Joel E. Myres, Department of Anthropology
Anthropologists studying human diversity and distribution have long recognized that humans are the recipients of two major informational systems; one cultural and the other biological. Both these components of human diversity are inherited by organisms, be they individuals or populations, across spatial and temporal realms, and retain the ability to influence the behavior or continuance of the organism in terms of fitness. Similarly, the biological record can reflect cultural processes or transitions, such as migrations or disease, much as ethnographic studies can identify elements of cultural adoption, such as ideas or practices. In as much as these elements of culture and biology contribute to human development they are simultaneously interdependent mechanisms pertinent to the study of culture and the diversity of man. Biological research such as genetic studies have enabled researchers to investigate relationships between populations and better understand historical processes that influence or shape these relationships. This study reports genetic variation within Quechua villages of north-eastern Peru and provides historical factors that have contributed to these findings.
Mitochondria are cellular organelles with an autonomously replicating genome independent of nuclear DNA. Mitochondrial DNA (mtDNA) has proven particularly useful in population studies because it lacks many of the complexities intrinsic to nuclear DNA. Haploidy, elevated rate of mutation, lack of recombination, and maternal inheritance permit reconstruction of mitochondrial genealogies based solely on maternal lineages. The compilation of this information can have pathological significance in identifying disease patterns associated with human populations (Torroni & Wallace 1994).
Growing familiarity with the mitochondrial genome has prompted numerous studies designed to document world wide genetic diversity and distribution (Excoffier & Langaney 1989, Horai & Hayasaka 1990). Various genetic studies on the mtDNA of New World peoples have identified and reconfirmed the existence of 4 major mitochondrial haplotypes (A, B, C, & D) extant in modern populations (Horai et al 1993, Torroni et al 1993, Schurr et al 1990, Merriwether et al 1994). These four major New World types (AD) are scattered throughout North, Central and South America and are found represented in modern Asian populations as well, although at differing frequencies. This relationship has pointed to Asia as the ancestral home for New World populations. However, additional types have been identified in both ancient and modern samples which may indicate a contribution from other sources not considered major (Stone & Stoneking 1993, Bailliet et al 1994, Matheny et al1995).
In order to better understand the genetic substructure of New World populations and their relationships, samples from numerous locations are necessary. Samples for this study were collected from residents of twelve Quechua villages in the Department of Amazonas, Peru (see Figure 1). All villages are geographically dispersed and represent a diverse sampling in terms linguistic and cultural affiliation despite their proximity to the provincial capital, Chachapoyas. Linguistic and cultural studies, using numerous techniques and considering various traits, support the historical accounts which document the presence of diverse peoples in the Chachapoyas area. This area has an independent history antedating the expansion of the Inca Empire of Tahuantinsuyo, and the subsequent arrival of Spanish Conquerors. Expansion of Tahuantinsuyo altered the demographics of the entire Empire as native populations were removed and relocated, and others were re-introduced into the occupied area. Chachapoyas experienced significant changes because of this policy as portions of the population were removed to the south near Cuzco, and other settlements created with peoples introduced from the southern coast.
Subsequently, Spanish reducciones and the accompanying small pox epidemics further impacted population sizes and composition of villages already struggling as a result of Inca practices. Inspite of the factors that drastically altered or diluted the indigenous identity of the area, including populations displacements and the imposition of spoken Spanish, numerous villages exhibit proficiency in Quechua and still retain indigenous Quechua names. It is believed the present residents of these villages constitute descendants of the original inhabitants of the area as well as those other peoples displaced and relocated from elsewhere in South America during the period of Inca occupation. Villages of relative isolation would be expected to most accurately represent the indigenous populations with minimal admixture from European sources. Sampling from these villages intends to characterize the genetic substructure of the area in order to better understand the extent of the population amalgamation.
Samples were obtained from individuals voluntarily and consisted of several scalp hairs that were deposited and transported in sterile plastic bags. Each participant was photographed and names and ages were recorded. Genealogical information was compiled when available. Many of these individuals are known to be related. This information is pertinent to understanding the distribution and diversity of the mitochondrial types represented in these villages and reported in this study.
mtDNA was isolated from each hair sample and hypervariable regions of the mitochondrial D-loop were amplified using the polymerase chain reaction (PCR). The mitochondrial D-loop was examined because it is particularly informative for populations genetics. This region is hypermutable and known to contain a high degree of variability providing markers used in ascribing mitochondrial type. Amplified fragments were sequenced to determine nucleotide base pair order for comparative purposes. Sequence polymorphisms were used to determine mitochondrial types.
Selected samples were also examined using restriction enzymes (Wu, unpublished data). Mitochondrial type was determined from RFLP analysis according to previously published information and classified into respective types (A-D) according to previously published literature (Bailliet et al 1994).
Genetic analysis verified that, with the exception of three samples all samples could be classified into one of the 4 major types (A-D). Distribution of the four types among villages indicates that no single type is unique to, or confined to, a particular village. However, certain villages produced only limited types. For example, multiple villages contained only two mitochondrial types.
Distribution of mtDNA types as compiled in the aggregate sample indicates a “goodness” of fit similar to expected x’ distribution under an equal distribution model (x’=6.02, d.f.=3, P>O.OOO 1). Further analysis based on mitochondrial type according to village distribution indicates a highly significant deviation from expected (x’=55.2, d.f.=3, P<0.0001). Such profound discrepancies in type distribution indicates an underlying constraint contributing to this observed deviation in type distribution.
Evidence indicates an elevated underlying genetic variability. The historical precedent of population displacement by the Inca Empire in this area of Peru can account for this increased variability. At the village level, reduced variability exists as subsequent generations of geographic isolation and endogamous relations would help maintain and preserve the original types confined to the ancestral geographic location. Dwindling population sizes have similarly contributed to the reduced lineage type within villages as people relocate to larger population centers. The skewed distribution of mitochondrial types based on village, and extent of village affinity for certain mitochondrial types would indicate a considerable degree of isolation and minimal intra-village relations over time. Only through consideration of contemporary and historical records can the interpretation and relevance of the genetic results be fully appreciated.
Future studies will expand the scope of this project by focusing on more populations throughout Peru. By considering the genetics of populations in conjunction with cultural and environmental factors further avenues of research may lead to insights in disease prevention and health maintenance.
References
- Bailliet, G., F. Rothammer, F. R. Carnese, C. M. Bravi, N. 0. Bianchi. (1994). “Founder mitochondrial haplotypes in Amerindian populations.” Am. I. Hum. Genet. 55:27-33.
- Excoffier, L., A. Langaney. (1989). “Origin and Differentiation of Human mtDNA.” Am. I. Hum. Genet. 44:73-85
- Horai, S., K. Hayasaka. (1990). “Intraspecific Nucleotide Sequence Differences in the Major Noncoding Region of Human Mitochondrial DNA.” Am. ). Hum. Genet. 46:828-842.
- Matheny, R. T., S. R. Woodward, 1. Munoz,]. Chacama, M. Rivera, G. Nielsen, N. Chiu, D. Matheny,]. Myres. (1995). “Ancient Human DNA from South America.” Submitted.
- Merriwether, D. A .. F. Rothammer, R. E. Ferrell. (1994). “Genetic Variation in the New World: ancient teeth, bone, and tissue as sources of DNA.” Experientia 50:592-601.
- Schurr, T. G., S. W. Ballinger, Y.-Y. Can, J, A. Hodge, D. A. Merriwether, D. N. Lawrence, W. C. Knowler, K. M. Weiss, D. C. Wallace. (1990). “American mitochondrial DNAs have rare Asian mutations at high frequencies indicating they derived from four primary maternal lineages.” Am. I. Hum. Genet. 46:613-623.
- Stone, A. C .. M. Stoneking. (1993). “Ancient DNA from a pre-Columbian Amerind population.” Am. !. Phy. Anthropol. 92:463-471.
- Torroni, A. Schurr, T. G. Cabell, M. F. Brown, M. D. Nee!.]. V. Larsen, M. D. Smith, M. (1993). “Asian Affinities and continental radiation of the four founding Native American mtDNAs.” Am. !. Hum. Genet. 53:563-590.
- Torroni A., D. C. Wallace (1994). “Mitochondrial DNA Variation in Human Populations and Implications for Detection of Mitochondrial DNA Mutations of Pathological Significance.” !. Bioenergetic Biomem. 26:261 :271.