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Illness, Injury, and Disability Among Shiwiar

Illness, Injury, and Disability Among Shiwiar
Implications of Health-Risk Buffering for the
Evolution of Human Life History
Lawrence S. Sugiyama*
Department of Anthropology and Institute of Cognitive and Decision Sciences, University of Oregon,
Eugene, Oregon 97403
KEY WORDS healthcare; risk; pathology; human life history; evolution; mortality; Shiwiar
ABSTRACT Human life history is distinguished by
long lifespan, delayed reproduction, intergenerational
asymmetric benefit transfers from adults to juveniles and
between adults, and a large brain able to engage in unprecedented
levels of learning, reasoning, and insight. The
evolution of these traits depends on relatively low human
mortality. Understanding why humans have low mortality
is therefore critical for understanding the evolution of
key human traits. One explanation is that the evolution of
food provisioning during periods of health crisis reduced
mortality. This hypothesis turns on health risk having
posed a significant adaptive problem that could be effectively
buffered by healthcare provisioning. Unfortunately,
the frequency, duration, and fitness effects of temporary
disability are difficult to estimate based on osteological
evidence alone, and systematic ethno-biological research
on these issues among extant small-scale societies with
little access to Western medical care is lacking. Here I
present data on 678 injuries and illnesses suffered by 40
Shiwiar forager-horticulturalists, based on physical evidence
and informant reports. A subsample of 17 individuals
provided data on incidence and duration of disability
for 215 pathological incidents. Results indicate that injury
and illness occur frequently across the lifespan. Most living
individuals have suffered temporarily disabling health
crises likely to have been lethal without provisioning. The
fitness effects of surviving these episodes are high, suggesting
that the Shiwiar population structure and lifeway
are dependent on infrequent extended provisioning to
temporarily disabled individuals, and that provisioning of
aid during healthcare crises effectively lowers mortality in
this small-scale society. Am J Phys Anthropol 123:
371–389, 2004. © 2004 Wiley-Liss, Inc.
Life-history theory examines how natural selection
produced age-related allocation of resources between
somatic (growth and maintenance) and reproductive
(fertility, mating, and parenting) effort (e.g.,
Charnov, 1993; Charnov and Schaffer, 1973;
Hawkes et al., 1997; Hill and Hurtado, 1996; Hill
and Kaplan, 1999; Kaplan et al., 2000; MacArthur
and Wilson, 1967; Schaffer, 1974; Williams, 1966).
Four distinctive features of human life-history traits
are long lifespan, delayed reproduction, intergenerational
and asymmetric benefit transfers from adults
to juveniles and between adults, and a large brain
able to engage in unprecedented levels of learning,
reasoning, and insight (e.g., Bryne, 1997; Geary and
Flinn, 2001; Hawkes et al., 1998, 2000; Hewlett,
1992; Hill, 2002; Hill et al., 2001; Hill and Hurtado,
1996; Hill and Kaplan, 1999; Kaplan et al., 2000;
Tooby and DeVore, 1987). The evolution of each of
these features is dependent on humans experiencing
relatively low mortality rates. Understanding why
humans experience low mortality may therefore
“hold the key for understanding a variety of evolved
human features and . . . the evolutionary history of
our species” (Hill and Kaplan, 1999, p. 413).
This study examines health insults and their consequences
among Shiwiar forager-horticulturalists
of Ecuadorian Amazonia to present quantitative
data on health risk among a small-scale population
with little ready access to Western medicine, and to
determine whether the ethno-biological evidence
from this population suggests that care for sick and
injured individuals is likely to be a significant factor
in lowering human mortality under evolutionarily
Grant sponsor: Fulbright Foundation; Grant sponsor: Wenner-Gren
Foundation; Grant sponsor: University of Oregon Office of Research;
Grant sponsor: Center for Evolutionary Psychology; Grant sponsor:
James S. McDonnell Foundation; Grant sponsor: Nathional Science
Foundation; Grant number: BNS9157-449.
Please do not cite without author’s permission.
*Correspondence to: Lawrence S. Sugiyama, Department of Anthropology,
University of Missouri, Columbia, MO 65211-1440.
E-mail: [email protected]
Received 17 June 2002; accepted 31 March 2003.
DOI 10.1002/ajpa.10325
relevant conditions (e.g., Hill and Kaplan, 1999;
Kaplan et al., 2000). Specifically, I present data on
the incidence and cause of 678 injuries and illnesses
suffered by 40 individuals from two communities
(resident populations of 67 and 87, respectively),
based on physical evidence and reported occurrence
of pathologies. A subsample of 17 individuals provided
data on the incidence and duration of disability
for 215 cases. Together, these are used to determine:
1) what health insults this population suffers;
2) with what frequency they occur; 3) with what
frequency and duration they cause disability severe
enough to interfere with subsistence activities and
necessitate survival assistance over the course of the
lifespan; 4) an indication of the fitness effects of
individuals having received long-term aid without
which they are likely to have died; 5) an indication of
whether healthcare provisioning is likely to be a
significant cause of mortality reduction; and 6) the
possible intensity of selection pressure from health
risk in a society with limited access to Western
Humans exhibit a longer juvenile period (the period
between weaning and first reproduction; Pagel
and Harvey, 1993) than other primates, including
other hominoids (e.g., Hawkes et al., 1998; Hill et
al., 2001; Hill and Kaplan, 1999; Kaplan et al., 2000;
Pereira, 1993; Pagel and Harvey, 1993). For instance,
female chimpanzees begin reproduction at
about age 13–15 years (Boesch and Boesch, 2000;
Nishida et al., 1990; Pusey, 1990), whereas in foraging
societies, human females begin reproduction at
about 17–20 years (Hawkes et al., 1998; Hill and
Hurtado, 1996; Kaplan et al., 2000). The evolution of
delayed maturity calls for explanation because, all
else being equal, it increases the probability of death
prior to reproduction, thus causing an average decrease
in age-specific reproductive value (e.g.,
Kaplan et al., 2000; Pagel and Harvey, 1993; Pereira
and Fairbanks, 1993; Williams, 1966).
Humans also have a longer lifespan than their
closest living relatives. For instance, while only
about 9% of wild chimpanzees live to age 50 years,
42% of Ache foragers reached 50 prior to contact
with outsiders (Hill et al., 2001). Chimps senesce
about 20 years earlier than humans, indicating that
the differences in average lifespan are due to long
histories of selection as well as to higher observed
rates of extrinsic mortality (Hill et al., 2001). Evolution
of long lifespan calls for explanation because,
all else being equal, selection operates more strongly
earlier in life when the reproductive payoff of each
additional year of survival is higher than at the end
of the lifespan (Fisher, 1958; Hamilton, 1966; Medawar,
1952; Williams, 1957).
In addition, human forager life is marked by high
degrees of inter- and intragenerational support and
cooperation. Postreproductive aged females support
the reproduction of younger women and their offspring
(e.g., Hawkes et al., 1997, 1998, 2000), and
males contribute resources to mates, other adults,
and juveniles (Hawkes et al., 2001; Hewlett, 1992;
Hill and Hurtado, 1996; Kaplan et al., 2000; Marlowe,
1999, 2001; Winterhalder, 1996). Humans also
exhibit exceptional intelligence, complex social
skills, and a large capacity for developmental learning
(e.g., Byrne, 1997; Bogin, 1999; Geary and Flinn,
2001; Hill and Kaplan, 1999; Kaplan et al., 2000;
Tooby and DeVore, 1987). Kaplan et al. (2000) and
others argued that human adult foraging competence
requires long periods of skill or knowledge
acquisition (e.g., Bock, 2002; Hill and Kaplan, 1999;
Kaplan et al., 2000; Walker et al., 2001). Although
this claim is currently debated and the degree to
which juvenile foragers contribute to their own subsistence
varies (e.g., Bird and Bird, 2002a,b; Blurton-
Jones and Marlowe, 2002), humans are nevertheless
distinguished by a long period of juvenile
dependence (e.g., Bird and Bird, 2002b; Blurton
Jones et al., 1994; Bogin, 1999; Hawkes et al., 2001;
Hewlett, 1992; Hill and Kaplan, 1999; Kaplan et al.,
2000). Lengthy juvenile dependence entails an increased
vulnerability to loss of parental investment
(e.g., Chagnon, 1992; Hagen et al., 2001; Hill and
Hurtado, 1996). Again, evolution of these traits calls
for explanation because, all else being equal, they
decrease the probability that a juvenile will reach
reproductive age.
Mortality reduction allows evolution of delayed
maturation and long lifespan
Three basic factors are used to explain delayed
maturity and long lifespan: demographic factors,
skill and/or knowledge acquisition, and invariant
patterns of allometric growth (Pagel and Harvey,
1993). The demographic perspective emphasizes
that reproductive age and lifespan are largely the
function of extrinsic mortality rates. Species with
high juvenile mortality tend to be faster maturing,
smaller, and shorter-lived, because they cannot afford
the mortality risk of not reaching maturity (e.g.,
Horn, 1978; Rose, 1983; Williams, 1957). Species
with lower juvenile mortality have later maturation,
and can therefore grow larger. Delayed maturity can
evolve when the increased risk of prereproductive
mortality it entails is offset by the acquisition of
fitness-enhancing benefits during the juvenile period.
Thus, long juvenile lifespan is seen as a time in
which a second factor comes into play, the acquisition
of knowledge or skills (e.g., social, parental,
aggressive, or foraging) that either enhance later
fertility and/or reduce later mortality (Bogin, 1999;
Geary and Flinn, 2001; Harvey and Zammuto, 1985;
Hill and Hurtado, 1996; Hill and Kaplan, 1999;
Kaplan et al., 2000; Pagel and Harvey, 1993; Pereira
and Altman, 1985; Pereira and Fairbanks, 1993;
Promislow and Harvey, 1990). For this life-history
pattern to evolve, the acquisition of skills and/or
knowledge that yield fitness payoffs during the adult
lifespan must offset increases in prereproductive
mortality risk. Longer adult lifespan allows more
time for these payoffs to be realized. Therefore,
adult mortality rates covary with age at maturity
and fecundity, such that investments in the juvenile
period are compensated for by higher lifetime fitness.
Decreased adult mortality is expected to allow
increased age at maturity, a longer period of skill or
knowledge acquisition, and longer lifespan (Hill and
Kaplan, 1999; Kaplan et al., 2000; Pereira, 1993).
The third factor in explanations of long lifespan
and delayed maturity focuses on invariant patterns
of allometric growth: the larger an animal’s mature
size, the greater its ability to produce energy, but
the later the animal will begin reproduction because
it takes longer to grow to adult size (e.g., Bonner,
1965; Charnov, 1993; Charnov and Berrigan, 1993;
Lindstedt and Swain, 1988). This approach assumes
a tradeoff between time spent growing and time
spent reproducing. Within a lifespan, the longer it
takes to reach reproductive age, the shorter the period
in which reproduction can take place (Charnov,
1993). The relative time devoted to each is an invariant
function. What varies is the length of lifespan
and the probability of reaching reproductive age,
both of which are set by levels of extrinsic mortality.
According to this view, human maturational timing
fits the pattern expected, based on the length of the
human lifespan (e.g., Alvarez, 2000; Hawkes et al.,
1998), and therefore evolution of delayed maturation
requires “no special explanation” (Blurton
Jones and Marlowe, 2002, p. 201). It is a byproduct
of long lifespan. However, invariant patterns of
growth do not account for all of the variance in
life-history traits across primates (e.g., Harvey and
Clutton-Brock, 1985; Harvey and Zammuto, 1985;
Lindstedt and Swain, 1988; Pereira, 1993; Watts
and Pusey, 1993); an explanation of long human
lifespan is still required.
The “grandmother hypothesis” (Hawkes et al.,
1998, 2000, 2001; Williams, 1957) claims that long
human lifespan is the result of selection favoring the
provisioning of benefits by senior women to descendent
generations. Hawkes et al. (1998) argued that
as humans entered a feeding niche based on difficult-
to-acquire foods (e.g., hard-to-extract tubers
and nuts), juveniles could no longer efficiently support
themselves. Mothers then faced the choice of
foraging where weaned offspring could efficiently
forage for themselves (at some foraging cost to the
mother), or foraging for richer, difficult-to-acquire
resources and provisioning their weaned offspring.
Once provisioning evolved, others could enhance
their fitness by provisioning genetically related juveniles.
The long postreproductive lifespan of
women (and with it, long human lifespan) was in
turn selected for because at some point, the fitness
benefits of provisioning grandchildren outweighed
the benefits of continued reproduction (e.g., Hawkes
et al., 1998, 2000, 2001; Williams, 1957). Selection
for the grandmother effect requires that women
lived long enough to realize the benefits of provisioning
grandchildren; therefore, relatively low mortality
across the lifespan forms one basis for the evolution
of grandmothering (e.g., Hawkes et al., 1998;
Kaplan et al., 2000).
Kaplan et al. (2000) integrate insights from the
demographic, grandmothering, and skill-acquisition
perspectives. They propose that our extended
juvenile dependency and long lifespan coevolved
with 1) the dietary transition to high-quality, difficult-
to-acquire foods (in this case, game animals),
2) an increased investment in learning complex
subsistence strategies to exploit such foods, 3)
increased food sharing and provisioning of conspecifics,
and 4) healthcare altruism, resulting in
lower mortality. In this view, as hominid dietary
reliance on high-quality, difficult-to-acquire game
resources increased, fitness benefits were realized
from a longer prereproductive period of foraging
skill and/or knowledge acquisition. This led to the
coevolution of an increased flow of resources from
older individuals to juveniles in order to support
this period of learning. The increased mortality
risk of a longer juvenile period and lifespan was
countered by the coevolution of mortality reduction
via provisioning to sick and injured individuals
(Kaplan et al., 2000).
A central feature of these models is that lower
extrinsic mortality increases the likelihood that
hypothesized benefits from the evolution of delayed
maturity, long lifespan, exceptional intelligence
and learning capability, and/or intra- and
intergenerational resource transfers can be realized
(e.g., Alvarez, 2000; Blurton Jones and Marlowe,
2002; Charnov, 1991, 1993; Hill and Hurtado,
1996; Hill and Kaplan, 1999; Janson and
Von Shaik, 1993; Kaplan et al., 2000; Pagel and
Harvey, 1993). Understanding why humans experience
relatively low mortality is therefore central
for understanding human evolution and an important
set of basic evolved human traits (Hill and
Kaplan, 1999). Possible explanations include decreased
extrinsic mortality stemming from 1) a
reduction in predation among our hominid ancestors
via increasingly effective use of weapons
and/or coalitional defensive tactics (Hill and
Kaplan, 1999), 2) slow growth and adult protection
that insulates juveniles from foraging competition,
3) slow growth and adult protection that
insulates juveniles from potentially lethal mating
competition with adults (e.g., Bogin, 1999; Janson
and van Shaik, 1993), 4) increased investment in
immune function, and pathogen and parasite resistance
(Aiello and Wheeler, 1995; Hill and
Kaplan, 1999), and/or 5) care and provisioning for
sick and injured individuals (Dettwyler, 1991;
Gurven et al., 2000; Hill and Kaplan, 1999;
Kaplan et al., 2000; Sugiyama and Chacon, 2000).
Here I present ethno-biological data addressing
the latter explanation.
Role of ethno-bioarchaeological evidence for
investigating mortality reduction via
healthcare provisioning
Obviously, health risk is not an evolutionarily
novel problem, and bio-archaeological evidence of
illness and injury is seen among prehistoric Homo
sapiens populations (e.g., Alejandro, 1990; Aufderheide
and Rodriguez-Martin, 1998; Berger and
Trinkaus, 1995; Bush and Zvelebil, 1991; Grauer
and Stuart-Macadam, 1998; Lambert, 1993; Martin
and Frayer, 1997; Owsley and Jantz, 1994; Rothschild
and Martin, 1993; Steckel et al., 2002;
Trinkaus, 1983; Walker, 1989; Webb, 1995). Paleoanthropological
studies can give an indication of the
selection pressure from health risk, and whether or
not individuals may have survived health insults
that would have temporarily interfered with foraging
(e.g., Berger and Trinkaus, 1995; Dettwyler,
1993; Trinkaus, 1983). They are limited in that not
all health insults leave osteological signatures, either
because the insult affected only soft tissue or
because no healing occurred (e.g., when the condition
was lethal). While chronic conditions are likely
to be well-represented because of their observable
effects on skeletons, acute infectious diseases, for
instance, are likely to be underrepresented (Steckel
et al., 2002). The paleo-pathological evidence thus
presents a potentially biased view of pathology prevalence
within a population, particularly among
those showing little evidence of pathology (e.g.,
Wood et al., 1992). This “osteological paradox”
means that we may find fewer observable signs of
pathology in populations suffering high mortality
than in those with higher survival rates, at least in
cases of rapid changes in health status (e.g., Steckel
et al., 2002). Other biases arise because of differences
in preservation according to age and sex, with
older, very young, and female individuals likely to be
underrepresented (Hoppa, 2002).
Further, it is difficult to assess the effects of
health insults on behavior simply from osteological
or dental evidence. For instance, osteological evidence
of degenerative joint disease is not clearly
related to whether or not the individual experiences
disability (Steckel et al., 2002). The duration of disability
(if any) is also difficult to estimate based on
osteological evidence alone. People engage in arduous
work while suffering from injuries that would
appear debilitating in the fossil record (e.g., deformed
foot, severe arthritis, loss of limbs; Sugiyama,
1996; Sugiyama and Chacon, 2000), and we
do not know the relative frequency with which
health insults leaving only soft-tissue (i.e., osteologically
invisible) damage occurred in prehistoric populations,
the probability that these would cause disability,
or the duration of disabilities that did occur.
Without this information, it is difficult to know
whether or not an individual required provisioning
to survive a given health insult.
Ethno-bioarchaeological data from small-scale
egalitarian societies have proven useful for testing
assumptions about the meaning of bio-archaeological
data for understanding behavior and for providing
insight into problems that are paleo-anthropologically
intractable (e.g., Lukacs and Pastor, 1988;
Walker and Hewlett, 1990; Walker et al., 1998).
Suggestive evidence does indicate that health insults
severe enough to prevent food acquisition occur
in present foraging and forager/horticulturalist populations
(Bailey, 1991; Gurven et al., 2000; Sugiyama
and Chacon, 2000), and that individuals may
survive these periods only via relatively costly provisioning
by others (e.g., Gurven et al., 2000; Sugiyama
and Chacon, 2000). Yet little is known about
the frequency and duration of disabling illness and
injury among forager and forager-horticulturalist
populations who live without consistent access to
Western medical attention (but see Bailey, 1991;
Baksh and Johnson, 1990; Chagnon, 1975, 1979,
1992; Gurven et al., 2000; Hill and Hurtado, 1996;
Kaplan et al., 2000; Sugiyama and Chacon, 2000;
Truswell and Hansen, 1976). We do not know how
many individuals suffer such events, how they are
caused, how long they last, how often they occur
across the lifespan, what the effects of surviving
these adaptive bottlenecks might have on individual
fitness, or the probable effects of care and provisioning
on the survival of sick and/or injured individuals
(Hill and Kaplan, 1999). Without such data, it is
difficult to assess the probable effects of healthcare
provisioning on mortality or the probable strength of
selection pressure for the evolution of healthcare
provisioning. What follows is intended to provide
this kind of detailed data for one particular smallscale
The Shiwiar are Upper Amazonian, Jivaroanspeaking
people of eastern Ecuador and northeastern
Peru. Approximately 2,000 Shiwiar occupy a
region along the Corrientes River and its tributaries.
Unnavigable rivers have impeded colonial incursion
into Shiwiar territory from the west (Ecuador).
Shiwiar hostility toward outsiders has deterred colonization
dating back at least to the time of the
Incas. Border conflict between Ecuador and Peru
has limited contact between the Ecuadorian Shiwiar
and colonists in the southeast since the 1940s. Prior
to the 1970s, Shiwiar lived in scattered households
linked by marriage ties and the influence of big men
(Descola, 1988). Since seeking missionary contact in
the 1970s, Shiwiar have cleared dirt airstrips
around which houses now form loose clusters. Although
these airstrips provide some access to medical
and other facilities outside of Shiwiar territory
via missionary aircraft, Shiwiar subsistence remains
based on foraging and horticulture, and they
have severed ties with evangelical missionaries.
Shiwiar live in small kin-based communities in
which some foods are shared; they rely on foraging
by hunting and fishing for most of their dietary fat
and protein, and plant products for fruits, starch,
construction, and tool material; they have little easy
access to Western medicine; and they depend on
relatively simple technology for their livelihood. Shiwiar
also grow a wide variety of horticultural products,
the most important being manioc, plantains,
yams, sweet potatoes, and maize. Each female head
of household maintains and harvests 2–4 gardens at
different stages of production. When she is disabled,
her daughters, husband, or close female relatives
take over garden tasks. For example, when one
woman fell victim to an illness from which she eventually
died, two informants reported that they
jointly maintained her gardens for 3 months, but
stopped when they could no longer sustain the work
necessary to do so and adequately maintain their
own gardens as well. Widowers may maintain their
own gardens, but prior to contact, these men would
have been given new wives.
Both blowguns and muzzle-loading shotguns are
used in hunting, although single-shot cartridge
shotguns are increasingly used when cash is available
for shells. Hunting dogs are used to pursue
terrestrial animals such as collared peccary (Tayassu
tajacu), paca (Agouti paca), acouchy (Myoprocta
sp.), and armadillo (Dasypus sp.) (Sugiyama,
1998). Animals such as agouti (Dasyprocta sp.) are
also killed by hand when cornered in a log or burrow.
Additional terrestrial game taken by Shiwiar includes
tapir (Tapirus terrestris) and deer (Mazama
americana), while the mixed strategy of blowgun
and muzzle-loading shotgun use also yields a variety
of primates—primarily woolly (Lagothrix lagothricha),
howler (Alouatta sp.), and capuchin (Cebus sp.)
monkeys—birds, and small game such as squirrels
(Sciurus sp.; Sugiyama, 1998). It also results in low
failure rates and relatively high per-hour hunting
returns (Sugiyama and Chacon, 2000)
Fishing is done with hook and line and fish poisons.
In the rainy season, the bulk of protein comes
from hunting, accompanied by fishing with hook and
line. During the transition to the dry season, fishing
gradually increases as the larger rivers become shallow
and fishing with poison becomes increasingly
efficient (Sugiyama, 1998, 2000). These dry-season
fish poisonings can produce a large quantity of fish
(Sugiyama, 2000), which are preserved by smoking
them over the fire.
Cultural variability in disabling health crises
A discussion of Shiwiar values is necessary to put
this report in perspective. Two concepts are particularly
important here. The first is shiir waras, literally
“good life” or “being.” To live a good life is to
engage in practices expected of one’s age and sex.
For males it includes hunting, fishing, clearing gardens,
hauling large logs for firewood, protecting
one’s family, being good to one’s wife and children,
speaking strongly in favor of one’s interests, avenging
transgressions against one’s interests and those
of one’s kin group, fearlessness, and independence.
For women it means maintaining productive gardens,
harvesting the produce, caring well for one’s
husband and children, preparing and serving food,
keeping a clean house and house clearing, and, as an
index of one’s productivity, growing manioc sufficient
to prepare and serve large quantities of manioc
beer (nihamanch) to family and visitors.
Kakaram is a complex concept referring not only
to how one goes about these activities, but to one’s
personal, spiritual, and/or political power, a power
acquired through and associated with various spiritual
qualities (Mader, 1999, p. 295–403). Kakaram
is used to refer to men who are killers, i.e., men
called upon as something akin to mercenaries in
warfare. However, the term is also applied to individuals
(including women) who speak powerfully to
advance or protect their interests, do not complain
about hardship, and are recognized as extremely
energetic workers in a society which values hard
work. In behavioral terms, they do valued activities
faster, more efficiently, and with greater intensity
than others. In this context, disability (defined here
as a situation that prevents an individual from leaving
bed or home in a way that precludes foraging or
horticultural work) entails a severity of injury or
illness that is stringent by Western middle-class
standards; an illness or injury must be severe to
warrant the preclusion of activities in favor of bed
rest for any significant length of time.
There is a logical connection between these values
and Shiwiar subsistence economy and the traditional
settlement pattern. Low day-to-day foraging
risk and large productive gardens mean that food
transfers between households are not usually critical
for day-to-day subsistence, thus allowing a relatively
high degree of household autonomy and a
scattered, low-density settlement pattern of one or
two nuclear-family household clusters. This in turn
reinforces household autonomy in production and
the values of hard work, individuality, and independence,
while discouraging lapses in productivity.
Nevertheless, food transfers between households do
occur. Manioc beer is served in large quantities to all
household visitors, at cooperative work parties, and
during feasts. Game and fish are supplied to widows,
old people, and one’s core allies based on matrilocal
postmarital residence and cross-cousin preferential
marriage ties. In turn, these patterns increase the
political importance of attending cooperative labor
parties, as a venue for outward display of coalitional
ties. Thus, social aid occurs in a number of domains
including food sharing, cooperative labor, healing,
and warfare. As the data presented below indicate,
prolonged provisioning to temporarily disabled individuals
also regularly occurs.
Data on health insults were gathered from 40
individuals in two communities (resident populations
of 67 and 87, respectively) during separate
field trips by the author in 1994 and 1995. Additional
information was collected from 1993–1998 in
these and two additional villages. Participant observation,
focal person follows, interviews, and records
of injuries and illness were used to provide an ethnographic
context for Shiwiar reactions to injury.
Genealogical and life-history data were gathered in
formal interviews in four Shiwiar and closely related
villages. Age estimates for younger subjects are
based on birth records, which are accurate to the
month and year for approximately the last 25 years.
Beyond this, accuracy varies depending on the life
circumstances of different individuals, whether or
not they ever attended school, or the age at which
they held a job for which official documentation was
necessary. For individuals roughly 30 and older,
ages were cross-checked or determined by calculating
birth date in relation to significant historical
occurrences (e.g., 1942 border conflict with Peru,
first contact with missionaries, or establishment of a
mission) and the known age of other individuals.
The foraging data cited above come from focal-person
follows and departure/return records from two Shiwiar/
Achuar villages recorded between 1993–1998.
Nineteen male and 20 female Shiwiar individuals
ranging in age from 3–50 were examined to document
scars, broken bones, or other observable signs
of past health insults, using a standard examination
technique. Beginning with the right foot, the examination
proceeded up the right leg as far as was
comfortable for the subject, and then down the left
leg. The left and then right arm were examined,
beginning with the fingers of the left hand, followed
by the front and then rear of the torso, the neck,
face, and head. Visible scars and evidence of broken
bones were noted on standardized forms depicting
front- and rear-view line drawings of the human
form, with enlarged views of the hands and feet.
Each health insult recorded was coded as visible,
reported (by the informant), current, or some combination
of these, to specify the evidence upon which
each health-insult record was based. For each health
insult observed, the subject was asked to provide the
cause, activity being engaged in, and age at which
the event occurred. Informants from one of the sample
villages (n 17) were also asked the duration of
disability if applicable, and this information was
cross-checked with other informants. Disability was
defined as a condition causing informants to be confined
to the bed or house and precluding foraging or
horticultural activities, or a condition which caused
them to stop an ongoing subsistence activity and
return home. Many of the short-duration events
were of the latter type. For instance, a scorpion sting
during gardening caused the victim to stop work for
that day and precluded work the next day. A standard
set of questions about past illnesses, injuries,
and treatments received (either from a shaman or
Western medical practitioner) was then administered.
Potential biases in data recording
While every scar on the skin of young individuals
can be recorded, and much about them recalled,
older individuals appear to have been subject to so
many lacerations, abrasions, and infections that
only the most prominent or most recent can be accurately
recorded. Therefore, recorded adult health
insults reflect only the most prominent cases, i.e.,
the most recent and/or most severe. Further, the
methods used were exceedingly time-consuming,
and there may be individual differences in tolerance
for the study, as well as memory effects and reporting
bias. These problems could not be entirely
solved, but their effect (if any) results in underreporting
or missing data for some incidents recorded:
independent means of cross-checking information
were available, such that overestimation or false
reporting were highly likely to be exposed.
Reporting bias was addressed first by using physically
observable evidence as the principal source of
data. Disability duration and reports of pathologies
leaving no visible evidence were cross-checked with
informants who were present at the time of the
incident in question. Informants were often able to
give considerable detail about the injuries or illnesses
of close kin. Informants’ discussions of health
insults, which shaman caused them with what kind
of iwianch (evil spirit), and a host of other details
indicated frequent correspondence between informants,
particularly for major injuries. Informants
sometimes asked others to clarify information about
which they were unclear, suggesting that they expected
others to remember significant health-related
incidents. Conversely, informants had little
interest in most minor injuries, even though they
could often report the cause of the scar in question.
Finally, Shiwiar joked about preventable or foolish
injuries suggesting that, at least for the incidents
reported here, memory bias is not so great as to be
damaging to the general picture that emerges from
data on long-lasting disability. In fact, memory systems
are expected to have evolved to privilege some
information over others, based on the ultimate fitness
effects of doing so. Particularly “foolish” causes
of injury (e.g., swinging a machete around in play
and cutting oneself, jumping off the house floor and
sustaining a fracture) may be well-remembered specifically
because they were clearly preventable. Severe
health insults may be well-remembered because
they can reveal prevention and healing
strategies, as well as critical assessment of social
support (i.e., separating true committed “friends”
from “fair-weather friends”; Tooby and Cosmides,
1996). However, use of physically observable evidence
as the primary data provided an independent
basis for recording patterns of injury, such that potential
effects of informant memory biases were reduced.
Age/sex distribution of sample
Table 1 shows the age/sex distribution of Shiwiar
individuals included in the sample. One of the males
included in the 31–40-year-old cohort was not examined
during the study because he was not present in
the village. However, prior interviews documented
the cause and duration of a case of near-lethal
snakebite. Because prior documentation of all relevant
variables was available for this case, it was
included in the analysis. The Kruskal-Wallis test
shows no significant differences between the ages of
males and females in the sample overall ( 2 28.6,
df 28, P 0.42) or by 10-year age cohorts ( 2
1.514, df 4, P 0.82). Removing the aforementioned
individual from the sample does not significantly
change this result. This allows direct comparison
of frequency, type, and duration of pathological
conditions between males and females.
Overview of pathological conditions
Among the 40 individuals examined, 678 injuries
and illnesses were recorded. As expected, significant
differences were observed in the relative frequencies
with which different types of pathologies were observed.
Overall, the most commonly observed incidents
were lacerations, followed by infections (including
infectious disease), bites and stings,
puncture wounds, abrasions, pain (either chronic or
periodic), broken bones, and burns ( 2 1,861, df
16, P 0.000). Table 2 provides an overview of the
relative frequency of different classes of health insult
by sex of victim.
Sex differences in pathologies suffered
Males generally suffer disproportionately more illness
and injury than females, a fact that has been
attributed both to higher susceptibility to disease
and engagement in more behavioral risk-taking
among males. Among the Shiwiar, males suffered
significantly more pathologies than females (n 430
and 248, respectively; 2 48.855, df 1, P
0.000). This was true for all pathology types with
adequate sample sizes, including lacerations (n
226, 2 21.68, df 1, P 0.000), infections (n
157, 2 6.94, df 1, P 0.008), bites/stings (n
148, 2 13.08, df 1, P 0.000), puncture wounds
(n 40, 2 6.4, df 1, P 0.011), and abrasions
(n 30, 2 6.53, df 1, P 0.011). Males also
suffered more burns than females, though the difference
was not quite statistically significant by conventional
standards (n 13, 2 3.77, df 1, P
0.052). Males and females did not differ in number of
broken bones (n 17, 2 0.059, df 1, P 0.8),
contusions (n 5, 2 0.2, df 1, P 0.655), scars
of unknown cause (n 13, 2 0.077, df 1, P
0.782), or incidence of severe chronic or acute pain
(n 22, 2 1.64, df 1, P 0.2), although the
sample size for each was relatively small (Table 2).
Soft-tissue wounds
As a class, soft-tissue wounds involving rupture of
the epidermis and/or additional tissue not caused by
animal bites or stings or resulting in significant
ancillary infection (i.e., health insult coded as laceration,
puncture, contusion, or abrasion) accounted
for 301 (46%) of the 678 pathological conditions observed.
Significantly more soft-tissue wounds were
observed than infections, the next most frequently
observed type of health insult (Table 2, 2 45.275,
df 1, P 0.000). Soft-tissue wounds ranged from
small abrasions or cuts to serious wounds (e.g., accidental
finger amputation, heel slashed to bone, or
5-inch-long gash in thigh). If serious infection was
reported, the health insult was coded as infection
because this was usually the more serious condition.
Fourteen incidences of soft-tissue wounds resulted
in serious subsequent bacterial infection, or 4.44% of
the 315 primary soft-tissue rupture wounds recorded.
Lacerations were significantly more prevalent
than other types of soft-tissue wounds, followed by
puncture wounds, abrasions, and contusions ( 2
411.31, df 3, P 0.000). Sampling bias may account
for some of this difference: contusions can only
be seen if the injury is current, and abrasions may
be less likely to leave scars than lacerations. Nevertheless,
the two most prevalent causes of soft-tissue
wounds (machete cuts and injury from branches,
sticks, and logs) are also the most frequently cited
causes of soft-tissue trauma overall, and these
sources of injury appear more likely to cause laceration
than contusion or abrasion. The vast majority
of lacerations were attributable to accidental causes:
machete (46%), running into, being hit by, falling on,
or stepping on branches, sticks, or logs (16%), knife
(6.5%), axe (4.2%), and lance (3.7%). However, nine
lacerations (4%) were sustained during interpersonal
violent encounters (Table 3).
All observed puncture wounds stemmed from accidental
causes. These included punctures from
spines (38.9%), branches or sticks (36%), lances
(8.3%), fish spines (2.78%), and harpoons (2.78%),
with the remaining 8.3% coming from unidentified
TABLE 1. Age/sex Distribution of Subjects
causes. Similarly, all observed abrasions were due to
accidental causes: branches, sticks, logs, spines,
falls, and a fingernail. Finally, of the five contusions
observed, three were due to accidents and two to
interpersonal violence.
Infections (including infectious disease, parasitic
infection, and bacterial infection of wounds) were
the second most common general class of pathological
condition observed, accounting for 157 of the 678
pathologies in the sample (23.2%). While the number
of infections observed did not differ significantly
from the next most frequently observed type of
health insult (bites and stings; 2 0.859, df 1,
P 0.354), infections were more frequently observed
than all remaining types of health insult
combined (i.e., all health insults excluding soft-tissue
wounds and bites/stings; 2 31.55, df 1, P
0.000, Table 2). Nevertheless, infectious disease is
certainly underreported in this sample, since few
leave visible traces and only the most recent or
severe instances are likely to have been recalled or
recorded. For instance, no attempt was made to ask
subjects about common colds or flu, because while
the actual frequency was expected to be high, the
reported frequency was not expected to be accurate.
Conversely, informants were specifically asked if
they had suffered from the following infectious diseases
or parasitic infections known to occur in Shiwiar
territory: measles, pertusis, tuberculosis, varicella,
leishmaniasis, and malaria.
Parasites accounted for 94 of 157 infections recorded
(60%). Ectoparasites were the most common
form of infectious condition, accounting for 63% of
parasitic infections and 37.6% of infectious conditions
overall (Table 4). Ectoparasites were coded
based on their having left visible scars. Informants
noted that these scars were usually the result their
having scratched the skin off the affected area, causing
minor secondary bacterial infection or delaying
the healing process. None of these infections were
reported as serious; nor was there visible evidence
that they were. Common ectoparasites endemic to
the study area include mosquitoes, no-see-ums, chiggers,
ticks, and bot flies. Although some types of
ectoparasites can cause disabling bacterial infection
if left untreated (e.g., major infestation of sand flea
larvae reportedly caused death among some Yanomamo
orphans; Chagnon, 1992; Hagen et al., 2001),
none of those reported here caused significant infection.
Endoparasitic infection accounted for the remaining
37% of parasitic conditions, and 22.3% of
infectious conditions overall. While gastrointestinal
amoebas, giardia, and worms are endemic in this
population, these were not recorded because it was
impossible to get accurate or verifiable reports of
periodic bouts of symptomatic diarrhea. The exception
to this was a current case of amoebic dysentery
observed at the time of the study.
Malaria (Plasmodium vivax) occurs in periodic
outbreaks in the study area. Bouts of malaria, including
when they occurred and whether they resulted
in disability, were commonly recalled and
corroborated by other informants. Eighteen of the 39
individuals surveyed (46%) had suffered from malaria,
often in recurring bouts. In addition, 11 individuals
showed evidence of and/or reported leish-
TABLE 2. 2 tests, frequency of health insult by type and sex of victim
Female Male 2 for sex differences
Total: column,
2 1,861, df 16,
p 0.000
Observed Expected Observed Expected 2 df P-value Total observed Total expected
Laceration 77 113.0 148 113.0 21.68* 1 0.000 2261 39.9
Infection 62 78.5 95 78.5 6.94* 1 0.008 1571,2,b1 39.9
Bite/sting 52 74.0 96 74.0 13.08* 1 0.000 1482 39.9
Puncture wound 12 20.0 28 20.0 6.4** 1 0.011 40 39.9
Abrasion 8 15.0 22 15.0 6.53** 1 0.011 30 39.9
Pain 14 11.0 8 11.0 1.64 1 0.2 22b2 39.9
Fracture 8 8.5 9 8.5 0.059 1 0.8 17b1 39.9
Burn 3 6.5 10 6.5 3.77 1 0.052 13b2 39.9
Scars unknown 6 13.0 7 13.0 0.077 1 0.782 13b2 39.9
Contusion 2 2.5 3 2.5 0.2 1 0.655 5 39.9
Arthritis 1 0 0.03 1b2 39.9
Bleeding 1 0 0.03 1b2 39.9
Blisters 0 1 0.03 1b2 39.9
Concussion 0 1 0.03 1b2 39.9
Irritation 1 0 0.03 1b2 39.9
Sprain 0 1 0.03 1b2 39.9
Swelling 0 1 0.03 1b2 39.9
Total 248 430 339.0 48.455* 1 0.000 678 678.0
1 2 50.568, df 1, P 0.000.
b1 vs. b2 2 50.568, df 1, P 0.000.
2 2 0.859, df 1, P 0.354.
3 Expected frequency less than 5, no 2 test performed.
* Significant at P 0.01 level.
** Significant at P 0.05 level.
maniasis (28%); 8 of these individuals were
eventually treated with a course of medication, although
some did not complete the course of injections
necessary for a full cure. Evidence of onchersoriasis
(river blindness) was seen in three
individuals. Finally, one individual had an infestation
of a large unidentified “worm” in the chest area,
which ultimately required surgical removal at a mission
Infectious disease was the second largest class of
infectious condition, accounting for 24% of instances
recorded. Of the 39 individuals for whom data on
disease was recorded, 49% had suffered varicella
(chickenpox), 28% sarampion (measles), 5% pertusis,
and 2% clear symptoms of later-stage tuberculosis;
23% were vaccinated against measles. In addition,
13% reported cases of severe febrile or other
illnesses whose specific medical cause could not be
identified based on informants’ descriptions (informants
referred to these, along with most other serious
conditions, as the product of shamanistic attacks).
Twenty-five cases of bacterial infection significant
enough to result in either drainage of puss or other
clear evidence of infection (e.g., tissue inflammation
or stench) were recorded in the sample: 14 were
subsequent to accidental laceration (6% of lacerations
observed), and 11 were from nonaccidental
causes. One of the latter, an abscessed tooth severe
enough to be draining pus and causing extreme pain
TABLE 3. Frequency of soft-tissue wounds by type and cause
Pathology Type Cause Female Male Total
Laceration Accident Machete 35 64 99
Branch/stick/log 11 24 35
Na 15 16 31
Knife 7 7 14
Axe 2 7 9
Fall 8 8
Lance 8 8
Collision 2 2
Hit 2 2
Kicked 2 2
Spine 2 2
Blowgun 1 1
Nail 1 1
Howler monkey 1 1
Accident total 70 145 215
Unknown Unknown 1 1
Violence Assault (unarmed) 2 2
Light (unarmed) 2 1 3
Machete 2 2 4
Violence Total 6 3 9
Laceration total 77 148 225
Puncture Accident Spine 3 11 14
Branch/stick/log 6 7 13
Fall 1 1
Lance 3 3
Unknown 3 3
Fish spine 1 1
Harpoon 1 1
Accident total 9 27 36
Unknown Unknown 3 1 4
Unknown Total 3 1 4
Puncture total 12 28 40
Abrasion Accident Spine 10 10
Branch/stick/log 2 5 7
Unknown 4 3 7
Fall 1 3 4
Fingernail 1 1 2
Accident total 8 22 30
Abrasion total 8 22 30
Contusion Accident Branch/stick/log 1 1
Fall 1 1
Hit 1 1
Accident total 3 3
Violence Assault 1 1
Fight 1 1
Violence total 2 2
Contusion total 2 3 5
Grand total 99 201 301
for months until it could be treated by a dentist, was
current at the time of the study (for a systematic
comparative study of dental health including this
population, see Walker et al., 1998).
Bites and stings
Bites and stings are ubiquitous features of life in
the field area. Most of these come from ectoparasitic
insects (see above). People also suffer numerous
stings from bees and wasps present in vast swarms
during the dry season. One can hardly sit down or
lean against something in the house during the
height of the dry season without being stung by a
wasp. These stings are too prevalent to accurately
record and do no significant damage other than minor
pain and localized swelling. However, the sting
of one species of ground-living wasp, the conga,
causes severe pain lasting several hours. By 1998,
Africanized bees were reported to have entered the
study area and to have inflicted serious injury on a few
individuals; to date, no deaths have been reported.
The vast majority of animal bites come from vampire
bats, and the majority of victims were young
children (predominantly boys) who, according to informants,
slept either without mosquito nets or fitfully,
thus exposing their bodies to the bats (Table
5). At the time of the study, rabies was not reported
to be widespread in the study area; however, in
1997, rabies transmission by vampire bats to cattle
was reported just north of the study area.
Although I have seen scorpion stings and caterpillar
toxin cause extreme pain and disability lasting
up to 2 days, by far the most significant risk of
bites/sting in the study area comes from venomous
snakes. Snakebite continues to be a significant
cause of death worldwide, and specific adaptations
designed to reduce its occurrence are posited for
humans and other primate species (e.g., Cook and
Mineka, 1991; Mineka and Cook, 1988). The Ecuadorian
Amazon is home to numerous widely distributed,
deadly species. Fourteen of the individuals
sampled suffered 18 cases of snakebite (Table 5): 4
were treated with antivenin, 2 do not appear to have
resulted in significant amounts of envenomation,
and 12 were untreated at the time of the bite or were
TABLE 4. Frequency of infections by type and cause
Pathology Type Cause Female Male Total
Infection Accident (bacterial) Machete 2 2 4
Spine 4 4
Branch/stick/log 1 1 2
Unknown 1 3 4
Accident total 4 10 14
Bacteria (nonaccidental) Injection 6 3 9
Ear piercing 1 1
Abscessed tooth 1 1
Bacteria total 9 3 11
Varicella 12 7 19
Measles 5 6 11
Unknown 2 3 5
Pertusis 2 2
Tuberculosis 1 1
Disease total 22 16 38
Ectoparasite Insect (various) 10 48 58
Bot fly 1 1
Ectoparasite total 10 49 59
Endoparasite Malaria 8 10 18
Leishmaniasis 5 6 11
Onchersoriasis 3 3
Ameoba 1 1 2
Worm 1 1
Endoparasite total 18 17 35
Parasite total 28 66 94
Grand total 62 95 157
TABLE 5. Frequency of bites and stings by type and cause
Pathology Type Cause Female Male
Bite/sting Bite Ant 1 1
Bat 27 75 102
Dog 1 1 2
Fish 2 2
Insect 5 5 10
Lizard 1 1
Person 1 1
Pig 1 1
Piranha 1 1
Snake 11 7 18
Squirrel 2 2
Bite total 46 95 141
Sting Bee 1 1
Scorpion 5 1 6
Sting total 6 1 7
Grand total 52 96 148
treated by shamans. While shamans are clearly effective
in treating certain conditions (e.g., controlling
bleeding, setting broken bones, or preventing
infection of lacerations), and medicinal plants appear
to be effective in treating malaria and dysentery
among adults (albeit with harsh side effects),
there is no evidence of effective shamanic curing of
snakebites among the Shiwiar.
Other health insults
Chronic or prolonged pain (22 cases), bone fractures
(17 cases), burns (13 cases), and a variety of
other conditions round out the pathological conditions
observed in this sample (Table 6). Because
pain was often subsequent to or associated with
other conditions, reports of pain are here limited to
conditions extending longer than, or aside from, the
primary condition. For instance, the case of pain
caused by snakebite recorded here (Table 6) is not
primary pain engendered by the bite, but chronic
pain suffered as a consequence of walking upon a
limb deformed by snakebite.
Of 17 broken bones recorded, 15 (88%) were sustained
in accidents, and 2 (12%) were sustained
during fights. Reports of broken bones were verified
by cross-checking with other informants, and by
feeling for evidence of a healed fracture. Broken
bones are sometimes set by a shaman, some of whom
are reportedly skilled at this procedure.
Frequency, cause, and duration of disability
Informants from one sample village were asked
the duration of disability, if any, associated with
each health insult reported, and this information
was then cross-checked with other informants. The
Kruskal-Wallis test indicates that the sex composition
of this subsample, including 8 males and 9
females, does not differ significantly from the rest of
the larger sample ( 2 0.100, df 1, P 0.725),
although it does contain an older age cohort (comprised
mostly of individuals over age 15 years; 2
14.31, df 1, P 0.000). Estimates of disability
TABLE 7. Duration of disability by frequency of occurrence
(days) Frequency Percent
0 129 60.0 60.0 40.0
1 8 3.7 63.7 36.3
2 8 3.7 67.4 32.6
3 2 0.9 68.4 31.6
4 1 0.5 68.8 31.2
6 1 0.5 69.3 30.7
7 12 5.6 74.9 25.1
10 1 0.5 75.3 24.7
11 1 0.5 75.8 24.2
12 1 0.5 76.3 23.7
14 7 3.3 79.5 20.5
15 4 1.9 81.4 18.6
17 1 0.5 81.9 18.1
20 1 0.5 82.3 17.7
21 5 2.3 84.7 15.3
23 1 0.5 85.1 14.9
30 17 7.9 93.0 7.0
45 4 1.9 94.9 5.1
60 4 1.9 96.7 3.3
90 1 0.5 97.2 2.8
180 1 0.5 97.7 2.3
365 1 0.5 98.1 1.9
Chronic 4 1.9 100.0 0.0
Total 215 100.0
TABLE 6. Frequency of pain, fracture, burn, and other conditions by type and cause
Pathology Type Cause Female Male Grand total
Pain Accident Unknown 1 1
Bite Snake 4 4
Disease Unknown 3 1 4
Unknown Unknown 2 2 4
Pregnancy Birth complications 9 9
Pain total 14 8 22
Fracture Accident Branch/stick/log 2 1 3
Unknown 2 1 3
Fall 3 4 7
Collision 2 2
Violence Fight 1 1 2
Fracture total 8 9 17
Burn Accident Fall 1 1
Fire 3 8 11
Shotgun 1 1
Burn total 3 10 13
Scars unknown Accident Unknown 1 1
Unknown Unknown 6 6 12
Scars unknown total 6 7 13
Arthritis Disease Arthritis 1 1
Bleeding Pregnancy Birth complications 1 1
Blisters Unknown Blisters 1 1
Concussion Accident Collision 1 1
Skin irritation Unknown Unknown 1 1
Sprain Accident Unknown 1 1
Swelling Bite Snake 1 1
Grand total 34 38 72
duration were most often reported by informants in
even units of days, weeks, or months. These were
converted to number of days for presentation. Table
7 shows the frequency with which disabilities of
various durations were reported. Most incidents recorded
were minor and resulted in no disability. Of
the 215 health insults recorded in this subsample,
86 (40%) resulted in disability lasting a day or
longer that could be confidently established, 66
(30.7%) resulted in disability lasting a week or
longer, 51 (23.7%) lasted 14 days or longer, and 32
(14.9%) lasted a month or longer (Table 7). In addition,
four pathological conditions were chronic and
resulted in a reported periodic disability of varying
unspecified durations.
Table 8 indicates the types of health insult resulting
in disability in this subsample. Included are 28
infections (13.02% of total cases in the subsample),
15 bites (6.97%), 13 cases of debilitating pain
(6.05%), 11 broken bones (5.12%), 10 lacerations
(4.65%), 4 stings (1.86%), and one burn, one puncture
wound, one case of postpartum bleeding, and
one case of multiple simultaneous contusions of unknown
origin (attributed to shamanistic attack).
Those that caused prolonged disability of 2 weeks or
longer include 10 of the 11 broken bones, 9 bites (8 of
11 of which were snakebites), 6 lacerations, 6 cases
of malaria, 5 bacterial infections stemming from
lacerations or puncture wounds, 3 infectious diseases
of unknown type, 2 cases of postpartum complications
(one near-lethal blood loss, and one severe
pain), one multiple contusion, one abscessed tooth,
one acute pain from disease of unknown type, one
amoebic infestation, and one puncture wound. Additionally,
knee injury, tooth abscess, snakebite,
stroke, malaria, whooping cough, postpartum infection,
respiratory ailment, and severe foot fungus
resulting in periods of disability ranging from 5 days
to a year were observed during four study periods
between 1994–1998, but victims were not part of the
sample included here. In contrast, broken fingers,
severe beating resulting in black eyes and facial
contusions, bites from vampire bats, a laceration in
which the tip of a machete was imbedded in the chin,
severe laceration of the hand, and a puncture wound
from a thorn passing through the thumbnail into the
thumb, observed over the same period, did not result
in observable disability. Victims of these incidents
continued working, with only minor pause to treat
the wound.
When they occur, some types of injury/illness are
significantly more likely to cause disability than expected
if all pathologies are equally likely to cause
disability (for pathologies resulting in disability,
2 20.06, df 9, P 0.018). Table 9 indicates both
the observed and expected frequency of disability by
type of health insult for the subsample, as well as
results of relevant chi-square tests for disabling conditions
that could contribute to the overall effect. As
one would expect, when they occur, fractures are
significantly more likely to result in disability than
expected by relative prevalence in the subsample
( 2 11.438, df 1, P 0.001). Conversely, lacerations
appear to be less likely to cause disability
than expected ( 2 5.675, df 1, P 0.017). This
is likely due in part to the high prevalence of minor
lacerations which nevertheless leave scars, and local
skill at stopping bleeding and infection from lacerations.
Neither infections nor pain result in significantly
more or less disability than expected by their
prevalence in the subsample ( 2 1.986, df 1, P
0.159; 2 0.693, df 1, P 0.405, respectively).
Snakebite is highly likely to cause long-term disability.
Ten cases for which duration of disability
was estimated and cross-checked were recorded. In
four of these instances, antivenin was administered.
Eight of the 10 cases accounted for 502 days of
disability, with one case resulting in permanent disfigurement
of the victim’s foot. This and another
case resulted in major tissue necrosis and gangrene,
resulting in disability of a year and 6 months, respectively.
The foot disfigurement resulted in a life-
TABLE 8. Frequency of disability duration by pathology
Pathology Duration in days Number of cases
Bite/sting 1 5
3 1
7 3
21 2
30 2
45 1
60 2
90 1
180 1
365 1
Bleeding 30 1
Fractures 7 1
14 3
15 1
20 1
21 1
30 3
45 1
Burn 7 1
Concussion 3 1
Contusion 30 1
Infection 1 3
2 1
6 1
7 4
10 1
12 1
14 2
15 3
21 2
30 7
45 2
60 1
Laceration 4 1
7 3
11 1
14 1
23 1
30 2
60 1
Pain 2 7
17 1
30 1
Chronic 4
Puncture 14 1
Total 86
long reduction in mobility due to a pronounced limp,
as well as ancillary pain during travel. Interviews
and observation indicate that this limp resulted in
an impaired gait and curtailment of activities for
which quick movement is necessary (e.g., felling
large trees, pursuit of game with hunting dogs), as
well as limiting the victim’s ability to carry heavy
loads and walk long distances at normal speed without
Demographic and fitness effects of provisioning
during healthcare crises
As of 1998, the resident population of the Shiwiar
core study area in Ecuador was 410 persons living in
six villages (one outside officially designated Shiwiar
territory), with an additional 87 siblings or
offspring of core Shiwiar individuals living in surrounding
villages. While 166 persons make their
home in the two villages from which illness and
injury data were collected (63 and 103, respectively),
the number of people resident in the villages at any
given time varies, as people go visiting or on extended
foraging trips. The sample of 40 individuals
thus represents 24% of the total population in these
villages, and 10.25% of the population of the core
study area. The 17-person disability sample represents
16.5% of the population of village two.
Both short- and long-term disability were widely
distributed across individuals in the subsample: 16
of 17 individuals reported disability lasting 7 days or
longer (94%), 15 reported disability of 14 days or
longer (88%), and 11 reported disability of 30 days or
longer (64.7%) (Table 10). A specific age of occurrence
was reported for 131 of 215 pathological conditions
recorded; 51 of these were cases in which
disability was observed. There is no significant cor-
TABLE 9. Chi-square tests for frequency of disability by health insult1
Observed N Expected N Residual Chi-square df P value
Bite/sting 19 18.0 1.0
Bleeding 1 0.4 0.6
Fracture 12 4.9 7.1 10.858* 1 0.001
Burn 1 0.4 0.6
Concussion 1 0.4 0.6
Contusion 1 0.8 0.2
Infection 27 30.7 3.7 0.693 1 0.405
Laceration 10 19.2 9.2 5.675* 1 0.017
Pain 13 9.0 4.0 1.986 1 0.159
Puncture 1 2.0 1.0
Total 86 20.060* 9 0.018
* Statistically significant at P 0.05.
TABLE 10. Frequency and duration of disability by individual and reproductive success
ID no. Age Sex
Disability duration (days) RS (descending generations)
Descendants %
Total 7–13 14–29 30 1st 2nd Total In village % village
% Total
8 16 f 2 1 1 0 0 0 0 0 0.0 0.0
53 18 f 8 2 3 2 0 0 0 0 0.0 0.0
101,3 18 f 3 0 1 1 2 0 2 2 1.94 0.40
63 25 f 1 0 0 1 0 0 0 0 0.0 0.0
161–3 27 f 6 0 1 3 2 0 2 2 1.94 0.40
121–3 29 f 14 1 1 4 85 0 8 85 7.78 1.61
111,2 37 f 4 1 0 3 94 51 14 74 6.80 2.82
21–3 43 f 10 2 3 5 10 8 18 15 14.56 3.6
17 7 m 2 0 2 0 0 0 0 0 0.0 0.0
153 15 m 5 0 3 2 0 0 0 0 0.0 0.0
11,3 22 m 4 2 0 2 2 0 2 2 1.94 0.40
71 24 m 7 1 5 0 3 0 3 3 2.91 6.0
143 34 m 1 0 0 0 95 0 9 95 8.74 1.81
31,2 36 m 1 na na 1 3 0 3 3 2.91 0.60
41 37 m 3 2 1 0 5 1 6 6 5.83 1.20
91 43 m 3 2 0 0 94 56 14 74 6.80 2.82
131,3 50 m 8 1 1 3 11 14 25 24 23.30 5.03
Total 82 15 22 27 54* 28* 82* 73* 70.87* 16.49*
1 Individuals who had begun reproduction by time of study.
2 Individuals who suffered pathology likely to be lethal without provisioning after age of first reproduction (during socially recognized
3 Individuals who suffered pathology likely to be lethal without provisioning before age of first reproduction.
4 Represents identical individuals: offspring of a married couple, both included in sample.
5 Eight of these 9 are identical individuals: offspring of a married couple, both included in sample.
6 Represents identical individuals.
* Totals calculated based on descendants of a couple, both of whom are included in subsample only once.
f, female; m, male.
relation between age at which a health insult occurred
and duration of disability (r2 0.105, P
In addition to the 51 cases of disability for which
an age of occurrence estimate was available, seven
cases of disability were identified as occurring during
“childhood” or before the birth of the victim’s
firstborn child. Because complete genealogical data
are available for all individuals in the subsample, it
was possible to calculate whether or not an individual
had entered the reproductive stage of the life
cycle, and if so, the number of offspring who survived
prior to the injury or illness for 59 cases of
disabling event occurring in the subsample
(Table 11).
At present, small population size and limited genealogical
knowledge for ascending generations
(largely the result of scattered settlement and locally
endogamous marriage) mean that the data are
insufficient to calculate age-specific Shiwiar mortality
rates at this time. However, comparing the age of
disability occurrence with genealogical data allows a
calculation of the probable effects of disability on
reproduction and mortality. Thirty-three of 59
(55.9%) cases of disability affected individuals prior
to first reproduction, and 26 of 59 (44%) affected
individuals after first reproduction. The former include
one unmarried woman with no children who,
at 26, was well past the usual age of marriage.
Duration of these cases ranged from 1–365 days,
with 13 of the 33 prereproduction (22%) and 14 of
the 26 post-first-reproduction cases (53.85%) causing
disability of 1 month or longer. The 13 prereproduction
incidents were distributed among 9 of 17
individuals (52.94%) for whom data was available.
The 14 post-first-reproduction incidents were distributed
among 5 of 12 individuals in the subsample
who had begun reproduction at the time of the study
(42%). Of these 5 individuals, none were each other’s
mate. Two of these 5 people do have offspring with a
person in the sample who did not suffer life-threatening
health crises during their lifetime (Table 10).
If provisioning is required for individuals to survive
disability of 30 days or longer, then 11 of 17
individuals in the subsample (64.7%) would have
died prior to the study period (5 of whom had begun
reproduction by the time of the study). Without provisioning,
even if 1) all other living individuals in
the village suffered no significant health insults and
therefore no higher rate of mortality, and 2) there
was no increase in juvenile mortality or decrease in
births associated with increase in adult mortality,
then 6.6% of the village population would not be
alive due to mortality stemming from lack of provisioning.
This estimate is extremely conservative.
Using age of disability occurrence in combination
with genealogical data makes it possible to calculate
the number of surviving offspring and grand-offspring
who would not have been born without
healthcare provisioning. Fifty-four offspring and 28
grandchildren were born to individuals in the sample
(children/grandchildren born to parents/grandparents
who are both in the sample were counted
only once). However, only two members of the sample
had completed or were approaching probable
completed fertility. Further, several reproductiveage
individuals in the sample were descendants of
others in the sample. The demographic, settlement,
and marriage structure of the Shiwiar population
(matrilocal residence, long period of bride-service,
and preferential cross-cousin marriage) means that
a significant proportion of the local population is
descended from only a few individuals. Thus, strategic
healthcare altruism will have large effects on
subsequent generations and the population structure
as a whole. Forty-six of the 54 (82%) members
of the first descending generation of sample individuals
were born to individuals after the person survived
an incident likely to be fatal without healthcare
provisioning. Twenty-seven of 28 (96.4%)
TABLE 11. Duration of disability by age of occurrence in reproductive lifespan
Duration (days)
Juvenile 21 22 23 24 25 26 27 28 30 35 37 39 41 43 Total
1 4 1 5
2 1 1
3 1 1 2
4 1 1
6 1 1
7 6 1 1 1 1 1 11
10 1 1
14 2 2 1 1 1 7
15 3 1 4
17 1 1
20 1 1
21 2 1 3
30 7 1 1 1 1 11
45 2 1 3
60 1 1 1 1 4
90 1 1
180 1 1
365 1 1
Total 33 3 3 3 1 1 3 1 2 1 1 2 1 1 3 59
members of the second descending generation were
born after a direct ancestor in the sample survived
such an incident. In fact, three sample individuals
(i.d. numbers 2, 11, and 13, one of whose mate is also
included in the sample) who survived health crises
expected to be lethal without healthcare provisioning
are either the mother or grandparent of the 27
second-generation descendants. Overall, these three
individuals are either the parent or grandparent of
46 of the subsample village residents (45%), and
11.5% of the Shiwiar population in the study area.
One (i.d. no. 13), is the parent or grandparent of 23%
of the subsample village and 5% of the Shiwiar population
block. Another (i.d. no. 2) is the direct ancestor
of 14.5% of the village and 3.6% of the population
(Table 10).
Strategic healthcare allocated to two of these people
had enormous demographic and political influence.
The first individual (no. 13) suffered a year of
disability due to snakebite as a young man. Tissue
necrosis and nerve damage left him with a deformed
foot. During times of intense warfare in which his
father, a noted shaman and warrior, was specifically
targeted and eventually killed, this man was shuttled
by allies from house to house across Shiwiar
territory during the time he was disabled. Not all
individuals are provided with this extreme level of
care. Even though disabled, the man later distinguished
himself as a warrior, and as a young man
was called to live with his mother-in-law as headman
of the village in which he now resides. He is
now one of the two juunt (big men or elders) of this
village. The second individual (no. 2) is his sister-inlaw:
their kin group forms the basis for one of the
two dominant coalitions in the Shiwiar study area.
Decreased extrinsic mortality is a key feature distinguishing
human life history from that of other
hominoids, yet how this is achieved has received
little attention. The data presented herein indicate
that provisioning to sick or injured individuals has
large fitness benefits for the recipients, and that
incidents resulting in potentially fatal disability occur
with sufficient frequency that health aid effectively
reduces extrinsic mortality in this population.
To the extent that the evolution of long human lifespan,
delayed maturity, and the distinctive set of
subsistence, social, reproductive, and mental traits
hypothesized to have coevolved with them are predicated
on the evolution of decreased mortality, then
the evolution of provisioning during health crises
likely played a significant role in their evolution.
The data presented here were gathered via methods
designed to provide evidence of incidence, duration,
and fitness effects of healthcare provisioning
among a living forager-horticulturalist population
that can later be compared with prehistoric osteological
remains. Clearly, the Shiwiar do not constitute
a perfect model of other populations: no single
extant or prehistoric group could provide a comprehensive
snapshot of the pathogenic, foraging, social,
and demographic conditions that form the parameters
of our evolutionary history. Nevertheless, the
data presented here provide information regarding
the incidence of soft-tissue injury, disability duration,
and fitness effects of surviving long-term
health insults (data that are difficult to obtain from
osteological remains alone) in a small-scale culture
dependent on foraging for a significant portion of its
diet and with little everyday access to Western medical
Results reported here would lose comparative relevance
for understanding the evolution of mortality
reduction via healthcare provisioning if Shiwiar disabling
conditions were primarily the result of industrial
technology, diseases, or a nonforaging lifestyle.
This is not the case: disabling health insults reported
are not overwhelmingly due to factors directly
associated with Western industrial technology.
While machete wounds (and concomitant
infections) are common, they are more likely to leave
visible evidence than many other types of health
insult (e.g., infectious disease, insect bites, endoparasitic
infection, or influenza), and are therefore
likely to be overrepresented in this sample. On the
other hand, because machete cuts leave clear physical
evidence on the skin, all machete lacerations
causing prolonged disability among sample individuals
were almost certainly recorded. Because Shiwiar
use machetes as general-purpose cutting,
scraping, chopping, and digging tools (and occasionally
in hand-to-hand combat), frequency of exposure
to cutting tools may be expected to be about equal
between machetes and the wood, stone, and bone
tools used before they had access to Western implements.
Specific comparison is needed to determine
whether or not machetes pose a greater or lesser
risk of injury/disability than precontact cutting implements.
On the one hand, stone tool manufacture
and use are expected to result in minor lacerations
from flakes and flake fragments not associated with
machete use, and some of these are expected to
result in infection. On the other hand, efficient use of
the machete for chopping or cutting branches involves
using it with high speed (achieved by a whiplike
use of the blade) to generate high force. Thus,
the most severe machete wounds I have observed,
both in this sample and over the course of ethnographic
fieldwork in general, involve the machete
hitting a branch at an odd angle and ricocheting
with high force into an appendage of the person
wielding it. Because machetes are kept razor-sharp,
the result is a severe laceration cutting deep into the
soft tissue, usually to the bone of the leg or foot.
However, because the sharper the cutting tool, the
more “bite” it obtains and the more precisely it can
be wielded, severe chopping/cutting accidents might
be less likely with a machete than with a stone axe.
Indeed, conventional wisdom in our own culture
cautions that dull tools cause more injury than
sharp ones. In sum, while stone or palmwood axes
might be more likely than machetes to cause injury,
they might be less likely than machetes to cause
deep lacerations (causing contusions or fractures instead).
When they do occur, fractures among the Shiwiar
are more likely to result in long-lasting disability
than are lacerations; the Shiwiar may therefore experience
less long-term disability from tool use than
our hominid ancestors did. Future comparison of the
incidence of fracture between Shiwiar and preindustrial
foragers can help resolve this issue, since nonlethal
fractures leave clear osteological signatures.
Among the Shiwiar, the primary cause of fractures
is collision with logs and branches. Taken together,
naturally occurring causes of laceration (e.g.,
branches, logs, or spines) produced as many cases of
disability lasting a month or longer as Western
tools, even though the former represent a smaller
proportion of total cases observed (13.7% vs. 19.4%,
respectively). Overall, the number of disabilities
lasting a month or longer directly attributable to
industrial technology (two machete lacerations, and
two machete cuts leading to subsequent infection;
14.28%) is less than that from all naturally occurring
sources (85.72%). Furthermore, industrial technology
is less likely to cause disability of a month or
more than expected from its prevalence in this sample
(20.6% vs. 79.4%, respectively). Snakebites, fractures,
and infections not associated with steel tool
technology or Western causes are all more prevalent
causes of prolonged disability than machetes, even
in this society where machetes are ubiquitous allpurpose
tools. Snakes arguably present the greatest
threat: snakebite is highly likely to result in disability
and resulted in the longest lasting disabilities.
Results of this study indicate that health risk and
temporary, potentially lethal disability are recurrent
features of Shiwiar life. Disabling conditions
were observed in individuals at all stages of the
lifespan. Almost all individuals suffer a disability
lasting 7 days or longer, almost 90% suffer a disability
of 14 days or longer, and over 60% suffer a
disability of 30 days or longer. Without provisioning,
over 60% of the subsample are unlikely to have
survived, or at the very least, the mortality rate of
the subsample would be much higher. These findings
point to two critical questions: when did healthcare
provisioning arise in hominid prehistory, and
did specific adaptations evolve which function to
elicit and confer provisioning to temporarily disabled
With regard to the first question, results of this
study indicate that chronic conditions are not primary
causes of disability for which individuals require
provisioning from others. Rather, intense
acute conditions are more likely causes of disability
severe enough to require aid. This suggests that, in
seeking evidence for the evolution of mortality reduction
via healthcare provisioning in the hominid
record, investigation should focus on evidence for
acute major trauma or infection which took intermediate
time frames to heal (e.g., Dettwyler, 1991). It is
fairly clear that provisioning during health crises
evolved at least by the time of Homo sapiens neanderthalensis
(Berger and Trinkaus, 1995; Dettwyler,
1991; Trinkaus, 1983). A concerted effort should
therefore be made to compile available data to test
this issue using Homo erectus remains, i.e., the time
frame at issue in the debates about the evolution of
distinctively human life history (e.g., Hawkes et al.,
1998; Kaplan et al., 2000).
The second question has begun to be addressed
elsewhere, but the results reported herein suggest
that further work on the issue is needed. Here I
summarize one set of hypotheses about adaptations
for healthcare provisioning, as a stimulus to additional
research. Once the ability to provide effective
provisioning to sick or injured individuals arose,
then evolutionarily stable strategies for increasing
the likelihood, level, and duration of such care are
expected to have evolved (Kaplan et al., 2000; Sugiyama,
1996; Sugiyama and Chacon, 2000). One proposal
is that the provisioning of fitness benefits to
other individuals makes the provider an important
social resource to the recipients, such that recipients
are motivated to provide long-term provisioning to
the provider when he or she is sick, injured, or
otherwise disadvantaged (Dettwyler, 1991; Kaplan
and Hill, 1985; Sugiyama, 1996; Sugiyama and Chacon,
2000; Tooby and Cosmides, 1996). Gurven et al.
(2000) expand upon these and related ideas, arguing
that the relative proportion of an individual’s kills
transferred to a recipient provides a clear signal of
the provider’s “generosity,” which can be seen as an
indicator of the provider’s commitment to the recipient’s
interests (see also Sugiyama, 1996; Sugiyama
and Chacon, 2000; Sugiyama and Scalise Sugiyama,
2003). Zahavi and Zahavi (1997) argue that, the
more costly a signal, the more confidence can be
placed in its “honesty” because the very cost of the
signal makes it unprofitable to fake. Recipients of
the signal benefit because they receive reliable information
about the quality being signaled. Benefit
transfers can provide a costly signal of both intent
and value as a coalitional ally (e.g., Hawkes and
Bird, 2002; Zahavi and Zahavi, 1997).
Most relevant work on benefit transfers among
foragers focuses on food transfers. The most widely
cited explanations for asymmetric food transfers
(kin selection, reciprocal altruism, foraging risk reduction,
and “showing off”) leave unexplained variance
in food transfer behavior (e.g., Bird et al., 2002;
Bird and Smith, 2001; Hawkes, 1991; Hawkes et al.,
1997, 2001; Kaplan and Hill, 1985; Sugiyama, 1996;
Wiessner, 2002; Winterhalder, 1996). Gurven et al.
(2000) showed that slightly over half the food given
to temporarily disabled Ache foragers is predicted by
the generosity of food sharing exhibited by the disabled
individual when he/she is healthy. Other important
benefits can be given to others besides food,
and generous provisioning of these is also expected
to result in increased solicitude to those who provide
them (e.g., Dettwyler, 1991; Gurven et al., 2000;
Sugiyama, 1996; Sugiyama and Chacon, 2000;
Tooby and Cosmides, 1996).
While some researchers have discounted “risk reduction
hypotheses” for explaining some of the unexplained
variance in food transfers, these researchers
focus on whether food sharing functions to
reduce day-to-day foraging risk, expecting balanced
reciprocity over time (e.g., Bird et al., 2002; Hawkes
and Bird, 2002). Health insurance models also suffer
because individuals are expected to discount future
healthcare benefits against the current cost of maintaining
alliances with potential healthcare providers,
and the probability that healthcare aid will be
needed. It is fairly clear, however, that balanced
reciprocity is unlikely to solve the health risk problem
(Sugiyama, 1996; Sugiyama and Chacon, 2000),
and from this perspective, the generous consistent
conferral of benefits to others does not reap enhanced
healthcare provisioning based on the logic of
reciprocal altruism. Rather, those who honestly signal
positive coalitional intent through costly benefit
transfers to others are for that very reason important
individuals for those to whom they signal: reliable
allies or “true friends” are a real benefit (e.g.,
Gurven et al., 2000; Sugiyama, 1996; Tooby and
Cosmides, 1996). The cost is an expected feature of
signal quality regarding coalitional intent (e.g., Gintis
et al., 2000; Hawkes and Bird, 2002; Zahavi and
Zahavi, 1997). Additionally, those who receive signals
of generosity gain not only a coalitional signal,
but the benefits conferred as a signal of coalitional
intent, and should therefore be even more highly
motivated to retain access to those benefits if they
are threatened. A major threat to future access to
those benefits occurs when their provider is grievously
injured. Healthcare to an individual who has
been consistently generous to you is one way to
buffer this threat. The recipient of costly signals of
intent thus receives generously confered benefits in
a manner closer to byproduct mutualism than to
reciprocal altruism per se. This is because the value
of benefits conferred loses signal value if they are
“repaid.” Finally, results from this study indicate
that the future probability that one will need lifesaving
healthcare aid is high, as are the fitness
benefits of receiving extended care. To date, only
Gurven et al. (2000) have attempted a direct test of
the health-risk buffering or signaling-generosity hypothesis.
As noted, results from that study lend support
to the health-risk buffering hypothesis. Given
the importance of mortality reduction to the evolution
of human life history, it seems that further
testing of health-risk buffering aspects of cooperative
signaling is warranted.
Mortality reduction is a critical factor allowing the
evolution of delayed maturity, long lifespan, and a
variety of distinctive human traits. As extrinsic mortality
decreases, relative fitness benefits of delayed
maturity and long lifespan increase due to the increased
probability of living long enough to realize
fitness benefits from investments in further growth,
production, and/or skill and knowledge acquisition.
In turn, the fitness benefits of investment in longterm
foraging cooperation, and/or noncontingent,
asymmetric, and/or intergenerational food transfers
may also increase, due to an increased probability
that the individual will live long enough to realize
the payoffs of these investments. As Hill and Kaplan
(1999) noted, understanding the evolution of decreased
human mortality is therefore central for
understanding basic features of human evolution.
Results from this study indicate that 1) sickness
and injury occur with significant frequency throughout
the lifespan; 2) these periods are temporally
unpredictable; 3) these periods are not primarily
attributable to impacts from the Western/industrial
world; 4) males suffer more health insults than females;
5) most living individuals suffer health crises
during their lifetimes that are likely to have been
lethal without extended provisioning; 6) provisioning
during health crises reduces mortality in this
population; and 7) the Shiwiar population structure
and lifeway are dependent on infrequent but extended
provisioning to temporarily disabled individuals.
Evidence regarding the frequency, duration, and
fitness effects of disabling conditions in forager and
forager-horticulturalist societies with little access to
Western medicine is sparse. Given this, as well as
the well-developed literature in paleopathology and
the hypothesized importance of health risk for the
evolution of human sociality, studies such as this
one would be profitably added to the basic data
collected on all remaining foraging and forager-horticulturalist
societies. Comparative data to estimate
disability risk, actual rates of mortality reduction
via healthcare provisioning, and the relative fitness
benefits of healthcare altruism within specific populations
are needed to estimate the probable
strength of selection pressure from health risk.
Compilation of hominid evidence for acute disabling
health insults of more than a month’s duration is
needed to identify the emergence of provisioning
during health crises. Finally, further testing of hypotheses
about specific health-risk buffering adaptations
is warranted.
Phil Walker provided data-recording forms, inspiration,
and methodological advice. John Tooby, Leda
Cosmides, and Napoleon Chagnon provided encouragement
and insight. Darcy Hannibal and George
Pryor assisted with data input and organization.
Michelle Scalise Sugiyama provided indispensable
editorial advice. Debbie Guatelli-Steinberg, Joanna
Lambert, John Lukacs, and two anonymous reviewers
provided valuable comments on previous versions
of the manuscript. Of course, any errors are
my own. Alas de Socorro generously included me on
their flight schedules. I extend particular thanks to
the pilots who have risked and lost their lives providing
emergency flight services to the indigenous
people of eastern Ecuador. The generosity, patience,
and good humor of the Shiwiar participants made
this research possible.
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