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.
References
[1]
Chang, J.T. (1999) Recent Common Ancestors of All Present-Day Individuals. Advances in Applied Probability, 31, 1002-1026. https://doi.org/10.1239/aap/1029955256
[2]
Rohde, D.L.T., Olson, S. and Chang, J.T. (2004) Modelling the Recent Common Ancestry of All Living Humans. Nature, 431, 562-566. https://doi.org/10.1038/nature02842
[3]
United States Census Bureau (2018) Selected Social Characteristics in the United States. Table ID: DP02. https://data.census.gov/cedsci/table?q=Table%20ID%3A%20DP02&g=0400000US16&tid=ACSDP1Y2018.DP02&hidePreview=false
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[9]
Livingston, G. and Brown, A. (2017) Intermarriage in the U. S. 50 Years after Loving v. Virginia. Pew Research Center, Washington DC. https://www.pewsocialtrends.org/2017/05/18/intermarriage-in-the-u-s-50-years-after-loving-v-virginia/
[10]
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Lachance, J. (2009) Inbreeding, Pedigree Size, and the Most Recent Common Ancestor of Humanity. Journal of Theoretical Biology, 261, 238-247. https://doi.org/10.1016/j.jtbi.2009.08.006
[13]
Freire-Maia, N. (1982) Inbreeding: Inbreeding Levels in Different Countries. Social Biology, 29, 69-81. https://doi.org/10.1080/19485565.1982.9988479
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United States Census Bureau (2014) Fertility of Women in the United States. Table 6, Completed Fertility for Women 40 to 50 Years Old by Selected Characteristics: June 2014. https://www.census.gov/data/tables/2014/demo/fertility/women-fertility.html
