The successive waves of the Covid-19 pandemic are driven by SARS-CoV-2 variants that reached critical detection levels in different parts of the world. But how evolved the Wuhan virus since its detection in December 2019 into the Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Delta (B.1.617.2) and Omicron (B.1.1.529) variants of concern? This is a story of mice and men, of up to 1,000,000 infected cells in one person, where each cell produces between 10⁵ and 10⁶ viral RNAs, of immune-compromised patients, the digestive tract and viral recombination.