22-01-2013, 11:39 AM
Modeling Growth and Senescence in Physical Performance Among the Ache of Eastern Paraguay
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ABSTRACT
This article seeks to partially fill a paucity of available data on physical performance
in hunter–gatherer societies. Quantitative data are presented on various physical performance
measures conducted on the Ache of eastern Paraguay, hunter–gatherers up to the 1970s and
now part-time foragers and horticulturists. The performance battery was conducted on most
individuals over 10 years of age, allowing for cross-sectional examination of growth and senescence
patterns across the lifespan for both sexes. These measures tend to display steep ascents and peak
in the early 20s with slight declines thereafter with age for males, whereas females demonstrate
peaks in performance earlier in life, with lower or no senescence rates thereafter. The result is a
convergence in physical performance between men and women at later ages. We suggest that the
female physiology faces reproductive constraints to performance early in life but shifts allocation
to increased work output later in life during the long human postmenopausal stage. In contrast,
the male physiology maximizes work output in early adult life.
INTRODUCTION
Although anthropometric data such as
body weight, height, and skinfolds are commonly
collected in studies of traditional
societies, we know of only a few anthropological
studies that have conducted age-specific
physical performance studies of foraging
(or part-time foraging) societies. These
include Canadian Inuit (Rode and Shephard,
1971, 1994), children in Botswana (Bock,
1995, 2002), Gidra hunters in Papua New
Guinea (Ohtsuka, 1989), Hadza foragers in
Tanzania (Marlowe, 2000; Blurton Jones and
Marlowe, 2002), and several studies of traditional
societies reviewed by Shephard (1978).
More attention should be given to parametric
modeling of these measures across the lifespan
to allow for closer analysis of growth
and senescence rates and better intergroup
comparisons. Given that the genetic potential
of human physiology evolved in a hunting and
gathering context with high activity levels and
food limitations, we feel information derived
from these studies is critical to understanding
human patterns of growth and senescence
in both ancestral and modern peoples.
Field methods
A physical performance battery was conducted
between May 15 and August 5, 2000,
on nearly all individuals over 10 years of age
living at the Arroyo Bandera colony and
between December 15 and 31, 2000, at
Kuetuvy, a recently established Ache community.
The battery included weight, arm
diameter, grip strength (measured with a
Smedley III), 50-m dash, pushups, pullups,
and chinups. A summed measure of pushups,
pullups, and chinups is a low-cost way
to measure upper body strength, but suffers
from variability introduced by differential
motivation across individuals, as discussed
below. Subscapular and tricep skinfolds
were measured at Arroyo Bandera only. To
increase sample size, weights and grip
strengths were measured among men and
women in a third Ache colony, Chupa Pou.
RESULTS
Table 1 gives means of anthropometrical
measurements broken down into age groups
and Table 2 gives means of physical performance
activities. However, the modeling
approach as described above is preferable to
giving means for 5- or 10-year age intervals
because we are interested in the true shape
of the function and testing hypotheses concerning
differences in the shapes of curves.
Means and standard errors for age intervals
are given for anthropometrics (Table 1) and
physical performance measures (Table 2) to
facilitate comparisons with previous studies
where structural modeling is lacking. Both
absolute and relative (measures divided out
by body weight) are given because we are
interested in both raw performance, driven
largely by body size, as well as performance
per unit of body weight.