1990 Test of socioeconomic causation of secular trend

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AMERICAN JOURNAL
OF
PHYSICAL ANTHROPOLOGY
83:459-465
(1990)
Test of Socioeconomic Causation
of
Secular Trend:
Stature Changes Among Favored and Oppressed
South Africans Are Parallel
M.
HENNEBERG
AND
E.R.
VLV
DEN
BERG
Department
of
Anatomy and Cell Biolog
,
University
of
Cape Town
Medical School, Observatory
7925,
Soud
Africa
KEY
WORDS
Growth, Ecosensitivity, Selection
ABSTRACT
Secular trends in body height, however common, run at
different rates and even in opposite directions in various populations. The
standard explanation is that direction and tempo
of
the trend are reflections
of
changes in the socioeconomic situation. The aim
of
this work is to test this
hypothesis by examining trends in different socioeconomic groups living in the
same country.
Our observations on affluent South Africans
of
European extraction (AE)
and on Polish medical students are compared with the data on statures
of
other
affluent and poor peoples from the
two
countries measured at various dates
during the 19th and 20th centuries. The trend among native Southern
Africans is erratic (Tobias:
South
African Journal of Medical Science
40:145-
164,1975), but the overall direction is positive with
a
slow rate (0.24 cddecade
for
72 Negroid male groups and
0.48
cdd
for
28 Khoisan male samples).
Magnitude of the trend among adult
AE
(0.41 cdd
for
females, 0.59 for males)
does not differ significantly from that among natives. The trend was absent, in
the data for 10-year-old
AE
boys and girls. The rate
of
trend among
AE
is much
lower than that in their countries
of
origin (mainly Holland and Britain). The
trend among
AE
medical students
is
markedly weaker than the trend among
Polish medical students
(1.21
cdd), who in turn parallel Polish general
conscripts (1.24 cdd). It follows that the explanation
of
the secular trend as
being an ecosensitive response
of
individuals to changing levels
of
well-being
is
insufficient.
The human species is continuously un-
dergoing a number of microevolutionary
changes. Whether these are adaptive in
character or due
to
random forces is debat-
able. It is also uncertain whether some are
true microevolutionary phenomena due to
changing fre uencies of alleles in the gene
pools
or
whet
x
er they are only ecosensitive
responses of individuals
to
changing living
conditions. It is es ecially true with respect
to morphological c aracters that are deter-
mined by both heredity and environment.
The classic case in point is the secular trend
in stature during recent decades.
The directions and rates
of
stature change
through time in various populations are far
from uniform (Tobias and Netscher, 1977;
Wolanski, 1978; Cameron, 1979; Roche,
1979; Tobias, 1985; Van Wieringen, 1986,
Price et al., 1987). Although the most com-
mon view is that the trend occurs as an
ecosensitive change in response to variations
in living conditions without alteration
of
gene
pools,
other causes such as heterosis
(Wolanski, 1978) and even natural selection
(Chiarelli, 1977), have been postulated.
Change in gene pools, due probably to natu-
Received
August
15,1989; accepted May 16,1990.
M. Henneberg is now at Department
of
Anatomy and Human
Biology, University
of
the Witwatersrand Medical School, Park-
town 2193, Johannesburg, South Africa.
0
1990 WILEY-LISS,
INC.

460
M.
HENNEBERG
AND
E.R.
VAN
DEN
BERG
ral selection, was suggested to be responsible
for other trends, such as reduction in tooth
size (Calcagno and Gibson, 19881, brachy-
cephalization (Bielicki and Welon, 1964;
Henneberg, 19761, and decrease in cranial
capacity (Henneberg, 1988). Thus it may be
postulated that there is a lack of clarity as to
the causes
of
the secular change in stature.
This lack of clarity results partly from the
way in which hypotheses were tested. Often
observational data are presented without
explicit formulation
of
a
testable hypothesis,
only with a tentative interpretation based on
canaideration
of
a
hited body
of
coincident
facts.
The most common explanation in the liter-
ature on secular trends is that direction and
tempo of the trend are reflections
of
changes
in the socioeconomic situation. This explana-
tion is based on a simple coincidence be-
tween stature increase in
a
given nation and
this nation’s improving socioeconomic condi-
tions. Less attention was paid
to
compari-
sons
of
trends in different socioeconomic
subpopulations
of
the same nation. Such
comparisons offer an opportunity to test the
hypothesis tying secular change to socioeco-
nomic change. The aim of this paper is to
present this test.
According
to
the “environmental hypothe-
sis,’ any trend due exclusively to an ecosensi-
tive response of a growing body
to
change in
socioeconomic situation should meet two
conditions:
1)
direction and the magnitude of
changes should be similar under comparable
socioeconomic circumstances in various pop-
ulations, and 2) direction andor magnitude
of
the trend in sectors
of
the same nation
showing different dynamics
of
socioeconomic
change should differ accordingly.
Southern Africa, with its stark contrasts
in opportunities
for
socioeconomic advance-
ment between various sectors
of
the popula-
tion, offers a good opportunity to test the
environmental hypothesis. Some informa-
tion useful in further testing
of
the hypothe-
sis can be extracted from the vast body
of
the
literature pertaining
to
the secular trend in
stature in Europe and America. This will be
used in the discussion.
THE SOUTHERN AFRICAN CASE
Material
This case study is based on the material
derived from three sources:
1)
skeletons
of
41
adult males and 45 adult females born be-
tween the years 1803 and 1922 buried at the “whit‘k“ ad “black peoples is
too
simplistic
“white” upper-class cemetery in Wynberg,
Cape Town (van den Berg 1990), 2) anthro-
pometric measurements
of
the “white” first-
year medical students at the University
of
Ca e Town durin 1988 and 1989
(86
males,
63 females), and
3
5
literature (see tables and
Discussion
for
descriptions and quotations).
Ethnic and “racial” nomenclature in
Southern Africa
is
confusing since various
names and classifications became misused
for political reasons and have strong emo-
tianal connotations. Throughout this paper
we shall use the following terms that we feel
shodd
be
perceived
as
Qhjective and
no%-
offensive: African
of
European extraction
(N3k-a
member
of
a
population whose an-
cestors came mainly from Holland and En-
gland (beginning in 1652) but who contains
substantial admixtures of Portugese, Jews,
French, Central Europeans, and Eastern
Europeans as well as some native peoples.
They are colloquially referred to as “white.’,
Members
of
this group were favored by the
local laws over the last three centuries. Their
socioeconomic development proceeded in
ways similar
to
those in areas of successful
European colonization (America, Australia).
Negroids-native people
of
Africa who are
said to have arrived in the Southern part
of
the continent only a few thousand years ago.
Most
of
them speak languages imprecisely
classified by Europeans as “Bantu.” These
agriculturists and pastoralists were frus-
trated in their traditional advancement
as
well as in the Western-style urbanization by
European colonization
of
their territories
and by oppressive legislation. Many tribes
differed between themselves socioeconomi-
cally and were at various times treated dif-
ferently by invading
AE.
Khoisan-native
people
of
the Southern African subcontinent
who are said
to
have lived in the area for
many thousands
of
years. Their morphology
is unlike that
of
Negroids and they speak
a
distinctive group of languages containing
“clicks.” Traditionally hunter-gatherers
or
pastoralists, the Khoisan were, in some ar-
eas, situated below Negroids in the socioeco-
nomic hierarchy. Some Khoisan groups pur-
sued their traditional lifestyle well into the
20th century. Like Negroids, they were de-
nied political rights and had only
a
very
limited opportunity
for
economic advance-
ment. In this paper a collective term,
“natives,” will be sometimes used to describe
iointlv Nemroids and Khoisan. The cliche
of

SOCIOECONOMIC CAUSATION
46
1
TABLE
1.
Body height of young
(18+
years old) South African adult males of European extraction
Year examined Height (mm) Group Author
1877l
1935
1935
1966
1966
1973
l94P
1,722
1,729
1,736
1,775
1,773
1,745
Wynberg Cemetery
Cape Province Brown
(1935)
Secondary Schools
Special Service Cluver
(1935)
soldiers, Pretoria
Bloemfontein,
OFS
Grobbelaar
(1967)
Secondary schools
Univ.
of
Cape Town
students, Med. Sch.
Johannesburg, Richardson
(1978)
Secondarv Schools
van den Berg
(1990)
Sloan
(1967)
1
79.1
IJniv of Cape Town Own data
students, Med. Sch.
‘Average date
of
birth
plus
20
years.
TABLE
2.
Body height
of
young South African adult females of European extraction
Year examined Height (mm) Group Author
1880’
1935
1966
1978
1986
1988
1,609
Wynberg Cemetery van den Berg
(1990)
1,618
Cape Province Brown
(1935)
Secondary Schools
1,646
Bloemfontein,
OFS
Grobbelaar
(1967)
Secondary Schools
1,625
Johannesburg Richardson
(1978)
Secondary Schools
1,660
Bloemfontein
OFS
Gouws and van der
students Merwe
(1987)
1,649
Univ.
of
Cape Town Own data
students. Med. Sch.
‘Average
year
of
birth
plus
20
years
to
be applied
to
the complex situation
of
the
subcontinent. For instance, “black in cer-
tain situations will include immigrants from
India, South-East Asia, and “coloured peo-
ple
of
mixed origin.
Body height in the skeletal sample was
reconstructed from all the long bones of each
skeleton preserved well enough to warrant
measurement. A number
of
appropriate for-
mulae (Krogman and Isgan, 1986) were used
in each case and results averaged. Medical
students were measured with the use of a
GPM anthropometer
to
the nearest millime-
ter during special anthropometry practi-
cals.’ These
AE
data were supplemented by
statures of medical students and other
young
AE
adults measured earlier and re-
ported in the literature (Tables
1,
2).
To
address the question
of
growth acceleration,
‘Thanks are
due
to Prof.
A.G.
Morris for permission to
use
this
material.
data on 10 year-old
AE
boys and
girls
were
also taken from the literature (Table 3). Data
on body heights
of
adult native males were
all taken from
a
compilation
by
Tobias
(19751, who tabulated averages
for
some 93
Negroid groups and
for
28
groups
of
Khoisan
peoples.
All
averages listed in the Tobias
tables were used, with the exception
of
22
groups
of
Malawians measured by
G.
Nurse
in 1969. Only the grand total
for
these
groups was used. The reason was not
to
bias
the data by entering
so
many separate aver-
ages
for
geographically close peoples mea-
sured in the same year. There is such a
scarcity
of
data
for
native adult females
(Eveleth and Tanner, 1976) that no analysis
has been attempted.
Methods
Averages
for
all groups were treated as
individual points in regression analyses run
separately
for
adult
AE
males, adult
AE
females,
AE
boys,
AE
girls, Negroid South-

462
M.
HENNEBERG
AND
E.R.
VAN
DEN
BERG
ern Africans, and Khoisan peo le. Body
tion, assuming
for
the skeletal material the
year of examination
to
be 20 years after the
average birthdate. Linearity of regression
was tested by comparing goodness-of-fit of
straight lines and an array
of
various curvi-
linear models applied to the data. Regression
slopes and correlation coefficients were de-
termined and their significance was evalu-
ated by means
of
t-tests. The significance of
differences between slopes of regression
lines and between correlation coefficients
tervals.
A
conventional significance level
of
0.05
was used throughout unless otherwise
indicated.
Results
The average heights of affluent adult
AE
(Tables 1,2) indicate a positive secular trend
over the last
11
decades. The magnitude of
this trend, however, is small. The trends do
not deviate significantly from straight lines.
Slopes of regression lines (Table
4)
allow
evaluation of the overall tempo of change
height was regressed on the year
o
fp
examina-
xgas
decn,.";n*
Illllld
by
means
sf
cmfidence
in-
better than do individual data point compar-
isons. In both males and females, increase in
body height was approximately
0.5
cm per
decade. No significant increase was found in
statures of
10
year-old
AE
children. Slopes of
respective regression lines, taken at their
face value, indicate little change (Table 4).
The trend among Negroid adult males is
linear, significant, and positive. The numer-
ical value of the slope indicates a tempo
slower than that among adult
AE,
but the
difference between Negroid and
AE
slopes
is
not significant. The trend among Khoisan
males
is
similar
to
that
fwnd
among-AE.
The
confidence intervals of Khoisan, Negroid,
and
AE
slo
es overlap each other consider-
not differ significantly.
ably; thus
t
K
e tempos of the three trends do
DISCUSSION
Relative scarcity of Southern African data
and their heterogeneity demand caution in
the interpretation of results. The fact that
Tobias
(1975)
after simple inspection of tab-
ulated averages interprets the same data for
Negroid males as indicating no positive sec-
TABLE
3.
Body height of South African
10
year-old boys and girls of European extraction
Body height
Year Boys Girls Area Author
1935
1945
1958
1963
1966
1985
1986
1978
1,356 1,356
1,372 1,361
1,378 1,416
1,416 1,424
1.391 1.409
i,3ii
1,309
1,399 1,398
__
1,434
Cape Province
South Africa
Cape Town
Pretoria
Bioemfclntein
Jonannesburg
South Africa
Bloemfontein,
OFS
Brown
(1935)
Cluver et
al.
(1946)
Lurie
(1958)
Smit and Potgieter
(19671
Grobbelaar
(1967)
Richarason
(197a)
Kotze et al.
(1986)
Gouws and van der Merwe
(1987)
TABLE
4.
Correlation coefficients and slopes of linear regressions of body height on the year of examination for
Southern African groups'
Limits of
95%
N confidence interv. Signif.
of
Data set (groups) r Slope Lower Upper slope
P
European adult males
7 0.81 0.59 0.09 1.09 0.03
European adult females
6 0.83 0.41 0.04 0.78 0.04
European
10
year-old boys
7 0.01 0.10
-
2.14 2.34 (0.91)
ins
European
10
year-old girls
8
0.25 0.59
-
1.65 2.83 (0.54)
ins
"Negroid" adult males2
72 0.24 0.24 0.01 0.47 0.04
Khoi-San adult males"
28 0.54 0.48 0.17 0.79 0.003
Polish adult males'
7 0.95 1.14 0.90 1.92 0.0009
'Data for better-off Polish males (Table
5)
are included
for
comparison.
'Data from Tobias
(1975).

SOCIOECONOMIC CAUSATION
463
ular trend, whereas our regression analysis
shows a significant positive, albeit small
trend, is a case in point. Irrespective
of
these
difficulties it may be concluded that in
Southern Africa the direction and the mag-
nitude
of
trends in groups
of
various origin
are similar, despite substantial socioeco-
nomic differences.
Secular trends in stature among adults in
Southern Africa, be they Negroid, Khoisan,
or
AE,
seem weak
or
barely noticeable when
contrasted with those found in some coun-
tries
of
the northern hemisphere where
tem-
pos often exceeded
1
cddecade (e.g., Proko-
pec, 1984; Stinson, 1985; van Wieringen,
1986).
One of the possible ex lanations
of
the
AE
is that suggested by Tobias (1985), who
postulated that “have-most” people show ab-
sence
of
the positive trend since they have
already reached the upper phenotypic limit
weakness
of
trends in bot
r:
the natives and
1200
{
L
_____
/___?_.
-
-__
-
--
1880
1900
1920
1940 1960
1980
2000
yr
Fi
1
The secular trend of body height among afflu-
ent gouth Africans
of
European extraction.
M
=
adult
males; F
=
adult females;
b
=
10
year-old boys; g
=
10
year-old girls; N
=
“Negroid Southern African males;
D
=
Dutch conscripts (van Wieringen,
1986)
added for
comparison.
set by their genetic endowment, while the
absence
of
the positive trend among “have-
little” peoples, who are still depressed, is due
to the fact that no improvement occurs in
their living conditions. Adult
AE
males are
indeed several centimeters taller than their
Negroid counterparts (Fig. 1). If this “envi-
ronmental” explanation
of
secular trends
were true one would predict that in countries
where peoples
of
lower socioeconomic stand-
ing were given an opportunity to improve
their situation at the expense of higher
“classes” the trend among them should be
faster than among previously better-off
a~g-
ments
of
the nation.
The above prediction can be tested by us-
ing Polish male data. Polish medical stu-
dents in 1930’s and in the 1980’s were com-
ing from a similar socioeconomic stratum
of
the society, despite post-war efforts
at
erad-
icaton
of
socioeconomic status differences.
According
to
our analysis (Henneberg et al.,
1985) 64%
of
students had parents with full
university education, similar
to
the 1930’s.
Thus the socioeconomic situation of students
could have only worsened,
or
at least did not
improve much, due
to
the social and eco-
nomic policies in post-war Poland disadvan-
taging educated people. These policies
caused economic advancement
of
poorer sec-
tors
of
the society. Thus body heights
of
all
conscripts in the country, where approxi-
mately
5%
of
people had university educa-
tion, should increase faster than those of
medical students. Polish students coming
from hi her socioeconomic-status groups
conscript both in the first and in the second
half
of
the 20th century (Table
5).
The rate
of
the secular trend in stature
of
students,
however, between 1930 and 1983 was 1.21
cddecade, i.e., virtually identical
to
that
among conscripts (1925-1976: 1.24
cd
decade).
were
in
B
eed taller than an average Polish
TABLE
5.
Body heights of Polish better-off young adult males’
Year Height
(mm)
Group Author
1885 1,650 Selected conscripts Piontek (1971)
1915 1,655 Selected conscripts Piontek (1971)
1925 1,669 Conscripts Piontek (1971)
1930 1,706 Medical students Wrzosek (1931)
1957 1,734 Medical students Malinowski and Strzalko (1970)
1967 1,760 Mecical students Malinowski and Strzalko (1970)
1983 1,770 Medical students Henneberg et al. (1985)
’Note that the average for the national sample of Polish conscripts in
1976
was
1732.1
mm (Bielicki and
Welon
1982)

464
M.
HENNEBERG
AND
E.R.
VAN
DEN
BERG
In a similar vein, but
for
somewhat differ-
ent socioeconomic reasons, one would expect
the rate
of
the secular trend among Harvard
students to be less than in the general
US
population. Data quoted by Stinson (1983,
however, indicate the opposite: the rate
for
Harvard students was 0.98 cddecade (1930-
1959) while the general
US
rate was 0.31
cddecade in the same period. Our findings
also seem to be supported by the general
conclusion
of
van Wieringen (1986) that “the
whole spectrum
of
adult height is still in-
creasing” in Holland; and by parallelism
of
the trend among Czechosiovakian urban in-
telligentsia and industrial and rural workers
(Prokopec, 1984). These observations, cou-
pled with the fact that the secular trend in
stature was still going strong in the 1970’s in
some economically advanced groups or na-
tions while it had halted in others (Roche,
19791, seem to indicate the operation
of
more
specific factors than just the change in socio-
economic conditions. Thus, the “environ-
mental hypothesis” may be falsified.
We are in no position at present
to
advance
a
fully constructed alternate hypothesis.
Some possibilities, however, should be indi-
cated. Heritability
of
body height is consider-
able: 56%
to
99%
of
variance in stature is
of
genetic origin (Cavalli-Sforza and Bodmer,
1971; Mueller, 1976; Roberts et al., 1978).
Attempts at estimating the influence
of
en-
vironmental factors (Bielicki et al., 1981,
Jedlinska, 1985) indicate that no more than
a quarter, but usually less than
lo%,
of
the
variance in stature can be explained by vari-
ability
of
such combined socioeconomic
fac-
tors as education and occupation
of
parents,
type
of
residence (urbadrural, big cityhmall
town), and number
of
children in the family.
Stature is then largely heritable. The differ-
ences in average stature observed between
members
of
the most socioeconomically con-
trasting segments
of
ethnically relatively
homogeneous nations do not exceed
1
stan-
dard deviation, that is, usually close
to
6-7
cm (e.g., 6.5 cm in Poland [Bielicki and
Welon, 19821,2-3 cm in Britain [Rosenbaum
et al., 19851). At the same time, however, the
secular trend may have shifted the average
body height by as much
as
15 cm (Holland;
van Wieringen, 1986)
or
12 cm (Poland-
Table
5).
Even in our
AE
material, with the
slow tempo
of
the trend, the change
is
7.1 cm
in adult males and
5.1
cm in adult females.
The change caused by the trend is too big to
be explained entirely by the ecosensitive re-
sponse to improvement in socioeconomic sit-
uation. Therefore alteration
of
the genetic
endowement is suggested.
As a cause
of
such genetic background
for
the secular trend a change in mating prac-
tices leading to heterosis (Wolanski, 1978)
seems
to
be unlikely since the trend is well
pronounced in countries where there were no
genetic isolates and no significant breakup
of
such isolates occurred during last two
centuries (e.g., Poland, Czechoslovakia, Hol-
land). These countries had low coefficients
of
inbreeding already in the
19th
century (Hen-
neberg,
1979)
before most
of
the trend took
place. Our
AE
peoples were mixing consider-
ably with migrants from all over Europe, and
to
some extent with native people, thus in-
creasing their heterozygosity, but the trend
among them was slow.
It seems rather that some selective mech-
anism could be at work. This is very likely
with respect
to
long-term changes in stature
since the Upper Paleolithic (Frayer, 1984;
Henneberg, 1988). The general relaxation
of
selection in economically advanced nations
makes it difficult
to
postulate
a
direct adap-
tive significance
of
body size that can be used
as
an explanation
for
prehistoric trends.
Thus it seems more plausible
to
postulate
a
relationship between genetic susceptibility
to
some pathogenic factors and the regula-
tion
of
growth.
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