The present invention relates to methods for producing Saccharomyces strains that are capable of growth on xylose as a sole carbon source at a desired growth rate (such as at least one generation per 48 hours), strains made by such methods, and Saccharomyces strains that grow at a growth rate of at least one generation per 48 hours using xylose as a sole carbon source for growth made by non-recombinant methods.