George Johnson in The New York Times:
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.