ever see is the tip of the iceberg.

The Swartkrans discovery was not far from Rising Star, a cave where the remains of at least 15 members of a new species, Homo naledi, were discovered in 2013 in what some anthropologists see as evidence of prehuman burial rituals. I wondered if any of them died from cancer.

“We don’t have anything to report on pathology from these fossils yet,” John Hawks, a senior member of the expedition, told me. “Some really interesting aspects of health leave only very subtle traces on bone, so we can’t definitively rule anything out.”

In any case, the odds of a find are low, no matter how prevalent cancer was. Today, the incidence rate for all bone and joint cancers is nine cases for every one million people. Barring good luck, one would have to scan a vast number of skeletons to find a single example.

Throughout the Cradle of Humankind, Dr. Hawks estimated, there are about 2,800 fossil specimens. “I believe we are looking at the remains of fewer than 150 individuals,” he said.

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