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Maize diversity and ethnolinguistic diversity
in Chiapas, Mexico
Hugo R. Perales*
†
, Bruce F. Benz
‡
, and Stephen B. Brush
§
*Departamento de Agroecología, El Colegio de la Frontera Sur, Carretera Panamericana y Periferico Sur s兾n, San Cristobal de las Casas, Chiapas, 29290,
Mexico;
‡
Department of Biology, Texas Wesleyan University, Fort Worth, TX 76105; and
§
Department of Human and Community Development,
University of California, Davis, CA 95616
Communicated by B. L. Turner II, Clark University, Worcester, MA, November 24, 2004 (received for review August 22, 2004)
The objective of this study is to investigate whether ethnolinguistic
diversity influences crop diversity. Factors suggest a correlation
between biological diversity of crops and cultural diversity. Al-
though this correlation has been noted, little systematic research
has focused on the role of culture in shaping crop diversity. This
paper reports on research in the Maya highlands (altitude > 1,800
m) of central Chiapas in southern Mexico that examined the
distribution of maize (Zea mays) types among communities of two
groups, the Tzeltal and Tzotzil. The findings suggest that maize
populations are distinct according to ethnolinguistic group. How-
ever, a study of isozymes indicates no clear separation of the
region’s maize into two distinct populations based on ethnolin-
guistic origin. A reciprocal garden experiment shows that there is
adaptation of maize to its environment but that Tzeltal maize
sometimes out-yields Tzotzil maize in Tzotzil environments. Be-
cause of the proximity of the two groups and selection for yield,
we would expect that the superior maize would dominate both
groups’ maize populations, but we find that such domination is not
the case. The role of ethnolinguistic identity in shaping social
networks and information exchange is discussed in relation to
landrace differentiation.
crop diversity 兩 culture 兩 Maya ethnic groups 兩 cultural diversity
A
correlation between biological diversity and cultural, or
ethnolinguistic, diversity has been noted by ecologists (1),
and crop scientists have likewise posited a relationship between
crop diversity and cultural diversity (2). An association between
crop diversity and cultural diversity is logical for several reasons.
Anthropologists and geographers have noted that cultural
groups often occupy distinct environments (3, 4) and that
cultures are often defined by different production practices, food
habits, and rituals that use crops (5). Moreover, the distinct
knowledge systems and social networks that identify cultures are
likely to influence the flow of seed among farmers, possibly
creating culturally defined agricultural environments that are
akin to other environments occupied and used by humans (6).
However, most research on crop diversity (7) has focused on
environmental adaptation and gene flow as the principal vari-
ables in explaining crop diversity, and the contribution that
cultural diversity might make to generating and maintaining crop
diversity has received little attention.
Maize Diversity in Mexico
Mesoamerica is a ‘‘megacenter’’ of biological diversity and one
of the world’s most culturally diverse regions, with ⬎200 lan-
guage groups. The region is also a center of domestication, crop
evolution, and diversity both among and within crop species (8).
Maize is Mesoamerica’s premier crop, and maize diversity is
greater in Mesoamerica than anywhere else. Edgar Anderson, a
pioneer in the field study of Mesoamerican maize, observed long
ago (9) that ‘‘maize is a sensitive mirror of the people who grow
it,’’ but no systematic relationship has been established between
cultural diversity and biological diversity of maize in Me-
soamerica. A cultural basis for biological diversity in maize is
likely because of the central role played by conscious selection
and exchange. Nevertheless, this cultural basis is obscured by
natural selection (environmental adaptation), migration, and
economic factors such as markets.
Comparison of case studies on Mexican maize agriculture
reveals several common management features:
Y
Persistence of local maize types.
Y
Relative dominance of one or two types at both the household
and community levels.
Y
Cultivation of minor varieties, which contribute minimally to
overall production.
Y
High substitutability of different maize types for tortillas, the
basic staple.
Y
Selection of seed from harvested ears, apparently based on an
ideotype of local maize.
Y
Small but consistent acquisition of new seed from neighbors
and more distant sources.
In sum, research on the maize systems of Mexico has shown
them to be open but conservative in terms of seed management
and farmer selection.
Race is the fundamental building block of conventional crop
population biology of maize, as well as farmer management and
crop improvement programs (10). The crop is conventionally
divided into regional populations or races that are distinguish-
able by morphological, biochemical, and genetic markers (11).
Continuous variation occurs among maize races in Mexico,
although regional clusters or complexes are also apparent, each
comprising several races that are more closely allied with one
another and genetically more distant from races in other clusters.
Ethnobiological research has shown that Mesoamerican farmers
recognize and maintain several races within a single cropping
system in response to microenvironmental and market factors
(12, 13). Environment plays a well documented role in the
regional distribution of maize types (14), but other possible
factors have received only minor attention. In this article, we use
the term ‘‘landrace’’ to refer to a population that is distinguished
by farmers and oftentimes generically referred to as ‘‘cr iollo,’’
meaning ‘‘local’’ maize. Farmers in Mexico recognize variation
within landraces primarily by grain color, although other char-
acters are sometimes taken into account. Here, we use the term
‘‘variety’’ to refer to variants of landraces that are named by
farmers.
Consideration of the aforementioned research suggests four
reasons for the likelihood that factors other than environment
contribute to maize diversity. First, the ecogeographic analysis of
maize races by Sanchez and Goodman (14) indicates that several
races coexist as groups in a small number of genotype-by-
environment (g ⫻ e) interaction zones. The higher elevations
(⬎1,800 m) of the state of Chiapas constitute one broad g ⫻ e
zone with Oloto´n and Comiteco as the two dominant races.
†
To whom correspondence should be addressed. E-mail: hperales@sclc.ecosur.mx.
© 2005 by The National Academy of Sciences of the USA
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Second, a small but regular exchange of seed material occurs
beyond community boundaries (15). Third, farm-level research
shows that Mexican farmers seek and test new maize types either
as new varieties or as sources of new traits (16). Finally, there
appears to be a high substitutability of maize types for the
principal uses, such as tortillas and tamales (17). The interaction
of g ⫻ e zones, seed flows, farmer selection, and substitutability
should act to homogenize maize populations within similar
environments, but, in fact, we find diversity of both principal and
specialized (often colored) maize in relatively small regions,
which is the case in highland Chiapas.
Study Site
Research was carried out between September 1999 and Decem-
ber 2002 in the highlands of Chiapas, Mexico, in municipalities
surrounding San Cristobal de las Casas. Our study focused on
maize populations and farmer knowledge in Tzotzil and Tzeltal
communities in the municipalities of Chamula and Oxchuc at an
altitude ⬎1,800 m (Table 1 and Fig. 1). The Tzeltal and Tzotzil
are widespread in Chiapas and extend into different altitude
zones. Chamula and Oxchuc municipalities were chosen to
minimize environmental differences between the farming areas
of the ethnolinguistic groups under study. The climate of both
municipalities is temperate, with rainfall concentrated in the
summer and fall and averaging 1,000–1,200 mm per year. The
region’s eastern side, occupied by the Tzeltal, is slightly wetter.
Neither the Tzotzils nor the Tzeltals have a centralized political
unit; rather, they are loosely organized by community and
municipality. Chamula has 107 predominately Tzotzil-speaking
communities, and Oxchuc has 82 predominately Tzeltal-
speaking communities.
Chiapan maize constitutes a distinct regional cluster, with
seven races characterized by late maturity, tall plants, 23–28
leaves per plant, many tassel branches, long ears, and extreme
sensitivity to photoperiod and temperature (11). Above 1,800 m
of altitude and in the lands of the highland Tzeltal and Tzotzil,
the two most common races are Oloto´n and Comiteco (Fig. 2).
In Mexico, Oloto´n is present only in Chiapas in the highlands.
It is characterized by thick cobs, a bulky base with irregular rows,
and large, rounded, flinty grains. Comiteco probably originated
in Chiapas and is not found elsewhere in Mexico. It is charac-
terized by very long ears (up to 35 cm), among other attributes.
Bretting et al. (18) studied the maize of the nearby highlands of
Guatemala and found that isoenzymatic variation between
Oloto´n and Comiteco cultivated in Guatemala was not signifi-
cant. Oloto´n maize from Mexico appears to be smaller than that
found in Guatemala, whereas the reverse may be true for
Comiteco.
Color is the single most important characteristic in Mayan
farmer nomenclature, classification, and selection of maize (19,
20). Typically, different colors within a community are basically
of the same race. Previous research in the midaltitudes (500–
1,200 m) of Chiapas (17, 21) documented relatively widespread
displacement of local varieties by improved ones, although
landraces were maintained on marginal soils and by households
with poor access to credit, fertilizer, and labor. In contrast, this
study confirms that farmers in the highlands of Chiapas (i.e.,
⬎1,800 m in altitude) are similar to those in other highland
regions in Mexico (13) in maintaining local maize and experi-
encing no major or lasting intrusion of modern varieties.
As shown in Table 2, the inhabitants of both municipalities
practice small-scale, subsistence-oriented farming that is subsi-
dized by off-farm employment and commerce. Land tenure
combines communal ownership with individual use rights. Maize
is the predominate crop throughout the region and is grown
primarily as a subsistence crop. Our household surveys indicated
that a small percentage of the households in Chamula and
Oxchuc sold maize in 2000, whereas a minority of the households
Table 1. Characteristics of communities sampled for maize in the highlands of Chiapas in 2000
Ethnolinguistic
group and
municipality Community
Common
garden
group*
Altitude,
m above
sea level
No. of
households in
community
†
No. of households
sampled for
maize
No. of maize
samples
Average maize
planting,
hectares
Tzotzil of Chamula Los Ranchos I 2,210 71 24 65 1.2
Tentic I 1,980 168 26 56 0.7
El Crucero II 2,470 87 26 52 1.5
Pozuelos II 2,380 79 36 80 0.8
Totals 112 253 1.1
Tzeltal of Oxchuc Pacbilna III 1,860 117 32 78 1.1
El Retiro III 2,150 72 35 59 1.2
Piedra Escrita III 1,880 26 24 45 1.1
Tushaquilja IV 1,880 165 32 59 1.9
Rancho del Cura IV 1,980 137 33 72 1.9
Totals 156 313 1.5
*Common garden groups used for analysis (see Table 4).
†
No. of households in community from Instituto Nacional de Estadı´stica Geografı´a e Informa´ tica (22).
Fig. 1. Tzotzil and Tzeltal communities were studied in two municipalities of
the Maya highlands of Chiapas, Mexico.
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in Chamula and half of those in Oxchuc reported being self-
sufficient in the grain. A small but apparently regular amount of
seed is acquired from off-farm sources in each municipality.
Materials and Methods
Four Tzotzil communities in Chamula and five Tzeltal commu-
nities in Oxchuc were sampled for maize. Households were
randomly selected for sampling and data gathering. In the
Chamula villages, we sampled 112 households, and in Oxchuc we
sampled 156 households. A survey instrument was used to
determine household characteristics, as well as maize names,
characteristics, origin, and management.
Six ears of seed-quality maize were sought for each type sown
by each farm household in the 1999 season. In all, 253 maize
samples were collected in Chamula, and 313 were collected in
Oxchuc. Maize samples (239 for Chamula and 260 for Oxchuc)
were characterized for ear morphology (length, diameter, cob
diameter, and seed length, width, and thickness), and 40 samples
from Chamula and 49 samples from Oxchuc were measured for
cob characteristics (rachis diameter, cupule width, and rachid
length) by using a caliper and a microscope with an ocular
micrometer. Group comparisons were based on averages for
collections within communities.
Allele frequency was determined for eight isozyme loci for
maize landraces pooled within four Tzotzil communities from
Chamula and five Tzeltal communities from Oxchuc. Following
Stuber et al . (23), Acp, Est, Idh1, Idh2, Me, Pgd1, Pgd2, and Phi
were determined for 73 seeds from Chamula and 64 seeds from
Oxchuc. Modern varieties Mo17, Tx303, and B73 were used as
controls in each gel. Data were analyzed with Tools for Popu-
lation Genetic Analysis (
TFPGA) software. Among-population
genetic structure was analyzed by hierarchical F statistics ac-
cording to Weir (24). Nei’s genetic distance (25) between
communities was calculated, and an unweighted pair group
method with arithmetic means dendogram was produced.
Reciprocal common gardens of maize landraces were planted
in two communities in each municipality in 2001. The gardens’
purpose was to provide data on local adaptation of the maize
populations from the two municipalities. Thirteen maize vari-
eties from the four communities of Chamula and 12 varieties
from the five communities in Oxchuc were planted in a ran-
domized complete block design with three replicates; landraces
of the different colors were included for both municipalities. The
plots were rented from local farmers and managed according to
local practices but with more consistent fertilizer application
(120:46 N:P
2
O
5
). The garden blocks comprised 5 ⫻ 5 m plots
with three plants in 1 ⫻ 1 m hills, and data were taken from the
central 3 ⫻ 3 m section of each garden block. Some experimental
plots were lost, but in all cases at least two replicates per variety
were included. Data were analyzed as a factorial experiment for
each community (origin of seed ⫻ color) with
SAS statistical
analysis software general linear model procedures. Analysis of
yield data showed no significant differences by color (for exam-
ple, F ⫽ 1.96, P ⫽ 0.1966 for Los Ranchos and F ⫽ 0.37, P ⫽
0.8278 for Piedra Escrita), so the garden data are presented by
community and ethnic group irrespective of color.
Results
Survey information determined that 95% of the seed lots planted
in the 1999 season originated in the community examined. A
Fig. 2. The two most common maize races of the Maya highlands are Oloto´n(Left) and Comiteco (Right).
Table 2. Household characteristics by community
Characteristic*
Tzotzil of
Chamula
Tzeltal of
Oxchuc
Tzotzil speaking, % 99.04 4.17
Tzeltal speaking, % 0.96 94.37
Spanish speaking, % 65.93 81.91
Income from commerce, % 20.13 6.46
Family members migrated for
work, %
10.64 21.11
Planted maize in 1998, % 100 100
Sold maize last year, % 11.41 11.97
Maize harvest sufficient for
household needs, %
35.85 50.17
Number maize types兾household
(mean, SD)
2.2 (0.2) 1.9 (0.2)
No. of years with seed lot
(mean, SD)
30.6 (5.9) 27.2 (4.5)
Original seed lot from
community, %
96.7 93.2
Origin of seed lot from
parents, %
86.6 83.7
Yield of maize reported,
kg兾hectares (mean, SD)
936.6 (189.0) 589.7 (200.8)
*Percentages are for households unless otherwise noted. Source for language
is ref. 22; otherwise, information is from field data.
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small (⬇5%) but consistent proportion of introduced seeds lots
was recorded in all communities. All five recognized colors were
present in all communities. On average, Tzotzil and Tzeltal
communities had 2.2 and 1.9 varieties per household, respec-
tively. White and yellow maize types were equally common in the
Tzotzil communities, but yellow types accounted for two-thirds
of the maize area in Tzeltal communities. In Chamula, 20% of
the households had red maize, in contrast to only 5% in Oxchuc,
perhaps related to the fact that more than twice as many Tzotzil
informants reported using red maize for medicinal purposes than
did Tzeltal informants.
Maize collected in Tzotzil and Tzeltal communities suggests
two distinct morphotypes that correspond to the Oloto´n and
Comiteco races according to Wellhausen et al. (10). Statistical
differences for morphological characters (e.g., row number, ear
length, ear diameter, and grain thickness) distinguish the types
from each community (data not reported).
Significant phenological, morphological, and yield differences
were observed when landraces from both Tzotzil and Tzeltal
communities were planted in reciprocal gardens (Tables 3 and 4).
Varieties yielding poorly in one environment had much larger
differences between tassel and ear onset than the same landraces
in an environment to which they were better adapted. For example,
Pozuelos (Tzoltzil) landraces planted in Rancho del Cura (Tzeltal)
had a difference of 24.9 days, whereas in Pozuelos, the same
landraces had only 10.7 days’ difference (data not shown). When all
landraces were analyzed by origin of the seed (Tzotzil vs. Tzeltal),
we found that Tzotzil landraces were poorly adapted to the Tzeltal
environments. In the Tzotzil environments, however, Tzeltal land-
races showed contrasting results. When communities near the
Table 3. Phenological and morphological characteristics from reciprocal garden experiment for
Tzotzil and Tzeltal gardens
Characteristic
Tzotzil gardens Tzeltal gardens
Seed origin
F
Seed origin
FTzotzil Tzeltal Tzotzil Tzeltal
n 71 61 76 71
No. of days to tassel 123.14 139.53 21.10*** 110.36 119.72 47.77***
No. of days to silk 136.21 149.10 13.62*** 127.03 131.82 4.97*
Plant height, cm 292.54 312.46 7.82 ns 280.90 303.75 6.72*
Ear height, cm 149.00 163.36 6.09* 138.55 162.77 4.38*
Length of tassel, cm 48.13 47.72 0.67 ns 46.11 46.78 1.63 ns
No. of tassel branches 15.03 16.93 13.52*** 15.50 16.41 2.12 ns
Length of ear, cm 16.13 18.16 22.08*** 13.77 18.65 68.74***
Width of ear, cm 4.13 4.03 3.44 ns 3.94 4.12 4.42*
Length of grain, mm 10.56 10.62 0.02 ns 9.95 10.56 18.18***
Width of grain, mm 9.73 9.63 0.46 ns 9.66 9.96 5.57*
Thickness of grain, mm 5.91 6.04 2.78 ns 6.27 6.15 1.35 ns
Weight of grain, g 4.28 3.91 7.55** 4.16 4.51 9.36**
Cob width, cm 2.57 2.63 1.54 ns 2.42 2.62 15.74***
Significance level:
*
, 0.05;
**
, 0.01;
***
, 0.001; ns, nonsignificant.
Table 4. Yields (tons兾hectare) of reciprocal gardens for 13 Tzotzil and 12 Tzeltal landraces
Origin of seed*
Garden location
Tzotzil Tzeltal
Los Ranchos
(I)
Pozuelos
(II)
Piedra Escrita
(III)
Rancho del Cura
(IV)
By ethnic group
Tzotzil 3.40 b 2.57 a 2.28 b 0.78 b
Tzeltal 4.05 a 2.01 b 3.95 a 1.52 a
n 35兾33 37兾33 38兾37 38兾34
F ⫽ 8.53 F ⫽ 6.97 F ⫽ 40.45 F ⫽ 23.42
P
F
⫽ 0.0050 P
F
⫽ 0.0105 P
F
⫽ 0.0001 P
F
⫽ 0.0001
By region
Tzotzil
Los Ranchos (I) 3.82 ab 2.19 ab 3.10 b 1.18 a
Pozuelos (II) 3.08 b 2.90 a 1.54 c 0.47 b
Tzeltal
Piedra Escrita (III) 4.01 a 1.96 b 4.04 a 1.44 a
Rancho del Cura (IV) 4.17 a 2.15 ab 3.69 ab 1.75 a
n ⫽ (I兾II兾III兾IV) 15兾20兾25兾817兾20兾24兾918兾20兾28兾917兾21兾25兾9
F ⫽ 5.41 F ⫽ 5.24 F ⫽ 24.64 F ⫽ 15.41
P
F
⫽ 0.0025 P
F
⫽ 0.0030 P
F
⫽ 0.0001 P
F
⫽ 0.0001
*Origin of seed by region includes communities closest to the common garden (see Table 1). ANOVAs for
bifactorial experiment (origin of seed ⫻ color of variety); color of grain was nonsignificant in all cases (data not
reported). Mean differences by Tukey’s test (letters beside yields) are reported by common garden.
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common garden were defined as a single region, a similar pattern
is observed: Tzeltal maize performed better in its own environ-
ments, but Tzotzil maize did not always show clear superiority in its
environments. In the case of Los Ranchos (Tzotzil), local maize did
not out-perform either Tzeltal maize or that of the other Tzotzil
community (Pozuelos). In contrast, in Pozuelos, local maize had
greater yield not only compared with the Tzeltal maize but also
compared with the other Tzotzil landraces from Los Ranchos.
Thus, the common garden experiment suggests that there is a
tendency for the maize populations from the region to be
structured phenologically and morphologically and according to
local adaptation, although adaptation is not clearly indicated
across the entire study area. Only the Tzotzil maize showed clear
adaptation to its own environments, performing poorly in
Tzeltal environments. Tzeltal maize shows local adaptation but
is also competitive in some Tzotzil environments.
Isozyme analysis indicates differences for allele frequencies in
Tzotzil and Tzeltal varieties, although the analysis suggests very
weak differentiation. A deficiency of heterozygotes was found for
the whole sample (F
IT
⫽ 0.4849 and F
IS
⫽ 0.4841), suggesting some
inbreeding (26). F
ST
was very low (0.0019, not significantly different
from 0), suggesting weak differentiation between ethnolinguistic
subpopulations. These results are consistent with Pressoir and
Berthaud’s (27) findings for Bolita landraces from Oaxaca. Overall,
Nei’s genetic distance (25) was very small between Tzotzil and
Tzeltal landraces (⬍0.02, i.e., 0.98 identity). Fig. 3 is an unweighted
pair group method with arithmetic means dendogram based on the
isozyme results, which shows that the maize populations of the two
ethnolinguistic groups do not cluster according to whether the
maize is from one or the other ethnolinguistic group (26).
Discussion
We found morphological and agronomic differences for maize
landraces planted by Tzotzils of Chamula and Tzeltals of Oxchuc.
Reciprocal garden experiments suggest local adaptation for Tzotzil
landraces and wider adaptation for those of the Tzeltal. Isozyme
analysis suggests a small genetic distance, and weak population
differentiation shown by isozyme analysis suggests weak genetic
differentiation. In conventional taxonomy of Mexican maize (10,
11), Tzotzil maize from Chamula is Oloto´n and Tzeltal maize from
Oxchuc is Comiteco. Farmers in the two ethnolinguistically distinct
municipalities maintain maize populations that can be identified
according to traits that are easily recognized by them, especially
grain color, flint vs. dent grain, ear length and weight, and the ratio
of ear diameter to length. These populations are maintained despite
seed movement between the communities, which might otherwise
have pushed them to be less distinct. Indeed, the isozyme results
suggest that variation does not correlate with ethnolinguistic dif-
ferences, although morphological selection may have little effect on
unlinked biochemical traits. These findings are compatible with
those of Pressoir and Berthaud (27, 28) for maize landraces in the
state of Oaxaca. The phenological and agronomic results from
reciprocal gardens indicate that environmental adaptation may
partially account for the maintenance of different populations, but
a strong environmental basis for the differentiation between the
two municipalities is lacking. It is arguable that the maize of Tzeltal
farmers from Oxchuc is equally adapted to some areas in Chamula
as the maize that is selected and maintained there by Tzotzil
farmers. This finding suggests a possible role for ethnolinguistic
diversity as a basis for maize diversity in this region and, more
generally, in the unconscious selection and evolution of domesti-
cated plants (29).
Although our research did not directly address the actual mech-
anisms involved in an association between maize diversity and
ethnolinguistic diversity, two ethnographic observations are rele-
vant. First, there is no strong differentiation between Tzotzil and
Tzeltal people in terms of their use of maize. Our fieldwork found
their cuisines and ritual uses of maize to be similar, and this
similarity is confirmed by other ethnobiologists (19, 20). Second,
farmers here, as elsewhere in Mexico, speak of ‘‘our maize,’’ but
they are interested and eager to try maize from outside their
communities. For instance, when we offered to provide seed of any
maize of our collections to farmers with whom we worked, 94% of
the Tzotzil farmers requested maize from the Tzeltal communities,
and 71% of the Tzeltal farmers requested maize from Tzotzil
communities. Like other maize farmers who have been studied in
Mexico, the Tzotzil and Tzeltal farmers of highland Chiapas use
several criteria in their selection, but yield is always a major
consideration. In this small-scale, subsistence farming economy, the
struggle for self-sufficiency is often unsuccessful, and precious
economic resources are spent on purchasing grain. As a conse-
quence, the judgment of which landrace to plant is critically
important. Because farmers change seed periodically or supple-
ment existing stocks with new seed, it is essential that they trust the
information about the maize they obtain from another source, and
this confidence in the information source might be where ethno-
linguistic differentiation contributes to maize diversity.
Human ecologists (30) define culture as a mechanism that
organizes the flow of information essential for survival. Cultures
develop traditional knowledge based on experience and adaptation
to a local environment. Traditional knowledge is commonly well
developed for genetic resources because of their paramount im-
portance for the survival of communities practicing subsistence
agriculture. The transmission of this knowledge is biased by lan-
guage and local cultural differences; an example of this bias is
individuals conforming to local practices because doing so is less
costly than experimenting and learning (30, 31). Atran et al. (6)
report that distinct folk ecological models affecting land use among
the lowland Maya of Guatemala’s Department of El Pete´n are
significantly influenced by ethnic group affiliation and maintained
by cultural segregation. Social networks of the different groups
living in the region did not include people outside of an individual’s
ethnic group. This finding shows that socially acquired information
is strongly bound to the ethnic group. We posit that the morpho-
logical separation between Tzotzil and Tzeltal maize arises when
farmers seek to reduce the costs of obtaining essential information
about a landrace’s performance by seeking it locally from people
who are trusted and in areas where it has been tested in familiar
circumstances. Thus, the cost of information should bias farmers
toward local landraces, thereby helping to segregate crop popula-
tions according to ethnolinguistic group.
We thank Teresa Santiago Vera, Gaspar Sa´ntiz Lo´pez, Angel Martı´nez
Va´zquez, Oliva Ceballos Alpuche, Manuel de Jesus Ruiz Dı´az, and Lucı´a
Bautista Chisna´ for assistance with the fieldwork and Leonardo Toledo
for assistance with Fig. 2. We are grateful to the people of Chamula and
Oxchuc for sharing their time and knowledge. This work was supported
by National Science Foundation Grant SBR-9976892 and a grant from
the Ford Foundation’s Mexico City Office.
Fig. 3. Isozyme analysis shows weak differentiation and a lack of clustering
of maize populations according to ethnolinguistic group.
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SCIENCES
1. Moore, J. L., Manne, L., Brooks, T., Burgess, N. D., Davies, R., Rahbek, C.,
Williams, P. & Balmford, A. (2002) Proc. R. Soc. London Ser. B 269, 1645–1653.
2. de Candolle, A. (1885) Origin of Cultivated Plants (D. Appleton, New York).
3. Kroeber, A. L. (1939) Cultural and Natural Areas of Native North America
(Univ. of California Press, Berkeley).
4. Nettle, D. (1999) Linguistic Diversity (Oxford Univ. Press, Oxford).
5. Brush, S. B. (2004) Farmers’ Bounty: Locating Crop Diversity in the Contem-
porary World (Yale Univ. Press, New Haven, CT).
6. Atran, S. Medin, D., Ross, N., Lynch, E., Coley, J., Ucan Ek, E. & Vapnarsky,
V. (1999) Proc. Natl. Acad. Sci. USA 96, 7598–7603.
7. Wood, D. & Lenne´, J. (1999) Agrobiodiversity: Characterization, Utilization, and
Management (CABI, Wallingford, U.K.).
8. Benz, B. F. (2001) Proc. Natl. Acad. Sci. 98, 2104–2106.
9. Anderson, E. (1947) Ann. Mo. Bot. Gard. 34, 433–451.
10. Wellhausen, E. J., Roberts, L. M. & Hernandez-Xolocotzi, E. in collaboration
with Mangelsdorf, P. C. (1952) Races of Maize in Me xico (Bussey Institution of
Harvard University, Cambridge, MA).
11. Sanchez G. J. J., Goodman, M. M. & Stuber, C. W. (2000) Econ. Bot . 54, 43–59.
12. Bellon, M. R. (1991) Hum. Ecol . 19, 389–418.
13. Perales, R. H., Brush, S. B. & Qualset, C. O. (2003) Econ. Bot. 57, 7–20.
14. Sanchez, G. J. J & Goodman, M. M. (1992) Econ. Bot. 46, 72–85.
15. Louette, D., Charrier, A. & Berthaud, J. (1997) Econ. Bot. 51, 20–38.
16. Perales, R. H., Brush, S. B. & Qualset, C. O. (2003) Econ. Bot. 57, 21–34.
17. Bellon, M. R. & Brush, S. B. (1994) Econ. Bot. 48, 196–209.
18. Bretting, P. K., Goodman, M. M. & Stuber, C. W. (1990) Am. J. Bot. 77,
211–225.
19. Breedlove, D.E&Laughlin, R. M. (1993) The Flowering of Man: A Tzotzil
Botany of Zinacanta´n (Smithsonian Institution, Washington, DC), Vol. 1.
20. Berlin, B., Breedlove, D. E. & Raven, P. H. (1974) Principles of Tzeltal Plant
Classification: An Introduction to the Botanical Ethnog raphy of a Mayan-
Speaking People of Highland Chiapas (Academic, London).
21. Bellon, M. R. & Taylor, J. E. (1993) Econ. Dev. Cult. Change 41, 763–786.
22. Instituto Nacional de Estadı´stica Geografı´a e Informa´tica (INEGI) (1991)
Chiapas, Final Results, Basic Tabulations, XI General Census of Population and
Housing, Vol. 1 and 2 (INEGI, Aguascalientes, Mexico).
23. Stuber, C. W., Wendle, J. F., Goodman, M. M. & Smith, J. S. C. (1988) Tech.
Bull. NC Ag ric. Res. Ser vice 286, 1–87.
24. Weir, B. S. (1996) Genetic Data Analysis II (Sinauer, Sunderland, MA).
25. Nei, M. (1978) Genetics 89, 583–590.
26. Ceballos, A. O. (2003) M.Sc. thesis (El Colegio de la Frontera Sur, San
Cristo´bal, Chiapas, Mexico).
27. Pressoir, G. & Berthaud, J. (2004) Heredity 92, 88–94.
28. Pressoir, G. & Berthaud, J. (2004) Heredity 92, 95–101.
29. Zohary, D. (2004) Econ. Bot. 58, 5–10.
30. Boyd, R. & Richerson, P. J. (1985) Culture and the Evolutionary Process (Univ.
of Chicago Press, Chicago).
31. Soltis, J., Boyd, R. & Richerson, P. J. (1995) Curr. Anthropol. 36, 473–494.
954
兩
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