In late December, scientists in California began searching coronavirus samples for a fast-spreading new variant that had just been identified in Britain. They found it, though in relatively few samples. But in the process, the scientists made another unwelcome discovery: California had produced a variant of its own. In December, researchers in Britain found the variant to COVID-19, B.1.1.7, which is about 50 percent more transmissible than previous versions of the virus, and a driving factor in the surge of cases and hospitalizations there now. B.1.1.7 was in the United States in early November, according to a study by University of Arizona biologists including Dr. Michael Worobey, evoluntary biologist and BIO5 associate director. That would mean the variant had been circulating for two months before being detected. Other scientists are also looking more closely at the rise in frequency of the variant in California, searching for evidence that could determine whether biology or chance is to blame for the rise in the presence of the virus.