A theory began to convulse out of these results, a theory so magnificent and powerful that it would explain decades of disparate observations in a single swoop: perhaps src, the precursor to the cancer-causing gene, was endogenous to the cell. Perhaps viral src had evolved out of cellular src. Retrovirologists had long believed that the virus had introduced an activated src into normal cells to transform them into malignant cells. But the src gene had not originated in the virus. It had originated from a precursor gene that existed in a cell—in all cells. Cancer biology’s decades-long hunt had
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