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Genetic perspectives on prehistoric social practices

Genetic perspectives on prehistoric social practices. Brigitte Pakendorf MPI for Evolutionary Anthropology, Leipzig, Germany. Social practices and genetics?. Social practices can have an effect on the number of offspring a person has  can be detected with genetic methods

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Genetic perspectives on prehistoric social practices

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  1. Genetic perspectives on prehistoric social practices Brigitte Pakendorf MPI for Evolutionary Anthropology, Leipzig, Germany

  2. Social practices and genetics? • Social practices can have an effect on the number of offspring a person has  can be detected with genetic methods • Holds especially true for social practices that affect one of the sexes more than the other: polygyny, residency patterns, ‘upward’ social mobility

  3. Benefits of mtDNA and Y chromosome • exclusively maternal and paternal inheritance, respectively • no recombination

  4. The benefits of studying mtDNA and Y-chromosomal markers: mtDNA Y (non-sex) chromosome Y-chromosome

  5. Benefits of mtDNA and Y chromosome • mutations accumulate with time alone • possibility of defining related lineages (= haplogroups), i.e. shared mutations indicate shared ancestry (if mutations are rare!!) • complementary studies of population history (female vs male) are possible

  6. Types of mutations • SNPs = Single Nucleotide Polymorphisms – individual base changes (e.g. T  C):slow mutation rate • STRs = Short Tandem Repeats – change in number of repeat sequence of bases (e.g. [AGCT]16 [AGCT]17):very high mutation rate

  7. Socially conditioned prehistoric events • Residence patterns • Sex-biased migrations • Polygamy • ‘Upward’ social mobility

  8. 1) Residence patterns • Matrilocality: the groom settles with the wife’s family after marriage  mixing of Y-chromosomes, mtDNA’s stay put • Patrilocality: the bride settles with the husband’s family after marriage  mixing of mtDNA’s, Y-chromosomes stay put • Prediction: in patrilocal groups, mtDNA diversity should be higher than Y-chromosomal diversity, and vice versa for matrilocal groups

  9. Genetic diversity in Thailand hill tribes Oota et al. (2001) Nature Genetics 29: 20 - 21

  10. 2) Sex-biased migrations: Pacific Melanesian mtDNA Asian mtDNA Other mtDNA Kayser et al. (2006) Mol Biol Evol. 23: 2234-44. Map courtesy of the University of Texas Libraries, The University of Texas at Austin.

  11. 2) Sex-biased migrations: Pacific Melanesian Y-DNA Asian Y-DNA Other Y-DNA Kayser et al. (2006) Mol Biol Evol. 23: 2234-44. Map courtesy of the University of Texas Libraries, The University of Texas at Austin.

  12. 2) Sex-biased migrations: Pacific Polynesian mtDNA: 94% Asian origin Polynesian Y: 66% Melanesian origin • Potentially due to matrilocality of Austronesian- speakers • Melanesian men incorporated into Austronesian- speaking society prior to further migration to Polynesia Kayser et al. (2006) Mol Biol Evol. 23: 2234-44.

  13. 2) Sex-biased migrations: male conquerors • Closely-related Y-chromosomal lineage identified in 16 Central Asian populations Zerjal et al. (2003): Am J Hum Gen. 72: 717–721

  14. 2) Sex-biased migrations: male conquerors Zerjal et al. (2003): Am J Hum Gen. 72: 717–721

  15. 2) Sex-biased migrations: male conquerors • Closely-related Y-chromosomal lineage identified in 16 Central Asian populations • Dated to ~ 700-1300 years BP • Most likely origin in Mongolia (highest diversity) Zerjal et al. (2003): Am J Hum Gen. 72: 717–721

  16. 2) Sex-biased migrations: male conquerors Distribution of Mongolian Y-chromosomal lineage; shaded area = extent of Mongol Empire at time of Chinggis Khan’s death Zerjal et al. (2003): Am J Hum Gen. 72: 717–721

  17. 2) Sex-biased migrations: male conquerors • Y-lineage with one male ancestor ~ 1000 years ago • widespread in Central Asia  spread with Mongol Empire • ruling clans = Chinggis Khan’s sons and grandsons  ‘Chinggis Khan’s Y-chromosome’ Zerjal et al. (2003): Am J Hum Gen. 72: 717–721

  18. 3) Polygamy (polygyny) • Polygyny: few men have many wives, and many men may have no wife at all • Prediction: (severely) reduced Y-chromosomal diversity

  19. Y-chromosomal SNP frequencies in New Guinea Kayser et al. (2003): Am J Hum Genet 72:281-302

  20. Y-chromosomal and mtDNA diversity, West New Guinea Kayser et al. (2003): Am J Hum Genet 72:281-302

  21. Social practices of Bantu-speaking groups? • Can genetic studies inform us about the prehistoric social practices of Bantu-speaking groups (intermarriage with hunter-gathering populations, patrilocality)?

  22. Upward social mobility • Ethnographic assumption: agriculturalist men may marry hunter-gatherer women, but not vice versa • Prediction: introgression of ‘hunter-gatherer mtDNA’ but not Y-chromosomes in agricultural populations

  23. Upward social mobility

  24. Upward social mobility Pereira et al. (2001): Ann Hum Genet 65: 439-458 Salas et al. (2002): Am J Hum Genet. 71: 1082–1111

  25. Upward social mobility Pereira et al. (2001): Ann Hum Genet 65: 439-458 Salas et al. (2002): Am J Hum Genet. 71: 1082–1111 Wood et al. (2005): Eur J Hum Genet 13: 867-876

  26. Upward social mobility • Potentially intriguing finding:1) the social ideal is not always adhered to2) shift of language and identity of small groups of Khoisan-speakers in Southern Africa

  27. Upward social mobility Pereira et al. (2001): Ann Hum Genet 65: 439-458 Salas et al. (2002): Am J Hum Genet. 71: 1082–1111 Wood et al. (2005): Eur J Hum Genet 13: 867-876

  28. Upward social mobility Pereira et al. (2001): Ann Hum Genet 65: 439-458 Salas et al. (2002): Am J Hum Genet. 71: 1082–1111 Wood et al. (2005): Eur J Hum Genet 13: 867-876

  29. Upward social mobility • Caveat: groups not really comparable  South African Nguni populations (Zulus, Xhosa) are known to have been in close contact with Khoisan speakers (‘borrowing’ of clicks)

  30. Patrilocality in Bantu-speakers? • Prediction: in patrilocal groups, mtDNA diversity should be higher than Y-chromosomal diversity

  31. Haplogroup diversity values in some Bantu-speaking groups Tishkoff et al. (2007): Mol Biol Evol 24: 2180-2195; Pereira et al. (2001): Ann Hum Genet 65: 439-458 Salas et al. (2002): Am J Hum Genet. 71: 1082–1111; Wood et al. (2005): Eur J Hum Genet 13: 867-876 Quintana-Murci et al. (2008): PNAS 105: 1596–1601; De Filippo et al. unpublished

  32. Social practices of Bantu-speaking groups? • Reduced Y-chromosomal diversity appears indicative of patrilocal post-marital residence

  33. Data are not comparable • ‘West Central Africa’mtDNA = 20 groups from Cameroon and Gabon Y-chromosome = 3 groups from Cameroon • ‘Southern Africa’mtDNA = ~ 20 different populations from Mozambique Y-chromosome = Sotho-Tswana, Zulu and Xhosa from South Africa

  34. Data are not comparable • practically no comparable data available for mtDNA and Y-chromosome in the same Bantu-speaking groups

  35. Conclusions • Genetic analyses can provide some insights into prehistoric social practices • These may be of help for historical linguists in search of explanations for patterns of linguistic diversity (e.g. contact-induced change) • However, comparable studies of both mtDNA and Y-chromosomal diversity in ethno-linguistically well-defined groups are needed

  36. Acknowledgements • Cesare de Filippo for Bisa and Kunda data • Mark Stoneking for discussion

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