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For the study of a species, it is fundamental to
observe it under natural conditions. For the human
species, the closest condition to the natural one is that of
the few residual hunter–gatherer populations, which is
equivalent to the human condition in the Paleolithic peri
od. These populations live in areas of difficult access, and
as such it is very difficult to contact and study them.
Moreover, when they come in contact with “civilized”
subjects, most of them fall victim of infectious diseases
they are not adapted to. It is also worth noting that these
people are illiterate and do not use numbers or have spe
cific memories of past events. The precise study of a
hunter–gatherer population is therefore a formidable sci
entific challenge.
One of the most comprehensive studies in the field
was conducted in the late seventies on a small tribal pop
ulation of Paraguay, the Ache, best known with the depre
ciative name Guayaki used by their “civilized” neighbors.
The report of this study was published in 1996 [1]. Many
of the data are unique or with few matches in other simi
lar studies [24].
In this paper, I want to summarize some of the data
from Hill and Hurtado’s study [1] concerning the life
table of this hunter–gatherer people in wild conditions
and the causes of their mortality. These data will be used
for considerations about the evolutionary hypotheses on
aging phenomenon.
DATA FROM LIFE TABLE OF ACHE PEOPLE
AND THEIR IMPLICATIONS
FOR EVOLUTIONARY HYPOTHESES
ABOUT AGING
Hill and Hurtado’s very demanding study (“fourteen
years of data collection” among the Ache and “nearly five
years of writing” [1]) is a very valuable work and an almost
unique source of information. Such a study would be
ISSN 00062979, Biochemistry (Moscow), 2013, Vol. 78, No. 9, pp. 10231032. © Pleiades Publishing, Ltd., 2013.
Published in Russian in Biokhimiya, 2013, Vol. 78, No. 9, pp. 13061317.
1023
Evidence for Aging Theories from the Study
of a Hunter–Gatherer People (Ache of Paraguay)
G. Libertini
Independent Researcher; Email: giacinto.libertini@tin.it
Received April 25, 2013
Abstract—In the late seventies, a small tribal population of Paraguay, the Ache, living under natural conditions, was studied.
Data from this population turn out to be useful for considerations about evolutionary hypotheses on the aging phenomenon.
1) Ache show an agerelated increasing mortality, which strongly limits the mean duration of life, as observed in other stud
ies on mammal and bird species. 2) According to current theories on aging, in the wild very few or no individual reach old
age and, so, aging cannot be directly influenced by natural selection. However, data from our population show that a signif
icant proportion of the population reaches in the wild 60 and 70 years of age. 3) Data from Ache are also in agreement with
the observation about an inverse correlation between extrinsic mortality and deaths due to the agerelated increasing mor
tality. 4) For many gerontologists, the agerelated decline of vital functions is a consequence of the gradual decline of cell
turnover, genetically determined and regulated by the declining duplication capacities of stem cells. The current interpreta
tion is that these restrictions are a general defense against the proliferation of any tumoral mass. However, among wild Ache
cancer is virtually unknown in nonelderly subjects, and only among older individuals are there deaths attributable to onco
logical diseases. Moreover, fitness decline begins long before oncological diseases have fatal effects in significant numbers.
This completely disproves the current hypothesis, because a supposed defense against a deadly disease cannot exterminate
a population before the disease begins to kill. These data are consistent with similar data from other species studied under
natural conditions, and they bring new arguments against the nonadaptive interpretation of aging and in support of the
adaptive interpretation.
DOI: 10.1134/S0006297913090083
Key words: senescence, evolution, telomere, telomerase, cancer
1024 LIBERTINI
BIOCHEMISTRY (Moscow) Vol. 78 No. 9 2013
unlikely repeatable because hunter–gatherer populations
are disappearing. Figures 13 summarize the life table of
Ache under natural conditions prior to the close and
friendly contact with the modern populations (not friend
ly contacts with “civilized” people were in existence for
many years as indiscriminate killings of Ache as soon as
they were spotted by Paraguayans or, in other cases, their
capture and enslavement). Figure 3 compares the data
obtained from the Ache with those obtained from the
Yanomamo, one of the few other populations studied
under natural conditions.
The data document that, in wild conditions, the
Ache – despite the ruthless killings and captures by
Paraguayans, which caused about one third of the overall
mortality (missing persons included) – had a life table sim
ilar to that of modern populations, with a high and decreas
ing mortality in the first part of life, then a phase in which
the mortality was low and stable, with a minimum at around
1520 years (about 0.9%/year), and finally a third phase in
which the mortality grew slowly at first and then rapidly.
It is noteworthy that, at ages 60 and 70 years, approx
imately 30 and 20%, respectively, of Ache survived.
Fig. 1. a) Probability of death as a function of age; b) life table of Ache people in wild conditions (forest period). Data from Hill and Hurtado
[1].
0.15
0.10
0.05
0
0.20
10 20 30 40 50
Age
Death rate
1.00
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
Survivors, %
60 70 01020304050
60 70
ab
Fig. 2. Comparison of agespecific mortality between the period lived in the forest and during the first contact (a) or during life in the reser
vation (b). Data from Hill and Hurtado [1].
01020304050
Age
Death rate/year
0.20
0.15
0.10
0.05
0.00
60 70 10 20 30 40 50 60 70
ab
0.60
0.50
0.40
0.30
0.20
0.10
Death rate/year
contact
forest
forest
reservation
EVIDENCE FOR AGING FROM A HUNTER–GATHERER PEOPLE 1025
BIOCHEMISTRY (Moscow) Vol. 78 No. 9 2013
Another important fact is that the increased mortal
ity reported for the Ache in wild conditions in the third
phase is not at all indifferent for the overall mean duration
of life (ML).
Figure 4 shows the Ache life table in natural condi
tions and the hypothetical life table that would occur in
the case that there was no agerelated increase of mortal
ity, i.e. in the case in which individuals would not grow
old. In the real life table, the ML is equal to 38.8 years,
while in the hypothetical life table ML is equal to 87.75
years, with a ratio (Ratio 1) between the two values equal
to 2.260. It is worth noting that the length of the abscissas
is extended up to 580 years, since – with a mortality rate
of 0.9%/year, which is about the estimated minimum
mortality in natural conditions – at that age even 0.5% of
the population would survive!
If we consider only the individuals surviving at
the age of 20 years (Fig. 5), the ML of Ache in the wild
was 20 + 38.1 = 58.11 years, while for the hypothetical
curve the ML is 20 + 116.04 = 136.04 years (!), with a
ratio (Ratio 2) between the two values equal to 3.044. In
Fig. 5, the abscissas extend up to 640 years, since at the
age of 634 years about 0.5% of the population would sur
vive!
The hypothetical curves of Figs. 4 and 5, in the sec
tions where the mortality is constant, is calculated using
the simple formula:
Yt= Y0(1 – m0)t, (1)
where Y0– survivors at time 0; Yt– survivors at time t;
m0– minimum mortality; t– time.
Ratio 1 and Ratio 2 may be visualized, in each figure,
as the ratio between the area defined by the hypothetical
curve and the area subtended by the real curve.
Fig. 3. Comparison between the life tables of Ache and
Yanomamo, another hunter–gatherer population. The curves are
essentially overlapping. Data from Hill and Hurtado [1] and Early
and Peters [4].
01020304050
Age
Mortality rate/year
0.20
0.15
0.10
0.05
60 70
Ache
Yanomamo
Fig. 4. Continuous line, life table of Ache in natural conditions (forest period) (data from Hill and Hurtado [1]); dashed line, hypothetical
life table without agerelated increasing mortality.
0 20 40 60 80 100
Years
Survivors
120 140 160
0.9
0.8
0.7
0.6
0.5
0.4
0.3
1.0
0.2
0.1
180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580
1026 LIBERTINI
BIOCHEMISTRY (Moscow) Vol. 78 No. 9 2013
These results, for a human population in wild condi
tions, are consistent with those reported in a previous
work for various species of mammals [5], where the range
of Ratio 1 and Ratio 2 were 1.553.21 and 2.425.09,
respectively (Table 1).
These data show that, for the Ache people in wild
conditions: (i) the increase of mortality is evident at ages
existing in natural conditions; (ii) such mortality increase
strongly reduces the ML; (iii) a substantial part of the
population reaches ages commonly considered as senile.
Since the agerelated increase of mortality, i.e. the
agerelated reduction of fitness alias aging, is clearly pres
ent in natural conditions, it is therefore certainly subject
ed to natural selection. This contradicts a basic assump
tion of the nonadaptive theories of aging (mutation accu
mulation theory [610], antagonistic pleiotropic theory
[11, 12], disposable soma theory [13, 14]), according to
which aging is not subject to natural selection due to the
rarity of elderly individuals under natural conditions: “…
there is scant evidence that senescence contributes signif
icantly to mortality in the wild … As a rule, wild animals
simply do not live long enough to grow old. Therefore,
natural selection has limited opportunity to exert a direct
influence over the process of senescence” [15].
It is good to point out the following. Although the
percentages of Ache who reached the ages of 60 and 70
years are certainly remarkable and perhaps surprising (see
Fig. 1), the key issue is not so much the percentages of
individuals who reach those ages but the percentage of
individuals who, by agerelated fitness reduction, die
before. It is important to avoid the confusion between the
gradual decline of fitness, or aging, and the result of this
process, namely the elderly individuals (see the previous
quotation).
The agerelated fitness decline is clearly a phenome
non subject to natural selection and in need of an evolu
tionary explanation, regardless of the percentage – in
wild conditions – of individuals called “elders” because
Fig. 5. Same as Fig. 4 but only individuals surviving at the age of 20 years are considered.
20 40 60 80 100
Years
Survivors
120 140 160
0.9
0.8
0.7
0.6
0.5
0.4
0.3
1.0
0.2
0.1
0
180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600 620 640
Fig. 6. Inverse relation between extrinsic mortality (m0) and the
proportion of deaths (Ps) due to intrinsic mortality (mi), i.e. the
deaths due to the agerelated increasing mortality. Open rhombs,
mammal species; closed rhombs, bird species; open square, Ache
people in wild conditions. Data are from Ricklefs [16], Table 2 (p.
30). Ricklefs’ Fig. 7 (p. 34) has been redrawn and the datum from
Ache people [1] has been added. Ordinates are in logarithmic
scale.
0.0 0.2 0.4 0.6 0.8
m0
Proportion of deaths due to mi
1.00
0.10
0.01
1.0 1.2
EVIDENCE FOR AGING FROM A HUNTER–GATHERER PEOPLE 1027
BIOCHEMISTRY (Moscow) Vol. 78 No. 9 2013
they have reached a certain threshold of decline, arbitrar
ily defined.
Another important fact is that these results are also in
agreement with Ricklefs’ observation [16] about an
inverse correlation – documented in some mammal and
bird species – between extrinsic mortality (m0) and the
deaths due to the agerelated increasing mortality (Ps), a
relation that disproves nonadaptive aging theories and
supports adaptive aging hypotheses [17], which consider
vertebrate aging a type of phenoptosis, or programmed
death of an individual [18, 19].
With a minimum mortality (m0, approximately
1%/year) and a share of deaths due to senescence (Ps, on
the ordinates) equal to about 67%, the position of the
human species (Ache people) in the graph (Fig. 6) is
highlighted with an open square.
DATA ABOUT DEATH CAUSES IN ACHE PEOPLE
AND THEIR IMPLICATIONS
FOR THE HYPOTHESIS
OF AGERELATED FITNESS DECLINE
AS A DEFENSE AGAINST CANCER
Death causes for Ache people under natural condi
tions (forest period) are shown in Table 2 [1].
It is worth noting that, in Ache people in wild condi
tions, the main causes of death for modern western pop
ulations (heart attacks, diabetes, hypertension, etc.) are
absent. Moreover, cases of death by cancer are not report
ed, although, in the group “adult aged 60+ years”, some
deaths attributed generically to unspecified causes or to
“old age” could be the result of neoplastic diseases. In any
case, the data indicate that neoplastic diseases were rare
events in Ache people in the forest period. This rarity of
cancer in primitive conditions is not a new thing and is
confirmed elsewhere.
For example, some anecdotal, but authoritative,
information about the immunity from cancer of primitive
populations are reported by Price [20]: Dr. J. Romig, “a
surgeon (of Anchorage) of great skill and with an experi
ence among the Eskimos and the Indians, both the prim
itives and the modernized … stated that in his thirtysix
years of contact with these people he had never seen a
case of malignant disease among the truly primitive
Eskimos and Indians, although it frequently occurs when
they become modernized” (p. 83).
Dr. J. R. Nimmo, the government physician in
charge for Torres Strait Islands people told Dr. Price that:
“in his thirteen years with them he had not seen a single
case of malignancy, and seen only one that he had sus
pected might be malignancy among the entire four thou
sand native populations. He stated that during this same
period he had operated on several dozen malignancies for
the white populations, which numbers about three hun
dred” (p. 179).
These data can be used to settle the dispute between
nonadaptive and adaptive interpretations of aging. Non
adaptive theories do not predict at all the existence of
genetically determined and regulated mechanisms that
progressively reduce the fitness. The existence of such
mechanisms would indeed falsify nonadaptive theories,
forcing their total abandonment.
On the contrary, for the plausibility of aging adaptive
theories (e.g. [5]), it is indispensable the existence of
genetically determined and regulated mechanisms for the
agerelated mortality increase [21, 22].
The agerelated decline of vital functions is well
explained as a consequence of the gradual decline of cell
turnover, determined by the declining duplication capac
ities of stem cells by effect of the telomere–telomerase
system [22, 23]. This cell turnover decline is in accor
dance with the adaptive interpretation of aging, while, for
the nonadaptive interpretation, it cannot be accepted as
a mechanism causing senescence and, therefore, a differ
ent rationale is absolutely necessary.
The absence of a valid or at least plausible explana
tion for these mechanisms would indeed disprove all non
adaptive aging theories, transforming them, once and for
all, from potentially valid theories into hypotheses of only
historical value. This would change the validity of a huge
number of works and experiences based on the assump
Species
Zebra
Hippopotamus
Elephant
Waterbuck
Warthog
Impala
Buffalo
Dall mountain sheep
Homo sapiens
(Ache people)
Source
of data
a
c
b
d
a
a
a
e
[1]
Ratio 2
3.20
4.45
2.42
4.02
2.85
3.85
3.46
5.09
3.04
Ratio 1
2.03
2.81
1.67
2.57
1.55
2.64
2.21
3.21
2.26
Table 1. Ratio 1: ratio between ML in natural conditions
and ML in the hypothetical condition that the mortality
rate remains stable at its lowest value for various mammal
species. Ratio 2: the same as Ratio 1 but excluding the
first periods of life, i.e. before mortality reaches its lowest
value. Data from Libertini [5], sources: (a) Spinage,
1972; (b) Laws, 1966; (c) Laws, 1968; (d) Spinage, 1970;
(e) Deevey, 1947, and from Hill and Hurtado [1] (in ital
ics). For all: sexes combined; time unit – year
1028 LIBERTINI
BIOCHEMISTRY (Moscow) Vol. 78 No. 9 2013
1
Violence and accidents
Homicide/neglect
Captured/shot by Paraguayan
Accidents
Total:
Infections/Intoxications
Various causes
Total:
Congenital causes
Unspecified newborn death/defective
Childbirth/Mother had no milk
Total:
Total:
Violence and accidents
Homicide/neglect
Captured/shot by Paraguayan
Accidents
Total:
Infections/Intoxications
Various causes
Total:
Congenital causes
Sick (unspecified)/sick in lungs
Total:
Total:
Violence and accidents
Buried alive
Left behind
Club fight
Homicide, killed by Ache
Shot by Paraguayan
Captured by Paraguayan
Snakebite
Eaten by jaguar
Hit by lightning
Fell from tree/hit by falling tree
Lost
Total:
Infections/Intoxications
Fever after eating pichu larvae
Fever after eating kracho larvae
Fever after eating honey
Fever after eating palm starch/corn
Malaria
Fever after touching blood
Skin infection/sores on neck
Swollen body/systemic infection
Total:
Table 2. Causes of death for Ache people in natural conditions (forest period) (data from Hill and Hurtado [1])
3
58.02%
27.48%
14.50%
100%
84.85%
11.11%
4.04%
100%
69.05%
24.60%
2
52
21
3
76
36
36
17
2
19
131
17
56
11
84
11
11
4
4
99
1
1
6
3
46
1
15
8
3
2
1
87
8
5
6
2
2
3
2
3
31
In children aged 03 years
In children aged 414 years
In adults aged 1559 years
EVIDENCE FOR AGING FROM A HUNTER–GATHERER PEOPLE 1029
BIOCHEMISTRY (Moscow) Vol. 78 No. 9 2013
tion of aging as a nonadaptive phenomenon. Some of the
best researchers have therefore sought a plausible justifi
cation for the abovementioned mechanisms different
from that which explains them purely and simply as
determinants of aging.
The current authoritative justification, in fact the
only hypothesis widespread and supported in the scientif
ic world, is that these restrictions are a general defense
against cancer, because they would limit the pathological
proliferation of any tumoral mass [2426].
If we compare the agerelated increasing mortality in
natural conditions (Ache population; Fig. 7a) with the
incidence of cancer and the deaths caused by it in a mod
ern population (Great Britain; Fig. 7b), at first sight this
explanation could seem plausible.
The appearance is misleading and data presented in
such a way lead to a false confirmation of current opinion.
It is necessary to draw, on a single graph and using a sin
gle scale, the rates of: a) total mortality for Ache under
natural conditions; b) plausible cancer death rates in wild
Aches; and, by comparison: c) cancer death rates in the
modern population (Fig. 8). It is evident that, in the wild,
the increase in overall mortality (over the minimum value
of about 1%) anticipates and is much higher than the
mortality from cancer both in the wild and in the modern
population. Moreover, under natural conditions, when
there are the first possible cases of deaths by cancer, fit
ness decline has already determined the death of most
individuals.
This completely disproves the hypothesis that the
reduction of cell duplication capacities would be a
defense against cancer: it would be like arguing that a
defense against a deadly disease has the effect of mass
killing before the disease begins to kill! On the contrary,
according to the adaptive hypothesis of aging, the decline
of defense against cancer results also from the decline of
cell replication capacities and the cases of cancer in old
age are part of aging characteristics [22].
1
Other causes
Childbirth
Stomach problems
Liver problems
Sick in lungs
Sick (unspecified)
Old age
Total:
Total:
Violence and accidents
Buried
Left behind
Club fight
Shot by Paraguayan
Eaten by jaguar
Snakebite
Lost
Total:
Other causes
Diarrhea
Sick (unspecified)
Old age
Total:
Total:
Age 03 years
Age 414 years
Age 1559 years
Age 60+ years
Total:
Table 2 (Contd.)
3
6.35%
100%
59.26%
40.74%
100%
34.20%
25.85%
32.90%
7.05%
100%
2
3
1
1
1
1
1
8
126
1
2
2
4
1
3
3
16
3
2
6
11
27
131
99
126
27
383
In adults aged 60+ years
Overall number of deaths
1030 LIBERTINI
BIOCHEMISTRY (Moscow) Vol. 78 No. 9 2013
Fig. 7. a) Life table of Ache people in natural conditions (forest period); data from Hill and Hurtado [1]; b) incidence of cancer and cancer
deaths in a modern western population (UK) [2729].
0 5 10 15 20
Death rates/year
0.20
0.18
0.16
25 30
04
Age at death
59
1014
1519
2024
2529
3034
3539
4044
4549
5054
5559
6064
6569
7074
7579
8084
85+
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
Males
Females
Mean
35 40 45 50 55 60 65 70 75
Years
Deaths/year
20 000
15 000
10 000
5000
0
Death rate/100 000
3200
2400
1600
800
0
a
b
EVIDENCE FOR AGING FROM A HUNTER–GATHERER PEOPLE 1031
BIOCHEMISTRY (Moscow) Vol. 78 No. 9 2013
CONCLUSION
For aging research, the observation of a species
under natural conditions is essential because it allows the
evaluation of the phenomenon in the real conditions in
which natural selection acts. This enables the avoidance
of possible misconceptions on which any theoretical con
struction would be fallacious and the verification of
whether, in natural conditions, some theoretical predic
tions are confirmed or falsified.
The study of the human species under natural condi
tions should give, and gives, results similar to those
obtained from studies of other vertebrate species.
1) According to current nonadaptive interpretation
of aging, very few or no individual reach old age and, so,
aging cannot be directly influenced by natural selection
[15]. However, data from a human population in the wild
show that a significant proportion of the population
reaches 60 and 70 years of age (about 30 and 20%, respec
tively). Moreover, if we consider not the illdefined con
cepts of “aging” and “old age” but the agerelated mor
tality increase, a perfectly definable parameter, this phe
nomenon greatly reduces the mean duration of life (67%
in Ache people in wild conditions!) and, therefore, it is
absurd to consider this increase in mortality as something
that is not influenced by natural selection or of no impor
tance for selective process.
These data are consistent with similar data from
other vertebrate species studied under natural conditions
[16] and invalidate the main theoretical tenet of current
evolutionary hypotheses about aging.
2) Nonadaptive aging theories predict a direct relation
between the deaths due to the agerelated increasing mortal
ity and extrinsic mortality [15] while adaptive aging theories
predict an inverse relation [5, 17]. Ricklefs’ data on some
mammal and bird species [16] confirm the prediction of the
adaptive aging hypothesis and falsify the opposite thesis. The
Ache life table is perfectly consistent with Ricklefs’ data.
3) Nonadaptive aging theories offer no valid expla
nation about the known limitations in cell replication and
cell turnover that are the most plausible interpretation of
agerelated fitness decline.
The supporters of nonadaptive theories of aging, in
the attempt to formulate a plausible explanation, hypoth
esize that these limits are a general defense against cancer.
However, data from a population in natural conditions,
and even from modern populations where cancer inci
dence is greatly increased, show that deaths from cancer
are chronologically subsequent to the agerelated
increase in mortality and have a frequency much lower
than the deaths caused by this increase in mortality. This
shows that from a logical point of view the hypothesis that
the aforesaid limits are a general defense against cancer is
untenable.
Fig. 8. Total mortality and plausible cancer death rates for Ache under natural conditions and cancer death rates in a modern population
(Great Britain).
2024 2529 3034
Ages
Death rates/year
3539 4044
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.16
0.00 4549 5054 5559 6064 6569 7074 7579
Cancer death rates in UK
Overall death rates in wild Ache
Plausible cancer death rates in wild Ache
1032 LIBERTINI
BIOCHEMISTRY (Moscow) Vol. 78 No. 9 2013
In short, the study of a human population under nat
ural conditions brings new arguments against the non
adaptive interpretation of aging. This hypothesis (actual
ly, a group of illdefined theories) is commonly presented
as the true and only scientific explanation of aging, but,
when a hypothesis is widely and repeatedly disproved by
empirical data, the scientific method requires that it must
be considered as no longer scientifically acceptable and
confined within the hypotheses of historical interest.
The blowgun of the humble Ache has a poison that
turns out to be fatal to old and widespread beliefs.
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