When Louis Leakey sat down to recount the discovery of what may be the earliest sign of cancer in the genus Homo, the first thing he remembered was the mud. It was March 29, 1932, midway through the Third East African Archaeological Expedition, and it had rained so long and so hard that it took an hour to drive the four miles from the campsite in Kanjera, near the shore of Lake Victoria, to the Kanam West fossil beds. By the time he and his crew had slogged their way through, they were covered with mud, and before long, Leakey, who was just beginning an illustrious career as an anthropologist, was on hands and knees scouring the ground for newly exposed bones.

He was coaxing the remains of an extinct pig from the muck when one of his Kenyan workers, Juma Gitau, walked over with a broken tooth he had just extracted from a cliff side. Deinotherium, Leakey noted, a prehistoric elephantlike creature that roamed Africa long ago. 

Gitau went back to look for more, and as he was scratching away at the cliff face, a heavy mass of calcified clay broke loose. He chopped it with his pick to see what was inside: more teeth, but not Deinotherium. These looked like what a dentist might recognize as human premolars, still set in bone, yet they came from a layer of sediment deposited, Leakey believed, in early Pleistocene time, about a million years ago.

The Kanam mandible quickly became a sensation. “Not only the oldest known human fragment from Africa,” Leakey proclaimed, “but the most ancient fragment of true Homo yet discovered anywhere in the world.” It was, he insisted, a direct precursor of us all.

Like many of Leakey’s enthusiasms, this one proved controversial. Anthropologists remain divided over whether Homo kanamensis, as Leakey called it, was as old as he believed. Some of them have come to consider the specimen a more recent jawbone — mid- to late Pleistocene — that had washed into much older surroundings. Whatever its pedigree or precise age, Kanam Man is no longer considered remarkable for its antiquity but for an abnormal growth on the left side of the jaw.

At the time of the discovery, it had seemed like a bother, detracting from Leakey’s find. He was working in his rooms at St. John’s College at the University of Cambridge, carefully cleaning the specimen, when he felt a lump. He thought it was a rock. But as he kept picking, he could see that the lump was part of the fossilized jaw. He sent it to a specialist on mandibular abnormalities at the Royal College of Surgeons of England, who diagnosed it as osteosarcoma — a cancer of the bone.

Others have not been as certain. As recently as 2007, scientists scanning the mandible with an electron microscope concluded that this was indeed a case of “bone run amok” while remaining neutral on the nature of the pathology.

Hands-on History

I first came across a mention of the Kanam jaw in a history-of-cancer timeline somewhere on the web. That sent me digging into Leakey’s old books and papers, and after several email exchanges, I tracked down the fossil at the Natural History Museum in London, where it had been in storage for decades. As far as I could tell, it had never been on display.

On a spring day I arrived, as previously arranged, at the museum’s staff and researcher entrance on Exhibition Road. The man at the guard desk called ahead to Robert Kruszynski, curator of vertebrate paleontology. He came out to greet me and then led me into the museum’s inner sanctum. Waiting for me on a table by a window was a brown cardboard box he had retrieved from museum storage. The handwritten label identified the contents: M 16509, KANAM MANDIBLE.

M stood for mammal. In the upper right-hand corner of the label were two colored stickers — a red sunlike symbol and below that a blue star — indicating that the specimen in the box had been analyzed at various times by radioassay and X-rays. Mr. Kruszynski carefully removed the lid. Inside was a smaller box, fashioned from balsa wood and cardboard and covered with a glass lid, and inside that was the Kanam jaw.

He placed it on a padded mat, to cushion it from the hard surface of the table. “All yours to look at,” he said, and he went off to search for another fossil I hoped to see: a femur retrieved from an early medieval Saxon grave in Standlake, England, with an enormous growth that had also been diagnosed as a cancerous bone tumor.

I had thought I would be content just glimpsing the Kanam jaw. I never expected to be left alone with it and to be able to hold it in my hand. It was dark brown and unexpectedly heavy and dense. That shouldn’t have been surprising. It was a rock really, petrified bone. Once it had been part of a prehistoric man, or a proto-man. Two yellowed teeth were still in place, and there was a deep hole where the root of another tooth had been.

Just below that, on the left inside curve of the jaw, was the tumor. It was bigger than I had expected, reminding me perversely of a type of candy from my childhood called a jawbreaker.

There was also a slight swelling on the outside of the jaw, and I could understand how people might argue endlessly over whether it was the remnant of a modern chin, as Leakey himself believed, or just part of the tumor. I could see where Leakey had sliced through the mass (some of his colleagues considered this sacrilege) to remove a section for further analysis. I could almost picture the rest of the head, its vacant eyes pleading for relief from inexplicable pain.

Mr. Kruszynski returned half an hour later to see how I was doing with the fossil. “Don’t bring it too close to the edge,” he warned. I suddenly realized that the protective pad on the table was sloping toward my lap and how easily a sudden movement might have sent the Kanam mandible dropping onto the linoleum floor.

In the end, he was unable to find the cancerous femur I’d inquired about. “For another time,” he said. He escorted me back across the barrier to the public portion of the museum. Hundreds of visitors of all ages coursed through the hallways. Some of them inevitably would get cancer, or they would love somebody who did. I wondered if anyone had been there for Kanam Man.

Ancient Oncology

Not much has been written about the obscure discipline of paleo-oncology. Although research had gone on sporadically for decades, the word was introduced only in 1983 when a small group of Greek and Egyptian oncologists (from the Greek onkos meaning “mass” or “burden”) began planning a symposium on human cancer in earlier times. The gathering took place the following year on a voyage to the island of Kos, where Hippocrates was born. What emerged was an elegantly published, sparsely printed little book, Palaeo-Oncology. I felt lucky to find a copy on the Internet for $100. Its 58 pages are bound in a blue cover with gilded print, and below the title is a drawing of a crab. Crab in Greek is karkinos, and Hippocrates, in the fifth century B.C., used the word for the affliction whose Latin name is cancer. It became the root of carcinogen and carcinoma.

Some 600 years later, the ancient physician Galen speculated on the etymology in an old text: “As a crab is furnished with claws on both sides of its body, so, in this disease, the veins which extend from the tumour represent with it a figure much like that of a crab.” The story is repeated in almost every history of cancer.

Very few tumors, however, look like crabs. Paul of Aegina, a seventh-century Byzantine Greek, suggested that the metaphor was meant to be taken more abstractly: “Some say that [cancer] is so called because it adheres with such obstinacy to the part it seizes that, like the crab, it cannot be separated from it without great difficulty.” The word karkinoi was also applied to grasping tools, like calipers.

All but forgotten is a very different derivation from Louis Westenra Sambon, a British expert on parasitology who, before his death in 1931, turned his attention to the study of cancer. There is a parasite, Sacculina carcini, that feasts on crabs in a manner eerily similar to the feasting of a cancerous tumor. The process was described in a 1936 report by pathologist Sir Alexander Haddow to the Royal Society of Medicine:

[I]t attaches itself to the body of a young crab, and casts off every part of its economy save a small bundle of all-important cells. These penetrate the body of the host and come to rest on the underside of the latter’s intestine, just beneath the stomach. Here, surrounded by a new cuticle, they shape themselves into the “sacculina interna,” and like a germinating bean-seedling, proceed to throw out delicately branching suckers which, root-like, extend through every portion of the crab’s anatomy to absorb nourishment. Growing in size, the parasite presses upon the underlying walls of the host’s abdomen, causing them to atrophy, so that when the crab moults, a hole is left in this region corresponding in size to the body of the parasite. Through this opening the tumour-like body finally protrudes and becomes the mature “sacculina externa.”

Long before Galen, disciples of Hippocrates, dining on crabs, may have noticed the similarities between the ways the parasite overtakes its host and the invasion of a cancer.