At some future time, each person alive today will be either an ancestor of everyone or an ancestor of no one. If the global population were unstructured by geography, race, religion and other factors, the time to future common ancestry for present-day humans would be between 33 and 66 generations, or about 1000 - 2000 years. In a structured population, migration and intermarriage are the necessary conditions for global common ancestry. Simulation of random and hierarchical migration models, shows that time to future global ancestry is generally less than triple, and often less than twice, that required for an unstructured population. The models suggest that someone alive today will become a common ancestor of the entire world population by about 5000 CE, or sooner; and that all current humans who are destined to become global common ancestors will be so by about 8000 CE, or sooner. At which time, everybody then alive will have the exact same genealogical ancestors from the present day.