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 examiningtrends in different socioeconomicgroups 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 40:145164,1975),but the overall directionis positive with a slow rate (0.24cddecade for 72 Negroid male groups and 0.48 c d d for 28 Khoisan male samples). Magnitude of the trend among adult AE (0.41c d d for females, 0.59 for males) does not differ significantlyfrom that among natives. The trend was absent,in the data for 10-year-oldAE boys and girls. The rate of trend among AE is much lower than that in their countries of origin (mainlyHolland 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 c d d ) . It follows that the explanation of the secular trend as being an ecosensitive response of individuals to changing levels of well-beingis insufficient.
The human species is continuously undergoing a number of microevolutionary changes. Whether these are adaptive in character or due to random forces is debatable. It is also uncertain whether some are true microevolutionary phenomena due to changing fre uencies of alleles in the gene pools or whet 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 determined 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
x
0 1990 WILEY-LISS, INC.
from uniform (Tobias and Netscher, 1977; Wolanski, 1978; Cameron, 1979; Roche, 1979; Tobias, 1985; Van Wieringen, 1986, Price et al., 1987). Although the most common view is that the trend occurs as an ecosensitivechange 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 natuReceived August 15,1989; accepted May 16,1990. M. Henneberg is now a t Department of Anatomy and Human Biology, University of the Witwatersrand Medical School, Parktown 2193, Johannesburg, South Africa.
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, brachycephalization (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 h i t e d body of coincident facts. The most common explanation in the literature on secular trends is that direction and tempo of the trend are reflections of changes in the socioeconomicsituation. This explanation is based on a simple coincidence between stature increase in a given nation and this nation’s improving socioeconomicconditions. Less attention was paid to comparisons of trends in different socioeconomic subpopulations of the same nation. Such comparisons offer an opportunity to test the hypothesis tying secular change to socioeconomic change. The aim of this paper is to present this test. According to the “environmental hypothesis,’any trend due exclusivelyto an ecosensitive 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 socioeconomiccircumstances in various populations, and 2) direction andor magnitude of the trend in sectors of the same nation showingdifferent dynamics of socioeconomic change should differ accordingly. Southern Africa, with its stark contrasts in opportunities for socioeconomic advancement between various sectors of the population, offers a good opportunity to test the environmental hypothesis. Some information useful in further testing of the hypothesis 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)skeletonsof 41 adult males and 45 adult females born between the years 1803and 1922 buried at the
“white” upper-class cemetery in Wynberg, Cape Town (van den Berg 1990), 2) anthropometric measurements of the “white”firstyear medical students at the University of Ca e Town durin 1988 and 1989 (86 males, 63females), and 3 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 emotianal connotations. Throughout this paper we shall use the following terms that we feel shodd be perceived as Qhjectiveand no%offensive: African of European extraction (N3k-a member of a population whose ancestors came mainly from Holland and England (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 frustrated in their traditional advancement as well as in the Western-styleurbanization by European colonization of their territories and by oppressive legislation. Many tribes differed between themselves socioeconomically and were at various times treated differently 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 areas, situated below Negroids in the socioeconomic hierarchy. Some Khoisan groups pursued their traditional lifestyle well into the 20th century. Like Negroids, they were denied political rights and had only a very limited opportunity for economic advancement. In this paper a collective term, “natives,”will be sometimes used to describe iointlv Nemroids and Khoisan. The cliche of “whit‘k“a d “black peoples is too simplistic
5
46 1
SOCIOECONOMIC CAUSATION TABLE 1 . Body height of young (18+ years old) South African adult males of European extraction Year examined
Height (mm)
Group
Author
1877l 1935
1,722 1,729
v a n den Berg (1990) Brown (1935)
1935
1,736
1966
1,775
1966
1,773
1973
1,745
l94P
1 79.1
Wynberg Cemetery Cape Province Secondary Schools Special Service soldiers, Pretoria Bloemfontein, OFS Secondary schools Univ. of Cape Town students, Med. Sch. Johannesburg, Secondarv Schools IJniv of Cape Town students, Med. Sch.
Cluver (1935) Grobbelaar (1967) Sloan (1967) Richardson (1978) Own d a t a
‘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
1,609 1,618
van den Berg (1990) Brown (1935)
1966
1,646
1978
1,625
1986
1,660
1988
1,649
Wynberg Cemetery Cape Province Secondary Schools Bloemfontein, OFS Secondary Schools Johannesburg Secondary Schools Bloemfontein OFS students Univ. of Cape Town students. Med. Sch.
Grobbelaar (1967) Richardson (1978) Gouws and van der Merwe (1987) Own data
‘Average year of birth plus 20 years
to be applied to the complex situation of the subcontinent. For instance, “black in certain situations will include immigrants from India, South-East Asia, and “coloured people 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 formulae (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 millimeter during special anthropometry practicals.’ These AE data were supplemented by statures of medical students and other young AE adults measured earlier and reported 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 averages for geographically close peoples measured 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 better than do individual data point comparheight was regressed on the year ofpexamina- isons. In both males and females, increase in tion, assuming for the skeletal material the body height was approximately 0.5 cm per year of examination to be 20 years after the decade. No significant increase was found in average birthdate. Linearity of regression statures of 10year-old AE children. Slopes of was tested by comparing goodness-of-fit of respective regression lines, taken at their straight lines and an array of various curvi- face value, indicate little change (Table 4). linear models applied to the data. Regression The trend among Negroid adult males is slopes and correlation coefficients were de- linear, significant, and positive. The numertermined and their significance was evalu- ical value of the slope indicates a tempo ated by means of t-tests. The significance of slower than that among adult AE, but the differences between slopes of regression difference between Negroid and AE slopes is lines and between correlation coefficients not significant. The trend among Khoisan xgas decn,.";n* Illllld by means sf cmfidence in- males is similar to that fwnd among-AE.The tervals. A conventional significance level of confidence intervals of Khoisan, Negroid, 0.05 was used throughout unless otherwise and AE slo es overlap each other considerindicated. ably; thus t e tempos of the three trends do not differ significantly.
K
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
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 tabulated 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 1978 1985 1986
1,356 1,372 1,378 1,416 1.391
1,356 1,361 1,416 1,424 1.409 1,309 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)
i,3ii
1,399 __
TABLE 4. Correlation coefficients and slopes of linear regressions of body height on the year of examination for Southern African groups'
Data set European adult males European adult females European 10 year-old boys European 10 year-old girls "Negroid" adult males2 Khoi-San adult males" Polish adult males'
N (groups)
r
Slope
7 6 7 8 72 28 7
0.81 0.83 0.01 0.25 0.24 0.54 0.95
0.59 0.41 0.10 0.59 0.24 0.48 1.14
'Data for better-off Polish males (Table 5) are included for comparison. 'Data from Tobias (1975).
Limits of 95% confidence interv. Lower Upper
Signif. o f slope P
0.09 0.04 - 2.14 - 1.65 0.01 0.17 0.90
0.03 0.04 (0.91) ins (0.54) ins 0.04 0.003 0.0009
1.09 0.78 2.34 2.83 0.47 0.79 1.92
463
SOCIOECONOMIC CAUSATION
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 magnitude of trends in groups of various origin are similar, despite substantial socioeconomic 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 countries of the northern hemisphere where tempos often exceeded 1cddecade (e.g., Prokopec, 1984; Stinson, 1985; van Wieringen, 1986). One of the possible ex lanations of the weakness of trends in bot the natives and AE is that suggested by Tobias (1985),who postulated that “have-most”people show absence of the positive trend since they have already reached the upper phenotypic limit
r:
1200
{ L
_____ 1880
-
/___?_.
1900
1920
1940
-__ 1960
B
--
1980
set by their genetic endowment, while the absence of the positive trend among “havelittle” 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 “environmental” explanation of secular trends were true one would predict that in countries where peoples of lower socioeconomicstanding 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 using Polish male data. Polish medical students in 1930’s and in the 1980’s were coming from a similar socioeconomicstratum of the society, despite post-war efforts at eradicaton 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 socioeconomicsituation of students could have only worsened, or at least did not improve much, due to the social and economic policies in post-war Poland disadvantaging educated people. These policies caused economic advancement of poorer sectors of the society. Thus body heights of all conscripts in the country, where approximately 5% of people had university education, should increase faster than those of medical students. Polish students coming from hi her socioeconomic-status groups were in eed taller than an average Polish 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 c d decade).
2000
yr
Fi 1 The secular trend of body height among affluent 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.
TABLE 5. Body heights of Polish better-off young adult males’ Year
Height (mm)
Group
Author
1885 1915 1925 1930 1957 1967 1983
1,650 1,655 1,669 1,706 1,734 1,760 1,770
Selected conscripts Selected conscripts Conscripts Medical students Medical students Mecical students Medical students
Piontek (1971) Piontek (1971) Piontek (1971) Wrzosek (1931) Malinowski and Strzalko (1970) Malinowski and Strzalko (1970) 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 different socioeconomicreasons, 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 (19301959) 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 increasing” in Holland; and by parallelism of the trend among Czechosiovakian urban intelligentsia and industrial and rural workers (Prokopec, 1984). These observations, coupled with the fact that the secular trend in stature was still going strong in the 1970’sin some economically advanced groups or nations while it had halted in others (Roche, 19791,seem to indicate the operation of more specificfactors than just the change in socioeconomic conditions. Thus, the “environmental hypothesis”may be falsified. We are in no position at present to advance a fully constructed alternate hypothesis. Some possibilities, however, should be indicated. Heritability of body height is considerable: 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 environmental 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 variability of such combined socioeconomic factors 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 differences in average stature observed between members of the most socioeconomicallycontrasting segments of ethnically relatively homogeneous nations do not exceed 1 standard 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 (PolandTable 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 situation. Therefore alteration of the genetic endowement is suggested. As a cause of such genetic background for the secular trend a change in mating practices 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, Holland). These countries had low coefficients of inbreeding already in the 19th century (Henneberg, 1979) before most of the trend took place. Our AE peoples were mixing considerably with migrants from all over Europe, and to some extent with native people, thus increasing their heterozygosity, but the trend among them was slow. It seems rather that some selective mechanism 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 adaptive 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 regulation of growth. LITERATURE CITED BielickiT,SzczotkaH, Gorny S, and CharzewskiJ (1981) Rozwarstwienie spd’eczne ws aczesnej ludnosci Polski: Analiza wysokosci ciala po\orowych urodzonych w 1957 r. Przegl. Antropol. 47:237-261. Bielicki T. and Welon Z (1964)Operation of the natural selection on the head form. Homo 14:22,23. Bielicki T, and Welon Z (1982)Growth data as indicators of social inequalities: the case of Poland. Yearb. Phys. Anthropol. 25:153-167. Brown HM (1935) Our land: is our o ulation satisfactory? The results of inspection of! ckldren of school ages. S. Afr. Med. J. 13:819-824. CalcagnoM, and Gibson KR (1988)Human dental reduction: natural selectionor the probable mutation effect. Am. J. Phys. Anthropol. 77:505-517. Cameron N (1979)The growth of London schoolchildren 19041966; an analysis of secular trend and intracounty variation. Ann. Hum. Biol. 6.50.5-525. Cavalli-Sforza LL, and Bodmer WF (1971)The Genetics of Human Populations. San Francisco: Freeman. Chiarelli B (1977)On the secular trend in stature:Abody constitution interpretation. Curr. Anthrop. 18523526. Cluver EH (1935) Physical tests a plied to the white population of the Union. S. Afr. d d . J. 132325,826. Cluver EH, Jokl E, and Rorich PR (1946)The physi ue of American, Canadian, En lish and South d i c a n school children. S. Afr. J. &fed. Sci. 11:45-49.
SOCIOECONOMIC CAUSATION Eveleth D, and Tanner J M (1976)Worldwide Variation in Human Growth. Cambridge: Cambridge University Press. Frayer D (1984) Biological and cultural change in the Euro ean Late Pleistoceneand Early Holocene. In FH SmitR and F Spencer (eds.): The Origins of Modern Humans: A World Survey of the Fossil Evidence. New York: Alan R. Liss, Inc., pp. 211-250. Gouws A, and van der Menve J (1987)Heights, weights and growth rate of Bloemfontein females aged 7 to 19 years of age. S. Afr. J. Sci. 83:378. Grobbelaar CS (1967)A University of Stellenbosch contribution to the hysical anthropolo of the white poulation of Souti Africa. S.Afr. J. gience 63:401415. i5enriebai-gX i1976! The ir,f!xence nf natural selection on brachycephalizationin Poland. Stud. Phys. Anthropol. 2~3-19. Henneberg M (1979)Breeding isolation between populations; theoretical model of mating distances distribution. Stud. Phys. Anthropol. 5:81-94. HennebergM (1988)Decrease of human skull size in the Holocene. Hum. Biol. 60:395-405. Henneber M, Budnik A, Pezacka M, and Puch AE (1985)&ead size, body size, and intelligence:intraspecific correlations in Homo sapiens sapiens. Homo 36:207-218. Jedlinska W (1985) Wplyw niektorych czynnikow srodowiska s olecznego na wysokosc ciala dzieci szkolnych w Porsce. Przegl. Antropol. 51:15-37. Kotze JP, Williams WN, MacIntyre U, and de Hoo ME (1986) Anthropometric and dental data on didrent ppulation groups in South African primary schools. . Afr. J. Sci. 82329-333. Krogman WM, and IsCan MY (1986)The Human Skeleton in Forensic Medicine. Springfield, IL: C.C. Thomas. Lurie GM (1958)Hei hts and weights of Euro ean and Med. J. Coloured school chiydren in Cape Town. S. 32:1017-1025. MalinowskiA, and Strzalko J (1970)Stan rozwoju somat cznego studentow I roku Akademii Medycznej w Joznaniu. Zdrowie Publiczne 7:611-617. Mueller WH i1976) Parent-child correlations for stature and weight smaag school aged children: a review of 24 studies. Hum. Biol. 48:37%397. Piontek J (1971) Ocena stanu rozwo'u fiz cznego poborowych powiatow Inowroclaw and kuchofa urodzonych w drugiej potowie XIX wieku, w porownaniu z
d.
465
wspolczesna,mlodzieza,Pomorza i Kujaw. In Rozwoj i Dorobek Antropologii Polskiej w 25-Leciu PRL. Poznan: UAM, pp. 71-75. Price B, Cameron N, and Tobias PV (1987) A further search for a secular trend of adult body size in South African blacks: evidence from the femur and tibia. Hum. Biol. 59:467475. Prokopec M (1984) Secular trends in bod size and ro ortions, and their biological meaning. &ud. Hum. kco!. 6~37-61. Richardson BD (1978)Growth patterns of South African children: an overview. S.Afr. J. Sci. 74:246-249. Roberts DF, Billewicz WZ, and McGregor IA (1978) Heritabilitv of stature in a West African population. Ann. Hum:Genet. 4215-24. Roche AF (19791 Secular trends in stature, weight and maturation. Monog. Soc. iias. Child h v . 12:2-2?. Rosenbaum S,Skinner RK, Knight IB, and Garrow S! (1985) A survey of heights and weights of adults in Great Britain, 1980. Ann. Hum. Biol. 12~115-127. Sloan AW (1967)Estimation of body fat in young men. J. Appl. Physiol.23:311-315. Stinson S (1985)Sex differencesin environmental sensitivity during growth and development. Yearb. Phys. Anthropol.28:123-147. Smit PJ, and Potgieter J F (1967)Body measurements of school children offour racial groups in Pretoria. S. Afr. Med. J. [Suppl.l41:86&886. Tobias PV (1975) Stature and secular trend among Southern African Negroes and San (Bushmen).S.Afr. J. Med. Sci. 40:145-164. Tobias PV (1985) The negative secular trend. J. Hum. EvoI. 14:347-356. TobiasPV, and Netscher D (1977)Reversal ofthe secular trend, as evidenced by South African Negro crania and femora. Hum. Biol. 59:467475. Van den Berg ER (1990) Absence of a positive secular trend in an affluent South African community: 18031989, an unpublished BSc(MedXHons1thesis. University of CapeTown. Van Wieringen JC (1986) Secular owth chan es. In F Falkner and JM Tanner (eds.):g m a n Grow&, Vol. 3 Methodology Ecological, Genetic, and Nutritional Effects on Growth. New York Plenum, pp. 307-331. Wolanski N (1978) Secular trend in man: evidence and factors. Coli. Anthropoi. 2:69-86. Wrzosek A (1931) 0 stosunku niektorych pomiarow antropologicznych i typow rasowych morfologicznych do sprawnosci umyslowej. Przegl. Antropol. 5:l-16.
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 examiningtrends in different socioeconomicgroups 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 40:145164,1975),but the overall directionis positive with a slow rate (0.24cddecade for 72 Negroid male groups and 0.48 c d d for 28 Khoisan male samples). Magnitude of the trend among adult AE (0.41c d d for females, 0.59 for males) does not differ significantlyfrom that among natives. The trend was absent,in the data for 10-year-oldAE boys and girls. The rate of trend among AE is much lower than that in their countries of origin (mainlyHolland 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 c d d ) . It follows that the explanation of the secular trend as being an ecosensitive response of individuals to changing levels of well-beingis insufficient.
The human species is continuously undergoing a number of microevolutionary changes. Whether these are adaptive in character or due to random forces is debatable. It is also uncertain whether some are true microevolutionary phenomena due to changing fre uencies of alleles in the gene pools or whet 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 determined 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
x
0 1990 WILEY-LISS, INC.
from uniform (Tobias and Netscher, 1977; Wolanski, 1978; Cameron, 1979; Roche, 1979; Tobias, 1985; Van Wieringen, 1986, Price et al., 1987). Although the most common view is that the trend occurs as an ecosensitivechange 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 natuReceived August 15,1989; accepted May 16,1990. M. Henneberg is now a t Department of Anatomy and Human Biology, University of the Witwatersrand Medical School, Parktown 2193, Johannesburg, South Africa.
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, brachycephalization (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 h i t e d body of coincident facts. The most common explanation in the literature on secular trends is that direction and tempo of the trend are reflections of changes in the socioeconomicsituation. This explanation is based on a simple coincidence between stature increase in a given nation and this nation’s improving socioeconomicconditions. Less attention was paid to comparisons of trends in different socioeconomic subpopulations of the same nation. Such comparisons offer an opportunity to test the hypothesis tying secular change to socioeconomic change. The aim of this paper is to present this test. According to the “environmental hypothesis,’any trend due exclusivelyto an ecosensitive 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 socioeconomiccircumstances in various populations, and 2) direction andor magnitude of the trend in sectors of the same nation showingdifferent dynamics of socioeconomic change should differ accordingly. Southern Africa, with its stark contrasts in opportunities for socioeconomic advancement between various sectors of the population, offers a good opportunity to test the environmental hypothesis. Some information useful in further testing of the hypothesis 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)skeletonsof 41 adult males and 45 adult females born between the years 1803and 1922 buried at the
“white” upper-class cemetery in Wynberg, Cape Town (van den Berg 1990), 2) anthropometric measurements of the “white”firstyear medical students at the University of Ca e Town durin 1988 and 1989 (86 males, 63females), and 3 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 emotianal connotations. Throughout this paper we shall use the following terms that we feel shodd be perceived as Qhjectiveand no%offensive: African of European extraction (N3k-a member of a population whose ancestors came mainly from Holland and England (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 frustrated in their traditional advancement as well as in the Western-styleurbanization by European colonization of their territories and by oppressive legislation. Many tribes differed between themselves socioeconomically and were at various times treated differently 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 areas, situated below Negroids in the socioeconomic hierarchy. Some Khoisan groups pursued their traditional lifestyle well into the 20th century. Like Negroids, they were denied political rights and had only a very limited opportunity for economic advancement. In this paper a collective term, “natives,”will be sometimes used to describe iointlv Nemroids and Khoisan. The cliche of “whit‘k“a d “black peoples is too simplistic
5
46 1
SOCIOECONOMIC CAUSATION TABLE 1 . Body height of young (18+ years old) South African adult males of European extraction Year examined
Height (mm)
Group
Author
1877l 1935
1,722 1,729
v a n den Berg (1990) Brown (1935)
1935
1,736
1966
1,775
1966
1,773
1973
1,745
l94P
1 79.1
Wynberg Cemetery Cape Province Secondary Schools Special Service soldiers, Pretoria Bloemfontein, OFS Secondary schools Univ. of Cape Town students, Med. Sch. Johannesburg, Secondarv Schools IJniv of Cape Town students, Med. Sch.
Cluver (1935) Grobbelaar (1967) Sloan (1967) Richardson (1978) Own d a t a
‘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
1,609 1,618
van den Berg (1990) Brown (1935)
1966
1,646
1978
1,625
1986
1,660
1988
1,649
Wynberg Cemetery Cape Province Secondary Schools Bloemfontein, OFS Secondary Schools Johannesburg Secondary Schools Bloemfontein OFS students Univ. of Cape Town students. Med. Sch.
Grobbelaar (1967) Richardson (1978) Gouws and van der Merwe (1987) Own data
‘Average year of birth plus 20 years
to be applied to the complex situation of the subcontinent. For instance, “black in certain situations will include immigrants from India, South-East Asia, and “coloured people 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 formulae (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 millimeter during special anthropometry practicals.’ These AE data were supplemented by statures of medical students and other young AE adults measured earlier and reported 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 averages for geographically close peoples measured 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 better than do individual data point comparheight was regressed on the year ofpexamina- isons. In both males and females, increase in tion, assuming for the skeletal material the body height was approximately 0.5 cm per year of examination to be 20 years after the decade. No significant increase was found in average birthdate. Linearity of regression statures of 10year-old AE children. Slopes of was tested by comparing goodness-of-fit of respective regression lines, taken at their straight lines and an array of various curvi- face value, indicate little change (Table 4). linear models applied to the data. Regression The trend among Negroid adult males is slopes and correlation coefficients were de- linear, significant, and positive. The numertermined and their significance was evalu- ical value of the slope indicates a tempo ated by means of t-tests. The significance of slower than that among adult AE, but the differences between slopes of regression difference between Negroid and AE slopes is lines and between correlation coefficients not significant. The trend among Khoisan xgas decn,.";n* Illllld by means sf cmfidence in- males is similar to that fwnd among-AE.The tervals. A conventional significance level of confidence intervals of Khoisan, Negroid, 0.05 was used throughout unless otherwise and AE slo es overlap each other considerindicated. ably; thus t e tempos of the three trends do not differ significantly.
K
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
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 tabulated 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 1978 1985 1986
1,356 1,372 1,378 1,416 1.391
1,356 1,361 1,416 1,424 1.409 1,309 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)
i,3ii
1,399 __
TABLE 4. Correlation coefficients and slopes of linear regressions of body height on the year of examination for Southern African groups'
Data set European adult males European adult females European 10 year-old boys European 10 year-old girls "Negroid" adult males2 Khoi-San adult males" Polish adult males'
N (groups)
r
Slope
7 6 7 8 72 28 7
0.81 0.83 0.01 0.25 0.24 0.54 0.95
0.59 0.41 0.10 0.59 0.24 0.48 1.14
'Data for better-off Polish males (Table 5) are included for comparison. 'Data from Tobias (1975).
Limits of 95% confidence interv. Lower Upper
Signif. o f slope P
0.09 0.04 - 2.14 - 1.65 0.01 0.17 0.90
0.03 0.04 (0.91) ins (0.54) ins 0.04 0.003 0.0009
1.09 0.78 2.34 2.83 0.47 0.79 1.92
463
SOCIOECONOMIC CAUSATION
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 magnitude of trends in groups of various origin are similar, despite substantial socioeconomic 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 countries of the northern hemisphere where tempos often exceeded 1cddecade (e.g., Prokopec, 1984; Stinson, 1985; van Wieringen, 1986). One of the possible ex lanations of the weakness of trends in bot the natives and AE is that suggested by Tobias (1985),who postulated that “have-most”people show absence of the positive trend since they have already reached the upper phenotypic limit
r:
1200
{ L
_____ 1880
-
/___?_.
1900
1920
1940
-__ 1960
B
--
1980
set by their genetic endowment, while the absence of the positive trend among “havelittle” 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 “environmental” explanation of secular trends were true one would predict that in countries where peoples of lower socioeconomicstanding 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 using Polish male data. Polish medical students in 1930’s and in the 1980’s were coming from a similar socioeconomicstratum of the society, despite post-war efforts at eradicaton 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 socioeconomicsituation of students could have only worsened, or at least did not improve much, due to the social and economic policies in post-war Poland disadvantaging educated people. These policies caused economic advancement of poorer sectors of the society. Thus body heights of all conscripts in the country, where approximately 5% of people had university education, should increase faster than those of medical students. Polish students coming from hi her socioeconomic-status groups were in eed taller than an average Polish 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 c d decade).
2000
yr
Fi 1 The secular trend of body height among affluent 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.
TABLE 5. Body heights of Polish better-off young adult males’ Year
Height (mm)
Group
Author
1885 1915 1925 1930 1957 1967 1983
1,650 1,655 1,669 1,706 1,734 1,760 1,770
Selected conscripts Selected conscripts Conscripts Medical students Medical students Mecical students Medical students
Piontek (1971) Piontek (1971) Piontek (1971) Wrzosek (1931) Malinowski and Strzalko (1970) Malinowski and Strzalko (1970) 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 different socioeconomicreasons, 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 (19301959) 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 increasing” in Holland; and by parallelism of the trend among Czechosiovakian urban intelligentsia and industrial and rural workers (Prokopec, 1984). These observations, coupled with the fact that the secular trend in stature was still going strong in the 1970’sin some economically advanced groups or nations while it had halted in others (Roche, 19791,seem to indicate the operation of more specificfactors than just the change in socioeconomic conditions. Thus, the “environmental hypothesis”may be falsified. We are in no position at present to advance a fully constructed alternate hypothesis. Some possibilities, however, should be indicated. Heritability of body height is considerable: 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 environmental 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 variability of such combined socioeconomic factors 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 differences in average stature observed between members of the most socioeconomicallycontrasting segments of ethnically relatively homogeneous nations do not exceed 1 standard 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 (PolandTable 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 situation. Therefore alteration of the genetic endowement is suggested. As a cause of such genetic background for the secular trend a change in mating practices 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, Holland). These countries had low coefficients of inbreeding already in the 19th century (Henneberg, 1979) before most of the trend took place. Our AE peoples were mixing considerably with migrants from all over Europe, and to some extent with native people, thus increasing their heterozygosity, but the trend among them was slow. It seems rather that some selective mechanism 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 adaptive 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 regulation of growth. LITERATURE CITED BielickiT,SzczotkaH, Gorny S, and CharzewskiJ (1981) Rozwarstwienie spd’eczne ws aczesnej ludnosci Polski: Analiza wysokosci ciala po\orowych urodzonych w 1957 r. Przegl. Antropol. 47:237-261. Bielicki T. and Welon Z (1964)Operation of the natural selection on the head form. Homo 14:22,23. Bielicki T, and Welon Z (1982)Growth data as indicators of social inequalities: the case of Poland. Yearb. Phys. Anthropol. 25:153-167. Brown HM (1935) Our land: is our o ulation satisfactory? The results of inspection of! ckldren of school ages. S. Afr. Med. J. 13:819-824. CalcagnoM, and Gibson KR (1988)Human dental reduction: natural selectionor the probable mutation effect. Am. J. Phys. Anthropol. 77:505-517. Cameron N (1979)The growth of London schoolchildren 19041966; an analysis of secular trend and intracounty variation. Ann. Hum. Biol. 6.50.5-525. Cavalli-Sforza LL, and Bodmer WF (1971)The Genetics of Human Populations. San Francisco: Freeman. Chiarelli B (1977)On the secular trend in stature:Abody constitution interpretation. Curr. Anthrop. 18523526. Cluver EH (1935) Physical tests a plied to the white population of the Union. S. Afr. d d . J. 132325,826. Cluver EH, Jokl E, and Rorich PR (1946)The physi ue of American, Canadian, En lish and South d i c a n school children. S. Afr. J. &fed. Sci. 11:45-49.
SOCIOECONOMIC CAUSATION Eveleth D, and Tanner J M (1976)Worldwide Variation in Human Growth. Cambridge: Cambridge University Press. Frayer D (1984) Biological and cultural change in the Euro ean Late Pleistoceneand Early Holocene. In FH SmitR and F Spencer (eds.): The Origins of Modern Humans: A World Survey of the Fossil Evidence. New York: Alan R. Liss, Inc., pp. 211-250. Gouws A, and van der Menve J (1987)Heights, weights and growth rate of Bloemfontein females aged 7 to 19 years of age. S. Afr. J. Sci. 83:378. Grobbelaar CS (1967)A University of Stellenbosch contribution to the hysical anthropolo of the white poulation of Souti Africa. S.Afr. J. gience 63:401415. i5enriebai-gX i1976! The ir,f!xence nf natural selection on brachycephalizationin Poland. Stud. Phys. Anthropol. 2~3-19. Henneberg M (1979)Breeding isolation between populations; theoretical model of mating distances distribution. Stud. Phys. Anthropol. 5:81-94. HennebergM (1988)Decrease of human skull size in the Holocene. Hum. Biol. 60:395-405. Henneber M, Budnik A, Pezacka M, and Puch AE (1985)&ead size, body size, and intelligence:intraspecific correlations in Homo sapiens sapiens. Homo 36:207-218. Jedlinska W (1985) Wplyw niektorych czynnikow srodowiska s olecznego na wysokosc ciala dzieci szkolnych w Porsce. Przegl. Antropol. 51:15-37. Kotze JP, Williams WN, MacIntyre U, and de Hoo ME (1986) Anthropometric and dental data on didrent ppulation groups in South African primary schools. . Afr. J. Sci. 82329-333. Krogman WM, and IsCan MY (1986)The Human Skeleton in Forensic Medicine. Springfield, IL: C.C. Thomas. Lurie GM (1958)Hei hts and weights of Euro ean and Med. J. Coloured school chiydren in Cape Town. S. 32:1017-1025. MalinowskiA, and Strzalko J (1970)Stan rozwoju somat cznego studentow I roku Akademii Medycznej w Joznaniu. Zdrowie Publiczne 7:611-617. Mueller WH i1976) Parent-child correlations for stature and weight smaag school aged children: a review of 24 studies. Hum. Biol. 48:37%397. Piontek J (1971) Ocena stanu rozwo'u fiz cznego poborowych powiatow Inowroclaw and kuchofa urodzonych w drugiej potowie XIX wieku, w porownaniu z
d.
465
wspolczesna,mlodzieza,Pomorza i Kujaw. In Rozwoj i Dorobek Antropologii Polskiej w 25-Leciu PRL. Poznan: UAM, pp. 71-75. Price B, Cameron N, and Tobias PV (1987) A further search for a secular trend of adult body size in South African blacks: evidence from the femur and tibia. Hum. Biol. 59:467475. Prokopec M (1984) Secular trends in bod size and ro ortions, and their biological meaning. &ud. Hum. kco!. 6~37-61. Richardson BD (1978)Growth patterns of South African children: an overview. S.Afr. J. Sci. 74:246-249. Roberts DF, Billewicz WZ, and McGregor IA (1978) Heritabilitv of stature in a West African population. Ann. Hum:Genet. 4215-24. Roche AF (19791 Secular trends in stature, weight and maturation. Monog. Soc. iias. Child h v . 12:2-2?. Rosenbaum S,Skinner RK, Knight IB, and Garrow S! (1985) A survey of heights and weights of adults in Great Britain, 1980. Ann. Hum. Biol. 12~115-127. Sloan AW (1967)Estimation of body fat in young men. J. Appl. Physiol.23:311-315. Stinson S (1985)Sex differencesin environmental sensitivity during growth and development. Yearb. Phys. Anthropol.28:123-147. Smit PJ, and Potgieter J F (1967)Body measurements of school children offour racial groups in Pretoria. S. Afr. Med. J. [Suppl.l41:86&886. Tobias PV (1975) Stature and secular trend among Southern African Negroes and San (Bushmen).S.Afr. J. Med. Sci. 40:145-164. Tobias PV (1985) The negative secular trend. J. Hum. EvoI. 14:347-356. TobiasPV, and Netscher D (1977)Reversal ofthe secular trend, as evidenced by South African Negro crania and femora. Hum. Biol. 59:467475. Van den Berg ER (1990) Absence of a positive secular trend in an affluent South African community: 18031989, an unpublished BSc(MedXHons1thesis. University of CapeTown. Van Wieringen JC (1986) Secular owth chan es. In F Falkner and JM Tanner (eds.):g m a n Grow&, Vol. 3 Methodology Ecological, Genetic, and Nutritional Effects on Growth. New York Plenum, pp. 307-331. Wolanski N (1978) Secular trend in man: evidence and factors. Coli. Anthropoi. 2:69-86. Wrzosek A (1931) 0 stosunku niektorych pomiarow antropologicznych i typow rasowych morfologicznych do sprawnosci umyslowej. Przegl. Antropol. 5:l-16.
