AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 66:407-416 (1985) Ecological Factors in Skin Color Variation Among Papua New Guineans ROBIN G. HARVEY SubDepartment of Anthropology, British Museum (Natural History), London SW7 5BD, England KEY WORDS Papua New Guinea, Skin color, Reflectance spectrophotometry ABSTRACT An EEL reflectance spectrophotometer was used to measure the skin color of the inner upper arm and the forearm of 913 Karkar Islanders (Madang District) and 684 Lufa villagers (Eastern Highlands District). The samples were subdivided to study sex, age, and population variation against a background of ecological observations, including sunlight exposure, clothing, and erythemally effective wavelengths of ultraviolet light (Robertson, unpublished Ph.D. thesis, 1974). Population differences in sex and age variation in upper arm skin color may largely be attributable to the effects of culturally associated clothing differences. Not only do the Lufa villagers wear substantially less clothing than the Karkars, but also their arms are exposed more frequently to ultraviolet light during heavy manual work in unshaded gardens. For the melanin content of the forearm skin there are similar patterns of age variation in both populations; however, the populations differ in mean percentage of reflectance throughout most of the age span. These betweenpopulation differences are interpreted as a consequence of greater average daily exposure to sunlight and the higher intensity of ultraviolet light in the highland environment. On the forearm the percentage of reflectance at 685 nm decreases more rapidly with age in the prepubertal and adult age groups, a result attributed to endocrine changes superimposed on cumulative changes in the melanin pigmentary mechanism. Studies of the variation in skin color with age by reflectance spectrophotometry have shown that age trends are variable between different human populations (Conway and Baker, 1972; Kahlon, 1976; Byard and Lees, 1982). There appears to be a general tendency for melanin pigmentation to increase from early childhood to adolescence, and this may become more pronounced around puberty. After puberty the pattern of variation seems to depend on whether melanization is being measured on skin surfaces frequently exposed to sunlight or on surfaces generally shielded from solar ultraviolet radiation. Even brief exposure to ultraviolet light W L ) may result in persistent changes in the cutaneous pigmentary system; therefore, it is virtually impossible to isolate through reflectance measurements alone the characteristics of what Quevedo et al. (1975)have termed 0 1985 ALAN R.LISS, INC. “constitutive” skin color (the genetically determined melanin pigmentation of the skin generated in the absence of light radiation influences) from those of “facultative” or inducible skin color. Some progress can be expected, however, if opportunities are taken to examine quantitative characteristics of cutaneous pigmentation against a background of ecological factors in human population studies. The International Biological Programmemuman Adaptability Project (IBP/ HA) fieldwork on coastal and highland Papua New Guineans, conducted between 1968 and 1972, provided one such opportunity. This report concerns the spectrophotometric characteristics of skin color in two Papua New Guinea populations living under conReceived April 20, 1984; revised October 9, 1984; accepted October 18.1984. 408 R.G. HARVEY trasting environmental conditions-one in the coastal lowland region of the Madang District on the volcanic island of Karkar, the other in the Eastern Highlands District, a t Lufa on the slopes of Mt. Michael. Age changes in melanization of inner upper arm and forearm skin surfaces are examined cross sectionally against the background of genetic, ecological, and sociocultural differences between these two Melanesian populations. MATERIALS AND METHODS The Karkar Island sample consisted of 407 males and 506 females from seven villages in the northern, Waskia-speaking part of the island (N = 821) and two villages in the southern, Takia-speaking part (N = 92). All the villages were situated at a n altitude less than 150 m. Serological and biochemical genetic differences between these two language groups have been reported (Boyce et al., 1978; Serjeantson et al., 1983). Initially, therefore, their skin reflectance measurements were analyzed separately. As no significant differences were found, Waskia and Takia results were amalgamated. The Lufa sample consisted of 310 males and 374 females from seven Yagaria-speaking villages of Lufa subdistrict, situated at a n altitude of approximately 1,900 m. The age structure of the Karkar and Lufa samples is given in Table 1. Considerable ecological differences exist between the two populations (Budd et al., 1974; Norgan et al., 1974; Hornabrook, 1977). The Karkar Islanders live in a hot, humid environment and cultivate gardens of food crops for subsistence and coconut plantations with cocoa for cash. Europeans introduced new religious practices and Western-style clothing a t the end of the nineteenth century, in contrast to the Lufa highlanders, where first contacts were made during the 1930s and had little cultural impact. At the time of the IBP/HA study the highlanders were mainly engaged in subsistence horticulture, which involved strenuous physical activity in steep terrain. Their life-styles had been influenced considerably less by external factors than those of the coastal villagers of Karkar Island. Measurements of cutaneous pigmentation were made with a n EEL reflectance spectrophotometer a t two sites, the inner upper arm and the forearm. All measurements were taken by the author, and the same galvanometer unit, applicator head, and light bulb were used a t both localities. The skin was cleansed before measurement and three filters of the EEL instrument were used (601, 605, and 609), giving percentage of reflectance readings at 425 nm, 545 nm, and 685 nm. Observations of the amount of time spent in sunlight (whether or not it was strong enough to cast shadows) during daily activities were obtained for 26 males and 30 females of Karkar and 29 individuals of each sex a t Lufa, using the technique of direct observation and logging. Subjects were followed continuously during the hours of daylight and records were made every minute of their status with regard to sunlight exposure. The individuals sampled were engaged in a pattern of activities that was considered representative of the village populations chosen for the investigation of skin color. The observations were made by Dr. G. M. Budd and Dr. Leigh Hendrie of Sydney University TABLE 1. Age structure of the Karkar and Lufa samples Age (years) Under 5 5-10' 10-15 15-20 20-30 30-40 40-50 50-60 Over 60 Total Males (N) 26 75 59 29 69 73 37 25 14 407 '5.001-10.000, and so forth. Karkar Females (N) 21 71 81 69 102 72 47 33 10 506 Males (N) 4 37 51 30 56 67 43 21 1 310 Lufa Females (N) 6 40 58 41 90 86 45 8 374 SKIN COLOR VARIATION AMONG PAPUA during a study of thermal stress. Skin reflectance measurements, taken by the author a t the same time a s this study, are available for 99 of the sunlight exposure (SE)subjects aged between 14.8 and 32.0 years and are summarized with the total skin color samples (>20 years) in Table 2. RESULTS Skin site and population differences The majority of interpopulation comparisons by other authors have been made on samples of adults. Initially, therefore, in Table 2 the results for the major samples are presented for individuals over 20 years of age. Mean percentage of reflectance from the upper arm is greater than from the forearm. The largest skin site differences occur a t the longest wavelength (685 nm), where they range from 8.8 to 11.8% in the large population samples and between 7.4 to 11.5% in the sunlight exposure (SE) samples. The highest coefficients of variation are found in the upper arm measurements at 545 nm (14.818.1%). In the large population samples the reflectance values are higher in females than in males at both skin sites and a t all wavelengths. Differences are significant in both populations in forearm reflectance (P < 0.05) and fail in only two instances to reach the 5%level of significance in upper arm reflectance (Lufa 425 nm and 685 nm). Sex differences are greatest in the upper arm measurements of the Karkar Islanders. In the sunlight exposure samples the results follow a very similar pattern. The majority of the reflectance values are higher in the females than in the males, significantly so in the forearm measurements. Skin site differences within populations are significant at all wavelengths. With one exception (males, upper arm, 685 nm), Lufa skins reflect less light than those of the Karkar Islanders. The lighter skin color of the Karkars is most clearly evident on the forearm, where all the interpopulation differences are highly significant (P < 0.0001). The frequency distributions of reflectance measurements show significant positive skewness, with the exception of the upper arm measurements a t 685 nm. Log transformations of reflectance measurements were made in a n attempt to normalize the distributions. An antilog transformation of reflectance measurements was also attempted, 409 following the recommendations of Harrison and Owen (1964). The effects of the transformations on each of the four principal subsamples was so inconsistent that they were abandoned in favor of using the original raw percentage values. The significance test used (the standardized normal deviate) was appropriate for sample distributions with varying degrees of skewness. Age changes The analysis of age-related changes in skin color concerns measurements a t 685 nm. Reflected light at this wavelength is influenced maximally by the concentration of melanin in the skin and minimally by the amount of blood flow (Harrison and Owen, 1956; Harmse, 1964). Figure 1 shows mean percentage of reflectance a t 685 nm plotted against age, subdivided by 5- and 10-year cohorts, for the upper arm. Clearly the age trends in the two populations are substantially different. For the Karkar Islanders the sex differences noted in the adult samples are evident in the separate age cohorts and are especially marked around 5-10 years and 20-40 years. In both sexes the mean values of percentage of reflectance reach their lowest levels around 10-15 years and increase sharply during early adulthood, especially in females. From the 30-40-year cohort the means decrease and continue to decline into late adulthood (6070 years in these populations). Among the Lufans a n entirely different pattern of age variation occurs. There are no significant sex differences in any of the age cohorts, and, in contrast to the Karkars, their skin reflectance means show a decline from early childhood to 20-30 years, followed by a variable trend in the remaining adult period. There are large standard errors of the mean values in the 50-60-year age cohort, mainly because of the smaller numbers in these samples. The forearm reflectance measurements show a more consistent pattern of variation in both populations (Fig. 2). Percentage of reflectance values are correlated significantly with age, the highest correlation occurring in the Lufa males (r = -0.6471, the lowest in the Karkar females (r = -0.395). There is evidence in Figure 2 that the relationship with age may be composed of two components, the first of which (a prepubertal phase) shows a more rapid decline with age than the second, postpubertal and adult Karkar (M) SE Karkar (F) SE Lufa (M) SE Lufa (F) SE 215 22 265 27 189 23 229 25 217 22 265 27 189 23 229 25 7.38' 8.35' 7.70**lt 8.11t 6.38 6.48 6.91** 7.02** 9.62+ 10.81' 10.lO**,t 10.54' 9.14 9.33 9.31 9.58 Mean 1.14 1.44 0.88 1.00 0.67 0.77 0.74 0.91 1.43 1.53 1.44 1.37 1.25 1.43 1.52 1.11 SD 425 nm 1.08* 0.31 1.20% 0.92* 0.85* 0.42 0.57' 0.01 0.74* 0.77* 0.87* 0.40* 1.36* 0.62' 0.88' 0.86' El 8.80- 9.23+ 10.57' 9.90*'st 10.46' 7.84 8.00 8.65** 13.81t 14.96 15.02**,' 15.19' 13.29 13.49 13.79*' 14.24 Mean 0.05 for significance of g,. P < 0.05 for significance of sex difference-within-place, within-skin site. +P < 0.05 for significance of population difference-within-skin site, within-sex. "P c ** ~ Forearm . . . Uooer arm Karkar (M) SE Karkar (F) SE Lufa (M) SE Lufa (F) SE n 1.42 1.45 1.23 1 30 0.87 0.96 0.97 1.12 2.34 2.42 2.68 2.26 2.25 2.44 2.47 2.27 SD 545 nm 0.940.64 0.46% 0.17 1.01' -0.16 1.00* 0.98* 0.72* 0.840.59* 0.32 0.62' -0.25 0.85 ' 0.38 el 22.02' 25.04' 23.96";.' 25.89+ 19.01 19.61 21.06'* 21.77 30.78 32.43 33.24",' 34.07 30.83 31.10 31.58 31.93 Mean 3.21 3.29 3.20 3.65 2.56 2.88 2.83 2.97 4.41 3.98 4.42 3.87 4.51 4.51 4.44 3.92 685 nm SD 0.83' 1.01' 0.44' 1.38: 0.87 0.08 0.71' 0.89* 0.12 0.52 0.00 -0.01 0.13 -0.10 0.32 0.19 El 38.7 23.3 37.1 20.2 38.9 25.8 36.1 23.8 38.7 23.3 37.1 20.2 38.9 25.8 36.1 23.8 Age (mean) TABLE 2 Mean, standard deviation (SO), and skewness (g,) for the drstribution ofpercentage ofreflectance at three wavelengths in individuals over 20 years of age (major samples) and in sunlight exposure (SE) subjects aged 14-32 years P 0 SKIN COLOR VARIATION AMONG PAPUA 29 1 411 I Fig. 1. Variation with age of mean percentage of reflectance at 685 nm from the inner, upper arm. Vertical bars represent 2 1 SE. phase. To test this hypothesis the linear regression of individual reflectance values on age was calculated for two age groups, 2.014.9 years and 15-69 years. Menarche occurs at 15.6 years among the Karkar Islanders and 16.5 years among the villagers of Lufa CHarvey, 1974);therefore, the age cohorts selected give a good approximation to pre- and postpubertal stages of development. The regression and correlation coefficients are given in Table 3. Within each age grouping there are no significant differences between sexes or between populations in the slope of the linear regression equations. However, with the exception of the Lufa male samples, there are large and significant differences in slope between the regression lines for the pre- and postpubertal groups. The percentage of the total variation accounted for by the regression is generally higher in the older than in the younger group, reaching 14.4%in the sample of Lufa males over 15 years of age. Exposure to sunlight The incidence of exposure t o sunlight for the four samples in the direct observation study is given in Table 4. The men and women of Lufa were observed for a longer period than were those of Karkar, although the Karkar people had records compiled for a minimum of 120 hours. During their total daily activity the Lufa villagers spent nearly twice as long, on average, in the sun as the R.G. HARVEY 412 I... 28 - ia 16 I . 5 . . 10 I . 15 , . 20 I 25 35 45 55 >60 Age ( y r s ) Fig. 2. Variation with age of mean percentage of reflectance at 685 nm from the forearm. Vertical bars represent +_ 1SE. Karkar Islanders. Figure 3 shows the percentage of time spent in sunlight for hourly intervals throughout the day. It illustrates the substantial differences in exposure times between the two populations. Incidence of exposure is very similar among the men and women of Lufa, especially during the midday period when the sun is at its highest elevation. In contrast, the men of Karkar were more exposed to sunlight than the women during the period 12.00-15.00 hours. The pattern of exposure variation in the Karkar women suggests some measure of active avoidance of sunlight from midday until midafternoon. potheses, none of which are likely to be mutually exclusive. There may be host differences in the capacity of the skin to synthesize melanin, to transfer it to the keratinocytes of the epidermis, and to maintain it in response to UVL exposure, the socalled tanning capacity of the skin (Harrison and Owen, 1967). There may be geographical, seasonal and altitudinal variation in the intensity of erythemally effective natural UVL (Robertson, 1969). Duration of daily exposure to UVL and the shielding effect of clothing must also be taken into account, together with genetically determined differences in cutaneous pigmentation. Skin site differences The skin site, sex, and population differ- The contrast between upper arm and foences suggest several explanatory hy- rearm reflectance shown in Table 2 is probaDISCUSSION 413 SKIN COLOR VARIATION AMONG PAPUA TABLE 3. Linear regression and correlation coefficientsfor the relationship between 'ualues) and age (X ualues) for the forearm percentage of reflectance at 685 nm 0 Age groupipopulation 2.0-14.9 years Karkar (M) Karkar (F) Lufa (Mf Lufa (F) 15.0-69.0 years Karkar (MI Karkar (F) Lufa (M) Lufa (F) Regression coefficients b SD Correlation (r) N a 158 170 92 103 26.4 28.8 27.1 28.5 -0.237 +_ 0.066 -0.287 k 0.066 -0.297 +_ 0.113 -0.387 t 0.101 -0.278 -0.316 -0.266 -0.356 238 256 209 255 25.0 26.9 22.2 23.0 -0.083* k 0.014 -0.089" +_ 0.014 k 0.015 -0.090 -0.058** f 0.018 -0.354 -0.338 -0,385 -0.193 'P< .05,*'P< ,002, for slope differences between age groups, within populations. 90 - - 80 - 70- t z 60- u) 0 2 w 40 50 c. s .F 30 - ;2 0 10 C 1 0 1 1 7 8 9 I 10 I I . I 11 12 13 14 Hour of Day 1 I I I5 16 17 I 18 Fig. 3. Average hourly incidence (C) of exposure to sunlight for 26 males and 30 females of Karkar and 29 individuals of each sex at Lufa. TABLE 4. Incidence of exposure to sunlight during daily activities (auerages of all obseruations) Observation period ( m i d % Time in Sex N Karkar Males Fema1es 26 30 8,538 7,231 40.3 38.0 Lufa Males Females 29 29 34,361 27,559 76.0 76.6 Place sunlight 414 R.G. HARVEY bly due to two main factors. The first is a difference in the density of epidermal melanocytes in the inner upper arm compared with the forearm and thus in the tanning capacity of the two sites. Regional variations in melanocyte density over the body are well documented (Szabo, 1967), although there are no specific data of the type reported by Garcia et al. (1977, 1981) for the Solomon Islanders available for the inhabitants of Karkar Island and Lufa subdistrict. Secondly, there is a difference in the frequency and intensity of exposure to UVL resulting from the more sheltered anatomical position of the inner upper arm surface and, in certain cases, from the shielding effects of clothing. Skin site differences are a n established feature of reflectance studies on human populations (Ojikutu, 1965) and there are numerous reports of within-sex, within-population differences in percentage of reflectance from upper arm and lower arm sites (Leguebe, 1976). Tournel (1966),and Rigters-Aris (1973).Similar results have been obtained for the present study. Although there are some time-ofday differences in sunlight exposure for Karkar men and women (Fig. 31, there are no substantial within-population, within-sex differences in average exposure times (Table 4). Therefore, it is felt justifiable to propose a difference in tanning capacity to explain the contrast between male and female reflectance values, which are clearly demonstrated by both populations. The evidence that this contrast is largely independent of UVL exposure rates suggests that it may be a n example of genetically determined sexual dimorphism. Population differences The significant difference between Karkar and Lufa skin reflectance, which is so much more pronounced on the forearm than the upper arm, suggests that a combination of greater daily exposure to sunlight and higher Sex differences W L intensity in the highland environment To elucidate the contrast between Karkar may be responsible. This hypothesis finds and Lufa in the sex differences on the upper support in the observations of sunlight expoarm, two environmental factors have been sure (Table 4; Figure 31, which show marked examined the shielding effects of clothing contrasts between the coastal and highland and differential exposure to UVL. Villagers people. It is also supported by the observaof the coastal and highland communities had tions of Robertson (unpublished Ph.D. thesis, conspicuously different clothing habits. All 1974) who demonstrated that under clear of the Karkar Islanders wore some form of conditions at midday there is a n increase of Western-style clothing, which included shirts about 20% in the sun-tanning effectiveness and blouses with sleeves that covered all or of W L for every 1,500 m increase in altipart of the upper arm. Lufa clothing styles tude. This means that in the absence of macontrasted markedly with those of Karkar. jor climatic differences affecting UVL Very rarely were individuals observed with intensity at the two localities, the sun-tanWestern-style clothes. Virtually all the vil- ning effectiveness of the midday sun a t Lufa lagers were clad traditionally in a simple would be about 23%greater than at Karkar, arrangement of woven bark cloth hanging where none of the villages studied were more from a broad belt around the waist. Clothing than 150 m above sea level. was rarely worn on the upper part of the Geographical variation in the strength of body and the opportunity for solar UVL to erythema-producing wavelengths of solar reach the upper arm during outdoor activi- W L has not been investigated in Papua New ties was high in the Lufa population, espe- Guinea. However, data for seasonal fluctuacially during heavy manual work in the tions in intensity of these wavelengths have unshaded gardens. The upper arm reflec- been obtained for Goroka in the Eastern tance values for the Lufans thus represent, Highlands District (about 60 km from Lufa) to a much greater extent than those of the (Robertson, unpublished Ph.D. thesis, 1974). Karkars, the characteristics of facultative, as These data indicate that during the two seadistinct from constitutive, skin color. sons in which the skin reflectance fieldwork Sex differences in the tanned skin of UVL- was conducted (February to June on Karkar, exposed surfaces, such as the forearm and July to October at Lufa) average levels of UV forehead, have been reported for a number of radiation would have been similar for a given native peoples in tropical habitats; among altitude. Seasonal climatic differences affectthe reports are those of Barnicot (19581, ing the absolute potential for sun-tanning Walsh (19641,Huizinga (1965,1968),van Rijn- are therefore unlikely to be responsible for SKIN COLOR VARIATION AMONG PAPUA the observed population differences in forearm melanization, and it seems reasonable to conclude that the marked differences in exposure to sunlight and differences in UV intensity associated with altitude are the principal factors involved. Age changes in melanin pigmentation In upper arm reflectance, the between-population differences (Fig. 1)can probably be accounted for by the cultural differences in clothing between coastal and highland peoples, as already discussed, and by the field observation that during the life span of the Karkar Islanders their clothing habits change in a manner that influences the UVL exposure of the upper arm. At the time of the survey most of the Karkar children went about stripped to the waist, but around puberty both boys and girls adopted a preference for wearing shirts or blouses, many of which had sleeves that covered the top half of the upper arm. These clothing styles continued during adulthood but became more variable during later years when clothing above the waist was frequently discarded during work in the gardens. This may be a n important contributory factor in the postpubertal increase in upper arm reflectance, which can be considered, at least in part, as a manifestation of the UVL screening effect of upper arm clothing worn during early and middle adulthood. The numbers of Lufa children in the youngest age groups are small; however, the results suggest that during early childhood their upper arms are lighter than those of the Karkars. Further research is needed along lines similar to the ultrastructural studies of skin pigmentation by Garcia et al. (1983) to determine whether differences in melanocyte packaging of the keratinocytes, such as those found between Bougainville and Malaita Islanders, also occur among the genetically different populations of coast and highlands in Papua New Guinea. Such histological differences might affect age variation in measurements made by reflectance spectrophotometry. Whatever the cause of the observed differences, the age changes in upper arm reflectance at 685 nm in the Lufa villagers are unlikely to be the same a s those of the Karkars owing to the virtual absence of upper body clothing worn at Lufa, the lack of shade in the highland gardens, and the high daily exposure to W L in the highland environment. 415 With regard to age changes in the melanin pigmentation of the forearm skin, a tendency for mean percentage of reflectance at 685 nm to decrease with age on exposed skin surfaces was noted by Walsh (1964) in a study of Papua New Guineans from Mt. Hagen (Western Highlands District). A similar result has been found in the present study, but the main interest here is that the darkening process is more rapid before puberty than after. This is almost certainly due to endocrine changes (Conway and Baker, 1972; Kalla, 1973; Kahlon, 1976) superimposed on the cumulative changes in the melanin pigmentary mechanism resulting from frequent exposure to UVL (Quevedo et al., 1975; Mitchell, 1963). The latter can be expected to continue throughout the lifetime of the individual and probably accounts for the gradual and progressive increase in melanin pigmentation with age in adults of both populations. ACKNOWLEDGMENTS The author is indebted to Professor G.M. Budd (Sydney) for supplying sunlight exposure observations for the people of Karkar and Lufa and for his helpful criticism of this manuscript. The assistance of Dr. Leigh Hendrie (Sydney) in the collection of sunlight observations is gratefully acknowledged. Thanks are due to Dr. Bill Craig (Canberra) and Miss Kay Shaw (London) for their help with programming and computing. Dr. Don Robertson (Brisbane) generously gave advice and information on the measurement of erythemally effective W L . The inspiration and encouragement of the late Prof. R.J. Walsh (University of New South Wales) is very greatly appreciated. The author is grateful to Dr. Anthony J. Boyce (Oxford) for helpful comments on this manuscript. The fieldwork was supported by the Australian Academy of Science and the Royal Society (London). It was part of the joint Australian-UK H A W P project in Papua New Guinea. LITERATURE CITED Barnicot, NA (1958)Reflectometry of the skin in Southern Nigerians and in some mulattoes. Hum. Biol. 30:150-160. Boyce, AJ, Harrison, GA, Platt, CM, Hornabrook, RW, Serjeantson, S, Kirk, RL, and Booth, PB (1978)Migration and genetic diversity in an island population: Kar Kar, Papua New Guinea. Proc. R. Soc. Lond. Ser. B. 202~269-295. Budd, GM, Fox, RH, Hendrie, AL, and Hicks, KE (1974) A field survey of thermal stress in New Guinea vil- 416 R.G. HARVEY lagers. Phil. 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