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The budding yeast Saccharomyces cerevisiae is used worldwide as a microbial agent for fermented food and alcoholic beverage production with a domestication history of nearly 10 thousands of years.It is also a most-used model system in eukaryotic genetics,genomics and molecular biology.However,the genetic diversity and evolutionary history of the wild and domestic populations of the species remain elusive.Here we show the surprising diversity of S.cerevisiae in both wild and domestic environments and the evolution of the species from primeval forests towards fermentation environments.Phenotypic characterization showed that domestic lineages possess improvedsugar utilization and stress tolerance abilities,suggesting adaptive evolution of the species due to domestication.Comparative genomic analysis recognized genomic and gene network evolution in S.cerevisiae from the wild towards domestication.The wild populations are usually homozygous while the domestic ones are mostly heterozygous,suggesting that the latter were formed by outbreeding between different wild populations and thus gained heterosis,which is then remained by cloning reproduction due to the loss of sexual reproduction ability.The populations associated with dough and grain fermentation possess duplicated maltose transporter(MALx1)gene,resulting in their promoted maltose utilization ability.The S.cerevisiae population associated with spontaneous milk fermentation showed an accelerate galactose utilization rate,probably due to the interaction of the yeast with lactic acid bacteria,which are also dominant in the habitat.The milk fermenting S.cerevisiae strains have relieved from the glucose repression effect.They have duplicated galactose transporter(GAL2)gene and a set of significantly diverged galactose metabolic enzyme genes(GAL1,GAL7 and GAL10)with only 76-77%sequence identities to those of other S.cerevisiae populations.The GAL gene cluster in the milk yeast swains originated by introgression(or horizontal gene transfer)from an unidentified source.