ANNUAL REVIEWS
Further
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Annu. Rev. Genet. 1978.12:365-413. Downloaded from www.annualreviews.org Access provided by New York University - Bobst Library on 02/08/15. For personal use only.
Ann. Rev. Genet. 1978. 12:365-413 Copyright © 1978 by Annual Reviews Inc. All rights reserved
THE POPULATION STRUCTURE
.3143
OF AN AMERINDIAN TRIBE, THE YANOMAMA1 James
V.
Neel
Department of Human Genetics, University of Michigan Medical School, Ann Arbor, Michigan 48109
CONTENTS THE YANOMAMA ...................................................................................................... Unusual Features........................................................................................................ THE POPULATION STRUCTURE OF THE YANOMAMA.................................. Village Size and Location .......................................................................................... Biodemography .......................................................................................................... f.0�mf!l SociaJ �!ructure a�d Inbreeding ................................................................. . ; 'FISsIOn-FusIOn and the 'Lmeal Effect , ................... ............ . ... ..... . ................... .... ''Migration''................................................................................................................ SOME CONSEQUENCES OF THIS POPULATION STRUCTURE ...................... Genetic Microdifferentiation ...................................................................................... Departures from Hardy-Weinberg Equilibrium ........................................................ Clines .......................................................................................................................... Zygotic Disequilibrium .............................................................................................. Fate of a Mutant Gene: to and Founder Effect ........................................................ Random Loss of Variation ........................................................................................ The Potential for Natural Selection .......................................................................... TOWARD AN IMPROVED MODEL FOR TRIBAL POPULATIONS ................ EPILOGUE .......................................................... ..........................................................
367 368 371 371 371 376 378 379 382 382 388 390 394 396
400
401 403 407
'The original research on which this review is based was supported by the Energy Research and Development Administration (now Department of Energy) and the National Science Foundation.
0066-4197/78/1215-0365$01.00
365
366
NEEL
Those from the Western World who attempt to enter into the domain of primitive2 man seem to respond in either of two ways. To some it is a constantly threatening experience, challenging beliefs and assumptions of ten poorly perceived by their holder, an experience best discreetly aban doned at the earliest opportunity. For others it is a privileged experience, carrying with it deeply felt responsibilities. There is, on the one hand, the
Annu. Rev. Genet. 1978.12:365-413. Downloaded from www.annualreviews.org Access provided by New York University - Bobst Library on 02/08/15. For personal use only.
humanistic responsibility that springs from the realization that one is there as a representative of a culture that throughout the world has ruthlessly violated the rights of primitive man. There is, on the other hand, especially for scholars, the scientific responsibility that follows from the sad but indis putable fact that primitive man will soon be no more. Within the next generation our opportunities will be gone to visit ourselves in a reasonable facsimile of the conditions under which the evolution that renders us dis tinctly human has occurred. How often has that thought, and the doubt that I was making the most appropriate observations possible under the circum stances, kept me awake in my hammock on one of those soft tropical nights that so miraculously follow the heat of the day. This review will deal with the attempts of a multidisciplinary team to characterize in some depth the genetic structure of a particular tribe of South American Indians, the Yanomama. This effort is an aspect of a larger program which has thus far resulted in contacts with some With respect to the Yanomama, our field work began in
15 Indian tribes. 1 964, when Dr.
Napoleon Chagnon initiated his anthropological studies. This was followed by a series of 9 eXpeditions to the tribe, the first in
1966,
d
each expedition
0, > 1 00, >400, > 1000 ) at various generations following its appearance, for various values of m. (An m value greater than 1 .0 can be due either to positive selection for an allele or to a generally expanding population in which the allele increases at the same rate as the type allele.) Section A of the table illustrates expectation if the
399
Annu. Rev. Genet. 1978.12:365-413. Downloaded from www.annualreviews.org Access provided by New York University - Bobst Library on 02/08/15. For personal use only.
YANOMAMA POPULATION STRUCTURE
census was from newborn-to-newborn, Section B if from adult-to-adult. In view of the high infant mortality in such populations, the infant-to-infant census is rarely feasible and one will usually base any treatment on the adult generation. The predictions of Table 4 have been checked through 1 6 generations by the above-described computer simulation with very satisfac tory agreement. Thompson & Neel (106) have also considered the conse quences of fluctuating values of m. In most Indian tribes, numbering no more than 2000 adults (aged 1 5-40), 100 copies of an allele would constitute a genetic polymorphism. Table 4 illustrates the great importance of relatively small differences in m to the probability of such a polymorphism. Thus, selecting from the examples of Table 4, the probability of an allele being represented by 100 or more copies Table 4
The probability o f a rare variant exceeding a specified number of copies (0, 1 00,
4 00 , 1 000) at t he given generation (t) wi th various schedules of variant increase p er gen eration (m), in a population with the structure of the Yanomamaa Number of copies >0
> 1 00
A . Simulation m = 0 .98
m = 1 .0
m = 1 .05
m
=
l .l
> 400 c
0 .0242
1 00
4 00
0 . 00 1 3 5 0.0 1 4
16
0 .0296
1 00
0.0049
400
0 .00 1 2
2 0.0 1 5 2 0 .0 3 0 2 0.0 1 1
m
=
=
1 .05
1 .1
a part A of the
7 0.0 1 9 4 0.0 1 1 7 0.0 20 6 0.0 1 8 3 0.0 69 0.0 37 5
0.0
16 8
13
0.0 8 0 0.0 1 0 3 2 0.0
14 4
27
0 . 0 38
0.0 3 3 6
16
0.044 1
0.0 1 3
0 .0 1 0 6 1
1 00
0 .0246
0 .024 1
0.0228
0.0204
400
0 . 0 244
0.0244
0 . 06 1 5
0 .0 1 60
0.0244 0.0 3 2 8
0.0244
16 1 00
0 .048 7
0 .048 7
0.04 8 7
0.0486
400
0.0487
0 .048 7
0.048 7
0.0487
4 0.0 1 1
16
0 .0 8 5 7
1 00
0 .0 1 4 8 0 .0 0 3 7
0 .0 2 3 3 2 0.0 26
4
c =
0.078 7
0 .40 16 0.0 23 4 0.0 38
0.0
8 0.0 5 1 4 0.0 8 8
16
0 . 1 302
3 0 . 0 28
0 .0 3 8 4 11 0.0 27
1 00
0 .0 7 5 5
0.07 1 3
0.0600
0.0425
400
0.07 5 0
16
0 . 1 840
0 . 07 5 0 2 0.0 3 1
0.0750 7 0.0 1 5
0.0750 18 0.0 32
1 00
0 . 1 5 00
0 . 1 498
0 . 1 494
0 . 1 484
400
0 . 1 5 00
0 . 1 5 00
0 . 1 500
0 . 1 5 00
400 m
0 .67
0 .0 2 5 7
B. Ad u It-to-aduIt m = 1 .0
=
3 0.0 7 2 3 0 .0 39 6 0 .0 4 8
16
> 1 000
0.0
27
26
table pertains to the introduction of the variant into a just-born child, in
which case c, the geometric parameter in the ex pression describing the distribution of family size, has a value of 0 . 6 7 . Part B pertains to the introduction of the variant into the population b y a young adult, in which case c has a value of 0.40.
Annu. Rev. Genet. 1978.12:365-413. Downloaded from www.annualreviews.org Access provided by New York University - Bobst Library on 02/08/15. For personal use only.
400
NEEL
at generation 100 is 0.00039 at m = 0.98, but 0.0241 at m = 1 .05. However, given Amerindian tribal sizes, clearly no tribe has experienced m values of 1 .05 or 1 . 10 for very many generations, and the most appropriate perspec tive on founder effect is supplied by the lower m values. The table also illustrates the high probability of mutant loss within a relatively few genera tions, first emphasized by Fisher (99) with a deterministic model, but also demonstrates that contingent upon survival, an allele after 100 generations will, even for small values of m , have close to a 50% probability of emerging as a private polymorphism. The occurrence of a private polymorphism of serum albumin with an allele frequency of 0.076 in the Yanomama has already been mentioned. We estimate 1066 copies of this allele in the adult generation of Yanomama. From Table 4 we see that for values of m less than 1 .0, such a founder effect should be very rare, but for an expanding tribe, relatively much more common. The treatment of Section B of Table 4 is obviously also appropri ate to the introduction of a single unique allele into a tribe by an immigrant.
R andom Loss 0/ Variation The subject of random loss of variation, to which in effect the preceding section was directed, can also be approached in a highly empirical fashion from data on multiallelic systems in the Yanomama. In addition to the various typings already mentioned, the frequency of the HLA haplotypes for the A and B loci have been determined for 2 1 8 persons in 8 Yanomama villages, the number examined per village ranging from 1 5 to 74 (107). The villages in question were in the central portion of the tribal distribution, so that recent admixture with representatives of other tribes was most un likely. There were no blanks (designated Xl) with the battery of antisera employed for typing antigens of the A series but 8. 1 % blanks (designated X2) for typings in the B series. The data suggest the presence of 5 alleles at the A locus and at least 6 at the B locus, the uncertainty arising from the ambiguities implicit in the blank phenotype at the B locus. Figure 4 illustrates the range of gene frequencies encountered in these villages for the HL-A alleles as well as the MNSs, Fj', Rh, and Jk
Further
Quick links to online content
Annu. Rev. Genet. 1978.12:365-413. Downloaded from www.annualreviews.org Access provided by New York University - Bobst Library on 02/08/15. For personal use only.
Ann. Rev. Genet. 1978. 12:365-413 Copyright © 1978 by Annual Reviews Inc. All rights reserved
THE POPULATION STRUCTURE
.3143
OF AN AMERINDIAN TRIBE, THE YANOMAMA1 James
V.
Neel
Department of Human Genetics, University of Michigan Medical School, Ann Arbor, Michigan 48109
CONTENTS THE YANOMAMA ...................................................................................................... Unusual Features........................................................................................................ THE POPULATION STRUCTURE OF THE YANOMAMA.................................. Village Size and Location .......................................................................................... Biodemography .......................................................................................................... f.0�mf!l SociaJ �!ructure a�d Inbreeding ................................................................. . ; 'FISsIOn-FusIOn and the 'Lmeal Effect , ................... ............ . ... ..... . ................... .... ''Migration''................................................................................................................ SOME CONSEQUENCES OF THIS POPULATION STRUCTURE ...................... Genetic Microdifferentiation ...................................................................................... Departures from Hardy-Weinberg Equilibrium ........................................................ Clines .......................................................................................................................... Zygotic Disequilibrium .............................................................................................. Fate of a Mutant Gene: to and Founder Effect ........................................................ Random Loss of Variation ........................................................................................ The Potential for Natural Selection .......................................................................... TOWARD AN IMPROVED MODEL FOR TRIBAL POPULATIONS ................ EPILOGUE .......................................................... ..........................................................
367 368 371 371 371 376 378 379 382 382 388 390 394 396
400
401 403 407
'The original research on which this review is based was supported by the Energy Research and Development Administration (now Department of Energy) and the National Science Foundation.
0066-4197/78/1215-0365$01.00
365
366
NEEL
Those from the Western World who attempt to enter into the domain of primitive2 man seem to respond in either of two ways. To some it is a constantly threatening experience, challenging beliefs and assumptions of ten poorly perceived by their holder, an experience best discreetly aban doned at the earliest opportunity. For others it is a privileged experience, carrying with it deeply felt responsibilities. There is, on the one hand, the
Annu. Rev. Genet. 1978.12:365-413. Downloaded from www.annualreviews.org Access provided by New York University - Bobst Library on 02/08/15. For personal use only.
humanistic responsibility that springs from the realization that one is there as a representative of a culture that throughout the world has ruthlessly violated the rights of primitive man. There is, on the other hand, especially for scholars, the scientific responsibility that follows from the sad but indis putable fact that primitive man will soon be no more. Within the next generation our opportunities will be gone to visit ourselves in a reasonable facsimile of the conditions under which the evolution that renders us dis tinctly human has occurred. How often has that thought, and the doubt that I was making the most appropriate observations possible under the circum stances, kept me awake in my hammock on one of those soft tropical nights that so miraculously follow the heat of the day. This review will deal with the attempts of a multidisciplinary team to characterize in some depth the genetic structure of a particular tribe of South American Indians, the Yanomama. This effort is an aspect of a larger program which has thus far resulted in contacts with some With respect to the Yanomama, our field work began in
15 Indian tribes. 1 964, when Dr.
Napoleon Chagnon initiated his anthropological studies. This was followed by a series of 9 eXpeditions to the tribe, the first in
1966,
d
each expedition
0, > 1 00, >400, > 1000 ) at various generations following its appearance, for various values of m. (An m value greater than 1 .0 can be due either to positive selection for an allele or to a generally expanding population in which the allele increases at the same rate as the type allele.) Section A of the table illustrates expectation if the
399
Annu. Rev. Genet. 1978.12:365-413. Downloaded from www.annualreviews.org Access provided by New York University - Bobst Library on 02/08/15. For personal use only.
YANOMAMA POPULATION STRUCTURE
census was from newborn-to-newborn, Section B if from adult-to-adult. In view of the high infant mortality in such populations, the infant-to-infant census is rarely feasible and one will usually base any treatment on the adult generation. The predictions of Table 4 have been checked through 1 6 generations by the above-described computer simulation with very satisfac tory agreement. Thompson & Neel (106) have also considered the conse quences of fluctuating values of m. In most Indian tribes, numbering no more than 2000 adults (aged 1 5-40), 100 copies of an allele would constitute a genetic polymorphism. Table 4 illustrates the great importance of relatively small differences in m to the probability of such a polymorphism. Thus, selecting from the examples of Table 4, the probability of an allele being represented by 100 or more copies Table 4
The probability o f a rare variant exceeding a specified number of copies (0, 1 00,
4 00 , 1 000) at t he given generation (t) wi th various schedules of variant increase p er gen eration (m), in a population with the structure of the Yanomamaa Number of copies >0
> 1 00
A . Simulation m = 0 .98
m = 1 .0
m = 1 .05
m
=
l .l
> 400 c
0 .0242
1 00
4 00
0 . 00 1 3 5 0.0 1 4
16
0 .0296
1 00
0.0049
400
0 .00 1 2
2 0.0 1 5 2 0 .0 3 0 2 0.0 1 1
m
=
=
1 .05
1 .1
a part A of the
7 0.0 1 9 4 0.0 1 1 7 0.0 20 6 0.0 1 8 3 0.0 69 0.0 37 5
0.0
16 8
13
0.0 8 0 0.0 1 0 3 2 0.0
14 4
27
0 . 0 38
0.0 3 3 6
16
0.044 1
0.0 1 3
0 .0 1 0 6 1
1 00
0 .0246
0 .024 1
0.0228
0.0204
400
0 . 0 244
0.0244
0 . 06 1 5
0 .0 1 60
0.0244 0.0 3 2 8
0.0244
16 1 00
0 .048 7
0 .048 7
0.04 8 7
0.0486
400
0.0487
0 .048 7
0.048 7
0.0487
4 0.0 1 1
16
0 .0 8 5 7
1 00
0 .0 1 4 8 0 .0 0 3 7
0 .0 2 3 3 2 0.0 26
4
c =
0.078 7
0 .40 16 0.0 23 4 0.0 38
0.0
8 0.0 5 1 4 0.0 8 8
16
0 . 1 302
3 0 . 0 28
0 .0 3 8 4 11 0.0 27
1 00
0 .0 7 5 5
0.07 1 3
0.0600
0.0425
400
0.07 5 0
16
0 . 1 840
0 . 07 5 0 2 0.0 3 1
0.0750 7 0.0 1 5
0.0750 18 0.0 32
1 00
0 . 1 5 00
0 . 1 498
0 . 1 494
0 . 1 484
400
0 . 1 5 00
0 . 1 5 00
0 . 1 500
0 . 1 5 00
400 m
0 .67
0 .0 2 5 7
B. Ad u It-to-aduIt m = 1 .0
=
3 0.0 7 2 3 0 .0 39 6 0 .0 4 8
16
> 1 000
0.0
27
26
table pertains to the introduction of the variant into a just-born child, in
which case c, the geometric parameter in the ex pression describing the distribution of family size, has a value of 0 . 6 7 . Part B pertains to the introduction of the variant into the population b y a young adult, in which case c has a value of 0.40.
Annu. Rev. Genet. 1978.12:365-413. Downloaded from www.annualreviews.org Access provided by New York University - Bobst Library on 02/08/15. For personal use only.
400
NEEL
at generation 100 is 0.00039 at m = 0.98, but 0.0241 at m = 1 .05. However, given Amerindian tribal sizes, clearly no tribe has experienced m values of 1 .05 or 1 . 10 for very many generations, and the most appropriate perspec tive on founder effect is supplied by the lower m values. The table also illustrates the high probability of mutant loss within a relatively few genera tions, first emphasized by Fisher (99) with a deterministic model, but also demonstrates that contingent upon survival, an allele after 100 generations will, even for small values of m , have close to a 50% probability of emerging as a private polymorphism. The occurrence of a private polymorphism of serum albumin with an allele frequency of 0.076 in the Yanomama has already been mentioned. We estimate 1066 copies of this allele in the adult generation of Yanomama. From Table 4 we see that for values of m less than 1 .0, such a founder effect should be very rare, but for an expanding tribe, relatively much more common. The treatment of Section B of Table 4 is obviously also appropri ate to the introduction of a single unique allele into a tribe by an immigrant.
R andom Loss 0/ Variation The subject of random loss of variation, to which in effect the preceding section was directed, can also be approached in a highly empirical fashion from data on multiallelic systems in the Yanomama. In addition to the various typings already mentioned, the frequency of the HLA haplotypes for the A and B loci have been determined for 2 1 8 persons in 8 Yanomama villages, the number examined per village ranging from 1 5 to 74 (107). The villages in question were in the central portion of the tribal distribution, so that recent admixture with representatives of other tribes was most un likely. There were no blanks (designated Xl) with the battery of antisera employed for typing antigens of the A series but 8. 1 % blanks (designated X2) for typings in the B series. The data suggest the presence of 5 alleles at the A locus and at least 6 at the B locus, the uncertainty arising from the ambiguities implicit in the blank phenotype at the B locus. Figure 4 illustrates the range of gene frequencies encountered in these villages for the HL-A alleles as well as the MNSs, Fj', Rh, and Jk
