Tuesday, 23 July 2013

Cancer since prehistoric time

The idea that cancer is a modern disease is a common misconception — one that the fossil record reveals to be untrue.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.


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