Scientists are starting to get a better picture of the early weeks of the Covid-19 pandemic in China. To better understand this pandemic and prevent the next one, it matters not just how and where the virus jumped to humans but when. But information is scarce, in part because it seems the Chinese government has been withholding crucial data on early cases that could fill in the timeline.
Working around that shortage of data, some scientists are using samples from around the world to construct a sort of genetic genealogy, creating a family tree of the virus. Others are poring over mobility data from cell phones and even records of increased activity at Chinese crematoriums. Some are finding hints that the disease might have been simmering for weeks or months before it was officially acknowledged.
