Genetic perspectives on prehistoric social practices
Brigitte PakendorfMPI 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
• Holds especially true for social practices that affect one of the sexes more than the other: polygyny, residency patterns, ‘upward’ social mobility
Benefits of mtDNA and Y chromosome
• exclusively maternal and paternal inheritance, respectively
• no recombination
The benefits of studying mtDNA and Y-chromosomal markers:
Y(non-sex) chromosome
mtDNA
Y-chromosome
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
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
Socially conditioned prehistoric events
1. Residence patterns
2. Sex-biased migrations
3. Polygamy
4. ‘Upward’ social mobility
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
Oota et al. (2001) Nature Genetics 29: 20 - 21
Genetic diversity in Thailand hill tribes
Melanesian mtDNAAsian mtDNAOther mtDNA
2) Sex-biased migrations: Pacific
Kayser et al. (2006) Mol Biol Evol. 23: 2234-44.Map courtesy of the University of Texas Libraries, The University of Texas at Austin.
Melanesian Y-DNAAsian Y-DNAOther Y-DNA
2) Sex-biased migrations: Pacific
Kayser et al. (2006) Mol Biol Evol. 23: 2234-44.Map courtesy of the University of Texas Libraries, The University of Texas at Austin.
Polynesian mtDNA: 94% Asian origin
2) Sex-biased migrations: Pacific
Polynesian Y: 66% Melanesian origin
Potentially due to matrilocality of Austronesian- speakersMelanesian men incorporated into Austronesian- speaking society prior to further migration to Polynesia
Kayser et al. (2006) Mol Biol Evol. 23: 2234-44.
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
2) Sex-biased migrations: male conquerors
Zerjal et al. (2003): Am J Hum Gen. 72: 717–721
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
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
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
3) Polygamy (polygyny)
• Polygyny: few men have many wives, and many men may have no wife at all
• Prediction: (severely) reduced Y-chromosomal diversity
Kayser et al. (2003): Am J Hum Genet 72:281-302
Y-chromosomal SNP frequencies in New Guinea
Y-chromosomal and mtDNA diversity, West New Guinea
Group (N Y/ N mtDNA)
Y-SNP diversity
Y-STR diversity
HVR1 diversity
Dani (12/21) .167 ± .134 .455 ± .170 .98 ± .02
Una (46/50) 0 .749 ± .061 .96 ± .01
Ketengban (19/22)
0 .608 ± .127 .81 ± .07
Citak (28/39) .267 ± .107 .860 ± .056 .92 ± .03
Kayser et al. (2003): Am J Hum Genet 72:281-302
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)?
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
Upward social mobility
‘Khoisan-specific’ haplogroups
mtDNA L0d Y-chr. A-M51
Southern African Bantu speakers
Southern African Bantu-speakers
Upward social mobility
‘Khoisan-specific’ haplogroups
mtDNA L0d Y-chr. A-M51
Southern African Bantu speakers
4-7%
Southern African Bantu-speakers
Pereira et al. (2001): Ann Hum Genet 65: 439-458 Salas et al. (2002): Am J Hum Genet. 71: 1082–1111
Upward social mobility
‘Khoisan-specific’ haplogroups
mtDNA L0d Y-chr. A-M51
Southern African Bantu speakers
4-7%
Southern African Bantu-speakers
3-7%
Pereira et al. (2001): Ann Hum Genet 65: 439-458 Salas et al. (2002): Am J Hum Genet. 71: 1082–1111Wood et al. (2005): Eur J Hum Genet 13: 867-876
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
Upward social mobility
‘Khoisan-specific’ haplogroups
mtDNA L0d Y-chr. A-M51
Southern African Bantu speakers
4-7%
Southern African Bantu-speakers
3-7%
Pereira et al. (2001): Ann Hum Genet 65: 439-458 Salas et al. (2002): Am J Hum Genet. 71: 1082–1111Wood et al. (2005): Eur J Hum Genet 13: 867-876
Upward social mobility
‘Khoisan-specific’ haplogroups
mtDNA L0d Y-chr. A-M51
Mozambique Bantu speakers
4-7% ??
South Africa Bantu-speakers
?? 3-7%
Pereira et al. (2001): Ann Hum Genet 65: 439-458 Salas et al. (2002): Am J Hum Genet. 71: 1082–1111Wood et al. (2005): Eur J Hum Genet 13: 867-876
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)
Patrilocality in Bantu-speakers?
• Prediction: in patrilocal groups, mtDNA diversity should be higher than Y-chromosomal diversity
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: 867-876Quintana-Murci et al. (2008): PNAS 105: 1596–1601; De Filippo et al. unpublished
West CentralAfrica
NgumbaTuru
SukumaBisa
KundaSouthern
Africa
Y-chromosome
mtDNA
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Y-chromosome
mtDNA
Social practices of Bantu-speaking groups?
• Reduced Y-chromosomal diversity appears indicative of patrilocal post-marital residence
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
Data are not comparable
• practically no comparable data available for mtDNA and Y-chromosome in the same Bantu-speaking groups
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
Acknowledgements
• Cesare de Filippo for Bisa and Kunda data• Mark Stoneking for discussion