Pergamon Applied Geochemistry, Vol. 12, pp. 517-525, 1997

0 1997 Elsevier Science Ltd

PII: so883-2927(97)ooo30-9 All rights reserved. Printed in Great Britain

088%2927/97 %17.OO+O.OCI

Mobility of Bell Beaker people revealed by strontium isotope ratios of tooth and bone: a study of southern Bavarian skeletal remains

Gisela Grupe Institut fur Anthropologic und Humangenetik, Richard-Wagner-StraBe 10, Munich D-80333, Germany

T. Douglas Price Department of Anthropology, 1180 Observatory Drive, University of Wisconsin, Madison, WI 53706-I 393,

U.S.A.

Peter Schriiter Anthropologische Staatssammlung, Karolinenplatz 2a, Munich D-80333, Germany

Frank Siillner Institut fur Allgemeine und Angewandte Geologie, LuisenstraDe 37, Munich D-80333, Germany

and

Clark M. Johnson and Brian L. Beard Department of Geology and Geophysics, 1215 W. Dayton St., Madison, WI 53706-1393, U.S.A.

(Received 1 August 1996; accepted in revisedform 29 January 1997)

Abstract-In order to contribute to the continuing discussion of the mobility of the late neolithic Bell Beaker people, 69 skeletons from southern Bavaria were analyzed for the 87Sr/86Sr isotope ratios in tooth enamel and compact bone. Whereas Sr isotope ratios in the enamel of the first permanent molar match the Sr isotopic composition at the place of early childhood, the respective value in the adult femoral bone matches the Sr isotope ratio characteristic of the place of residence over the last few years prior to death. Significant differences between *‘Sr/*?Sr in these tissues indicate that 17.525% of these individuals changed residence during their lifetime. The overall direction of the migration, according to archaeological finds from the area, was toward the southwest. A relative surplus of migrating females and two cases ofevidence for migration in children argue for the movement of small groups; exogamy might explain the higher numbers of immigrating females. With regard to current information on migration rates in prehistory, the southern Bavarian Bell Beaker people were indeed highly mobile, especially since the archaeometric method used in this study is likely to underestimate movement. 0 1997 Elsevier Science Ltd

INTRODUCTION

Bell Beaker and residential mobility

During the earlier Neolithic, central Europe was divided into a variety of regional cultures. Prestige objects, made of Cu and other materials, were distributed by trade; thus, the existence of specialized craftsmen by the late Neolithic is assumed (De Laet, 1994; Lfining, 1994). In the course of only a few centuries between 2500 and 2000 B.C. at the end of the Neolithic, Bell Beaker pottery, and presumably people, spread over large parts of Europe, from Portugal and Ireland to Hungary and from Scotland to Sicily and North Africa.

It is difficult to characterize the Bell Beaker as a culture in the formal sense. Particularly during the early part of the period, there is an absence of common house types, burial customs, or even utilitar- ian pottery. An early expansive Bell Beaker phase is assumed to have appeared along the Lower Rhine

River, followed by a split into 3 “regional groups”: the southern Bell Beaker with finds from Spain, Portugal, southern France and Italy; the western Bell Beaker with sites in central and northern France, Great Britain and Ireland, the Benelux countries, the Rhine region, and the north German lowlands; and finally the eastern group in Hungary, the Czech Republic and Slovakia, Austria, and southern Bavaria.

Human skeletal materials associated with Bell Beaker artifacts are morphologically distinct from those of the indigenous people of the earlier Neolithic and exhibit a new, short-headed “morphotype” (Gerhardt, 1978). In addition, there were very few known settlement sites or house structures from the period. The widely distributed Bell Beaker pottery, the absence of settlement, and the new physical type, thus required explanation and generated much speculation (Sangmeister, 1972). The Bell Beaker people, for example, were considered to have been metal pro- spectors, itinerant tinkers, or even warriors (Gerhardt, 1978). Other interpretations of the phenomenon

517

518 G. Grupe et al.

involved a highly mobile population that split into several groups as it moved across Europe. This population was thought to be specialized in prospect- ing, manufacturing, and trading prestige goods. Continuing archaeological investigations, however, raised new questions about the Bell Beaker. For example, the materials were not spread continuously across Europe, but rather were found in patchy, island-like concentrations, as in southern Bavaria. From this perspective, Engelhardt (1991), for exam- ple, prefers to view the Bell Beaker people as elite in a society in which social strata crystallized as the culmination of regional differentiation in the earlier Neolithic.

Thus, the debate about Bell Beaker continues, and the question of residential mobility remains unre- solved. Styles of pottery and other artifacts have been used instead of human remains to examine the question of mobility and diffusion. The goal of the research described here is to examine the question of Bell Beaker mobility from an archaeometric perspec- tive using the actual human skeletal remains for direct information on changes in residence. The question for our research is whether or not Bell Beaker people moved significant distances, or remained in the same area, during their lifetime. The focus of our investiga- tions is Bell Beaker burials in southern Bavaria. More than 100 Bell Beaker sites have been excavated in this area, with the majority found between the Danube and the Alps.

The remainder of this paper describes the approach that we are using-the characterization of bone and tooth using Sr isotope ratios, the geology and archaeology of southern Bavaria, the results of our analyses, and some conclusions regarding the ques- tion of Bell Beaker mobility.

The archaeometric approach

The mineral matrix of hard human tissues (bones and teeth) consists mainly of largely insoluble Ca phosphate hydroxyapatite [Cais(PG&,(GH)z]. Common substitution of Sr for Ca in this mineral produces high Sr concentrations in the order of 102- IO3 ppm in hard tissue. In nature, Sr occurs in the form of 4 stable isotopes (Faure, 1986): the most abundant is **Sr (approximately 82.53%), followed by *‘Sr and *‘?Jr (approximately 7.04% and 9.87%, respectively), whereas 84Sr is least abundant (approxi- mately 0.56%). We present relative variations in *‘Sr abundances in materials by calculating a ratio with the non-radiogenic isotope, *‘jSr, following standard convention (Faure, 1986). Since the relative mass differences between *‘Sr and 86Sr is so small, no isotopic fractionation takes place during Sr transport in any ecosystem (Graustein, 1989). For non-mobile individuals, the 87Sr/86Sr ratio in hard tissue will therefore match the Sr isotopic composition of their habitat. Because the earth’s surface is highly variable

in terms of bulk composition (affecting *‘Rb/*‘Sr ratios) and age, 87Sr/86Sr ratios on the surface are quite variable.

It should be possible, therefore, to trace changes in residence in animals through analysis of Sr isotope ratios in hard tissues that formed at different ontoge- netic stages (Ericson, 1985; Price et al., 1994a,b; Sealy er al., 1991, 1995). For this purpose, compact femoral bone and the dental enamel of the first permanent molar is used for analysis. Because of its rather low rate of turnover, compact femoral bone in adults contains Sr, which has been incorporated during the last 5-10 a of life. Dental enamel, however, as a cell- free tissue does not undergo turnover after formation, Thus, the Sr in the enamel of the first permanent molar contains Sr that has been incorporated from birth to approximately 4 a of age (Hillson, 1989). Differences in the Sr isotope signature between enamel and bone are therefore indicative of a change in residence during the individual’s lifetime. Such difference8 mean that the individual was born in a place geologically and isotopically different from the place where it died. Strontium isotope ratios in animal hard tissue have been used, for example, to identify the origin of illegally exported elephant ivory (Van Der Merwe et al., 1990; Vogel et al., 1990) or to reconstruct migration in salmon with appositional bone growth (Koch et al., 1992). Studies of humans have been reported for prehistoric American Indian groups in the Southwest United States (Price er al., 1994b; Ezzo et al., 1997) and aboriginal populations in South Africa (Sealy et al., 1991). A preliminary study of Bell Beaker skeletons, demonstrating the applicability of the method, was reported by Price et al. (1994b).

The geology of Bavaria

Geologically, Bavaria can be divided into several zones. The Danube River separates a southern and northern half (Fig. 1). The region northeast of the river is characterized by granites and gneisses with isotopic ratios exceeding 0.71. A rather detailed Sr isotopic map already exists for this area (Sollner, pers. commun.). Sediments south of the Danube are partly glacial in origin, resulting in loess deposits close to the river. This area south of the river has not been geologically mapped for Sr isotope ratios, but is characterized by lower values. For this reason, soil samples were collected from several sites, and Sr isotope ratios were measured in the sediments. The values for these samples ranged between 0.70899 and 0.70992 (Table 1); the mean and standard deviation for the four samples were 0.70938 and 0.00047, respectively.

The area covered by sediments along the Danube has been inhabited since. the earlier Stone Age. The sites of the Bell Beaker period are also indicated in Fig. 1, demonstrating the distribution of materials along the Danube River. The archaeological evidence leaves

Mobility of Bell Beaker people, use of Sr isotopes 519

Fig. 1. Geology of Bavaria divided into zones. The Danube River separates a southern and northern half

no doubt that the Bell Beaker people came from the (N)E and spread to the (S)W, following the rivers that provided water, food, and transport. Bell Beaker individuals, migrating from NE to SW through this area, should show differences in isotopic ratios between bone and enamel.

METHODOLOGY

The Bell Beaker skeletal material analyzed for this study is housed in the Anthropological Collection, Munich, Ger- many. The first permanent molar and compact cortical bone was sampled from all Bell Beaker skeletons where both

Table 1. Sr ppm and s’Sr/*?Sr ratios for soil samples from the study area. The values from Straubing and Osterhofen

are averages of samples

Site Sr ppm s7Sr/s6Sr

Kiinzing-Bruck 159 0.70902 Ktinzing-Bruck 163 0.70899 Straubing 166 0.70968 Osterhofen 164 0.70992

tissues were preserved. The skeletons had been found either in small burial sites (l&30 individuals: bsburg, hlbach, K+zing-Bruck, Landau, C&terhofen, Bichering) or as single burials or very small groups of burials (no more than 5 individua!s: &ltdorf, Landau, mnching, &mmelsbrunn, &aubing-Oberau, T&kelhausen). The underlined letters are used to designate each site in Fig. 1.

Bone and enamel samples were washed and the surfaces removed mechanically (in Madison) or by ultrasonic etching (5 min in 99% HCOOH, Munich), ashed for 12 h at 500°C to remove the organic fractions, and finally homogenized To about 100 mg of homogenized sample was added a spike of Sr (National Bureau of Standards, Washington, DC) with a ratio of Sr:spike of 1:50. Samples were then solubilized overnight in 3 ml of concentrated HNOs (Madison) or by wet-ashing under pressure for 6 h at 160°C in 1 ml concen- trated HNOs (Munich). After evaporation of the acid at 80°C the remnants were solubilized again in 3 ml of HCl and passed through a cation exchange column (20@-400 mesh, HCl as mobile phase) to separate Rb from Sr. The *‘Sr/*?3r ratio was determined by mass spectrometry. Standard reference material SRM 987 (National Bureau of Standards, Washington, DC) served as a quality control. In addition to 87Sr/86Sr ratios, the Sr content was also measured in the samples using the isotope dilution method.

The study was undertaken as a joint project between the Universities of Munich (Germany) and Wisconsin-Madison (U.S.A.). Approximately half the samples were analyzed at each locality. Several samples were analyzed in duplicate at the two laboratories for comparison of results. This compar-

520 G. Grupe et al.

Table 2. Comparison of non-standardized values from identical samples analyzed in Munich and Madison

Sr ppm s7Sr/86Sr

Sample Munich Madison Munich Madison

Landau, G.4,B 218 219 0.709164 0.708972 Weichering, G.D,T 126 131 0.712305 0.712821 Weichering, G.D,B 292 251 0.708740 0.708847

G: grave; B: bone; T: enamel.

ison was made to evaluate possible differences between laboratories in terms of instruments or procedures. These results (Table 2) demonstrate that the inter-laboratory results are directly comparable. However, because of instrument problems in Madison (3 different sets of collectors on the Madison mass spectrometer), all data have been standar- dized to base Madison measurements (Table 3).

Contamination of bone and tooth samples, or diagenesis, is a well-known problem in trace element analysis of human skeletal material (Price et al., 1992). However, diagenesis is not a substantial problem in Sr isotope analysis. Acid cleaning of bone samples is generally effective in removing most contaminants (Price et al., 1994b). In addition, any contaminants remaining in bone or enamel samples would exhibit 87Sr/8sSr ratios of the local geology. Thus, any values that indicate residential changes and different geogieal source materials are clearly not heavily contaminated.

RESULTS

The results of our analyses of tooth and bone from Bell Beaker burials in Bavaria are presented in Table 3. This table includes site and burial number, age and sex of the burial, s7Sr/*6Sr ratios and Sr ppm for tooth and bone samples from the burial. A total of 77 individuals are listed in the table. Two burials from the site of Weichering (Burials A and D) later were discovered to be younger, from the La Terre period of the Iron Age. Samples of bone or tooth were not available from 6 of the individuals. Thus, the Bell Beaker sample includes 69 individuals analyzed for both bone and tooth enamel. This is the largest sample of *7Sr/86Sr ratios in human tissues available any- where to date.

The number of burials and number of bone/tooth pairs of samples per site is given in Table 4. Age and sex information on the burials is summarized in Tables 5 and 6. These tables do not include the two Iron Age burials from Weichering.

Mean values for 87Sr/86Sr ratios and Sr ppm for tooth and bone samples are also presented in Table 3. Strontium values in tooth enamel (X-99) are sig- nificantly lower than in bone (X= 256) (cf. Figure 2). Mean values for 87Sr/86Sr ratios are higher in enamel (0.70967) than in bone (0.70904) as would be expected in a population with residential mobility, where individuals change their place of residence during life in a geologically variable area.

Several approaches could be used to distinguish immigrants using the Sr isotope data (cf. Ezzo et al.,

1997). Because of the variation that is present in soil and bone data, any cut-off value to distinguish migrants is regionally specific and somewhat arbi- trary. In this paper, we present and discuss two methods of determining the significance level for distinguishing immigrants:

(1) a value based on geological differences in the area, and

(2) a value based on bone Sr isotope ratios as an indicator of indigenous values in tooth enamel.

Although the geochemical differences in 87Sr/*aSr ratios for the geology of this area appear to be small, they are in fact highly significant. Modern mass spectrometers have a measurement error of between f 0.00003 and f 0.00001 for Sr isotope ratios. Thus, a difference of 0.001 (0.710-0.709) is the equivalent of between 33.3 and 100 measurement units, depending on the precision. Migration from a granite/gneiss area into a region dominated by carbonate-rich soils thus should be reflected in the *‘Sr/*‘Sr ratios in bone and enamel. Using a cut-off of 0.001 between the bone and enamel measurements, likely immigrants can be identified. Figure 3 shows burials from the Augsburg site. Immigrants are readily detected, and the geological boundary between granitelgneiss and carbonate soils, marked by the Danube River, is distinctive. Augsburg is located some distance from this boundary; approximately 220 km in the migra- tion route was along the river valleys. Using the cut- off point of 0.001, 16 of the total of 69 burials from the Bell Beaker period are distinguished as immi- grants. Since, in those individuals where only a tooth specimen was available for analysis, the respective isotopic ratio agrees with the isotopic characteristic of the burial site, these individuals were not con- sidered as mobile. There was, however, one excep- tion: The Bell Beaker child from Straubing in grave 1 (Table 3) has a Sr isotope ratio in tooth enamel of 0.71621 (no compact femoral bone was available). This child must have moved a substantial distance in the early years of its life. Thus, a total of 17 of the 69 Bell Beaker individuals, almost 25%, moved resi- dence to new geological regions during their life- times.

We also report a second cut-off value, the mean + 2 standard deviations of all bone 87Sr/s6Sr values, or 0.709041 f(2 x 0.000616). Bone values should repre- sent a reasonable estimate for long-term residents of the area. The bone mean + 2 S.D. value is 0.7103. This bone value is used as a cut-off point in the enamel 87Sr/86Sr data to distinguish immigrants. This value substantially exceeds the maximum *7Sr/86Sr value for soil samples from the project area (0.70992) and is a very conservative estimate of immigration. In addi- tion, this value falls in a natural break in the distribution of enamel ratios (Fig. 3), supporting its use as a cutoff point. 13 samples lie beyond the cut-off value of 0.7103, or 17.5% of the total number of enamel samples that were analyzed. Thus, our best

Mobility of Bell Beaker people, use of Sr isotopes

Table 3. Archaeological, anthropological and archaeometrical data

521

Site Grave Tooth ppm Tooth Bone ppm Bone Bone-Tooth Tooth-Bone

Age Sex Sr 87Sr/86Sr Sr “Sr/‘% Lab ref. Sr s7Sr/%r

Al 17112 Al 180/3 Au 1 Au 2 Au 3 Au 4 Au 5 Au 8 Au 9 Au 10 Au 13 Au 14 Au 15 Au 16 Au 17 Au 19 Au 20 Au 21 Au 22 Ir 1 Ir 3 Ir 4 Ir 6 Ir 7 Ir 9 II 10 Ir 14 Ir 16 Ir 20 Ir 21 Ir 22 Kti 278 Kti 332 Ku 335 Ku 338 Kii 349 Kii 372 La 2 La 3/l La 4 La 5 La 7 La La ; La 101 La 103 Ma 1 Ma 2 Ma 4 OS OS : OS 10 OS 21 OS 25 OS 28 OS 29 OS 30 PO 1 Str 1 str 4

str Str 178 Str 18 Tii Eo TiJ Eu We 3 We 4

Juvenile Adult Adult Adult Adult Adult Adult Adult Juvenile Adult Child Adult Juvenile Adult Adult Child

Child Adult Adult Adult Child Adult Child Adult Adult Adult Adult Adult Adult Adult Adult Adult Adult Adult Adult

Child Child Adult Adult Adult Child Adult Adult Adult Adult Adult Adult Adult Adult Adult Adult Adult Adult Adult Adult Adult Child Juvenile Adult Adult Adult Adult Juvenile Adult Child

Male Male Male Male Male Female Male Male Female Male

- Male Male Female Female

- Male

- Female Female Male Female Female

- Female Male Male Male Male Female Female Male

Male Male Male Female

- -

Female Female Female

- Female

- -

Male Male Female Male Male Female Male

Female Female Male Male

- -

Male Male

- Male Male Male

-

62 0.71001 63 0.70849

170 0.70864 98 0.70882

261 0.70826 142 0.70861 127 0.70866 150 0.70838 78 0.71169

133 0.71638 78 0.70840

113 0.70858 125 0.70842 189 0.70832 160 0.70853 96 0.70846

103 0.70837 70 0.70975

158 0.70868 60 0.71001

110 0.70955 91 0.70963

12 197 Ill 106 109 136 85 78 65 77

!z 43 61 70 54 49 51 99 47

302

:: 64

196

;: 50

256 100 42 55

118

:; 149 55

104

z 147

;: 68

0.70956 0.70955 0.7093 1 0.70932 0.71150 0.70973 0.70991 0.70964 0.70882 0.70886 0.70938 0.70892 0.70960 0.70951 0.70949 0.70944 0.71081 0.71124 0.70926 0.70990 0.10861 0.71108 0.71014 0.70923 0.70846 0.71122 0.70924 0.70986 0.70915 0.70928 0.70960 0.71077 0.70893 0.71060 0.71054 0.71624 0.70986 0.71006 0.70919 0.71061 0.70972 0.70964 0.70938 0.70917

128 0.71009 190 0.70962 303 0.70837 440 0.70806 368 0.70806 274 0.70821 296 0.70821 390 0.70814 451 0.70818 378 0.70825

372 0.70822 341 0.70826 306 0.70822 402 0.70831

376 0.70833

348

332

0.70858 0.71092 0.70952

252 0.70913

328 0.70932 294 0.70938 254 0.70914 276 0.70933 349 0.70922 281 0.70901 328 0.70929 227 0.70928 248 0.70879 281 0.70902 204 0.70925 227 0.70905 320 0.70866

219 0.70897 140 0.70957 174 0.70884

211 121 201 179 220 210 178 233 228 185 236 262 209 208 64

24: 237 225 194 225 215 255

0.70912 0.70978 0.70913 0.70871 0.70871 0.70899 0.70935 0.70918 0.78904 0.70911 0.70903 0.70904 0.7094s 0.70938 0.70998

0.70997 0.71008 0.71039 0.71001 0.70985 0.70978 0.70870

4 4 2

:

:

: 1 3 3 2 3 2 3 3 3 3 4 4 4

44 4 4 4 4 4 4 4 3

: 3 3

: 3 394 3 3 3 3

: 3

: 3 3 3 3

: 3 3

t 4 4

44 4 4

:

66 -0.00008 127 -0.00113 133 0.00027 342 0.00076 107 0.00020 132 0.00040 169 0.00045 240 0.00024 373 0.00350 245 0.00813

259 0.00036 216 0.00015 117 0.00810 242 0.00022

273 0.00005

190

222

0.00010 -0.08091

0.00003

252 -0.70913

131 O.ooO23 183 -0.ooOo7 148 0.00018 167 0.08217 213 0.00051 202 0.00090 250 0.00035 161 -0.00045 171 o.OoOO7 226 0.00036 112 -0.00032 184 0.00055 253 0.00085

171 0.00184 89 0.00168 15 0.00041

-92 -0.00045 76 0.00130

136 0.00101 114 0.00051 23 - 0.00026

128 o.OQ223 85 -0.00011

183 0.00068 -28 0.00011

85 0.00017 193 0.00057 207 0.00172 92 -0.00051 150 0.00122 33 0.00056

186 -0.00011 133 -0.00002 161 -0.00120 160 O.OQO60 78 -0.09013

137 -0.00014 171 0.00068

522 G. Grupe et al.

Table 3. (Continued)

Tooth Toot;rppm 87Sr,86Sr

Bone ppm Bone Bone-Tooth Tooth-Bone Site Grave Age Sex Sr 87Sr/86Sr Lab ref. Sr 87Sr/86Sr

We 4 Child - 68 0.70917 3 We 5 Juvenile Male 90 0.70888 266 0.70870 I 176 0.00018 We 10 Adult Male 70 0.70886 282 0.70867 3 212 0.00019 We 12 Child - 91 0.70913 3 We 13 Child - 80 0.70910 3 We 14 Adult Female 102 0.70868 322 0.70872 3 220 -0.00004 We 17 Adult Male 89 0.70958 306 0.70857 1 217 0.00102 We 18 Adult Male 79 0.70861 289 0.70905 3 210 -0.00044 We 19 Adult Male 57 0.71066 284 0.70885 3 227 0.00181 We A Adult Female 120 0.70992 368 0.70861 I,4 248 0.00131 We D Adult Female 131 0.71288 251 0.70891 1,4 121 0.00397

Average: 99 0.70967 266 0.70904 Maximum: 302 0.71638 451 0.71092 Minimum: 31 0.70826 64 0.70806

Lab ref no. 1: UW Madison, December 1992, NBS-987 =0.71020 (2SD of 0.00008; n=4). Old collectors. Lab ref no. 2: UW Madison, March 1994, NBS-987=0.71023 (2SD of 0.00010; n= 13). Old collectors. Lab ref no. 3: UW Madison, 1995, NBS-987 = 0.7 1026 (2SD of 0.00002; n = 100 +). New collectors. Lab refno. 4: German lab, NBS-987=0.71023 (f0.00001; n= 10). All data normalized to NBS-987 =0.71026.

Table 4. Number of analyzed Bell Beaker burials per cemetery and tooth/bone samples from the same individual

Cemetery Number of burials T/B pairs

Altdorf 2 2 Augsburg 17 14 Irlbach 12 9 K&zing-Bruck 6 6 Landau 9 6 Manching 3 3 Osterhofen 8 8 Pommelsbrunn 1 1 Straubing-oberau 5 4 Ttickelhausen 2 2 Weichering 10 7

Table 5. Age of Bell Beaker burials

Age Number of burials

Child Juvenile Adult Unknown

12 7

53 1

Table 6. Sex of Bell Beaker burials

Sex Number of burials

Male 38 Female 24 Unknown 13

estimate for the number of immigrants in the Bell Beaker burials from southern Bavaria ranges between 17.5 and 25%. More detailed analysis of the data also provides interesting information. Examination of the individual sites indicates a tendency for more migra- tion in the older part of the Bell Beaker period (Table 7). The larger sites of Irlbach, Augsburg, and Weichering are dated to the younger phase of the Bell Beaker period. The larger cemeteries of the younger phase contain more burials, 20-30 inhuma- tions, perhaps an indication of a more sedentary population.

Histogram

0 50 100 150 200 250 300 350 400 450 500

Bone Sr ppm

Histogram

6 IO

g 8 u 6

4 2 n

0 50 100 I50 200 250 300 350

Tooth Sr ppm Fig. 2. Histograms of Sr ppm for bone and tooth enamel.

Mobility of Bell Beaker people, use of Sr isotopes 523

500

450 ,Oo

400 ., 0 Ck

?? Au tooth 0 Au bone - cut-off * Soils - all teeth ?? all bones

0 , 0.708 0.709 0.710 0.711 0.712 0.713 0.714 0.715 0.716 0.717

8lSrl86Sr Fig. 3. Strontium isotope. ratios in all Bell Beaker buriah with the Augsburg site as a special example, plotted

against Sr ppm.

With regard to sex, females were somewhat more mobile than males. Some 62 of the skeletons could be sexed either anthropologically or archaeologically; 38 were males, and 24 were females. An equal number of males and females (8 each) were mobile using the 0.001 cutoff value. Thus, a higher proportion of females appear to be immigrants; this pattern is present at the individual sites as well.

The overall direction of migration for the Bell Beaker people, based on the Sr isotope data is from NE to SW. The next adjacent region to the SW is the southern alpine area, which lacks Bell Beaker sites. A southern origin is possible for the two La T&e Iron Age burials from Weichering.

Table 7. Sample size and immigrants at individual Bell Beaker sites

Site Number of

samples Number of immigrants

Percentage immigrants

Irlbach 12 2 16.7 Augsburg 14 2 14.3 Osterhofen 8 3 37.5 Altdorf 2 1 50.0 Landau 9 4 44.4 Straubing 5 2 40.0 Manching 1 33.3 Weichering : 2 33.3

Cut-off value of 0.001 is used to identify immigrants.

DISCUSSION

Since the skeletal morphology of the Bell Beaker skeletons is distinct from the earlier Neolithic people in the region of southern Bavaria, it could be assumed that the Bell Beaker people were indeed migrants into this area. However, morphology alone is not proof of migration since the underlying genetic controls of bone size and shape are still unknown. At present, Sr isotope analysis is the only means for a direct assessment of residence change during a lifetime capable of distinguishing migrant individuals from indigenous ones.

The proportion of migrant individuals in our samples lies between 17.5 and 25%. Does this represent a high or low rate of migration? The number of living individuals at a given burial site is calculated from life table data based on the number of dead encountered, using the formula

p Dxes =-+k,

t

where P = number of living individuals; D = number of excavated burials; e,” = average life expectancy at birth; t = time during which the burial site was in use; and k = correcting factor (Herrmann et al., 1990). This correction factor, k, equals 10% of D x ei/t and is based on historical data, considering that members of the population may have died and been buried at a different place. Thus, an average emigration rate of 10% is assumed. Although emigration and immigra- tion rates need not be identical, both figures should be balanced somehow in a given region as long as there is

524 G. Grupe et al.

an absence of indicators for gross population growth early childhood and the last years before death. If or decline. If this “rule of thumb” of 10% emigration values for both tooth and bone are similar, as is the also holds for the late Neolithic, the mobility of the case for 75% or more of the population that we Bell Beaker people with 17.5525% mobility was analyzed, no movement is signalled. We are unable to indeed very high. We should also note that the Sr determine, however, whether an individual moved isotope technique will only identify those individuals back and forth between areas during its lifetime, or moving between geologically distinct regions. Inter- whether an individual changed residence, but only regional movement will not be distinguished. In this within the same geological province. For these context, the Sr isotope technique underestimates the reasons, our results likely underestimate the amount amount of mobility in the population. It will be of residential mobility in the Bell Beaker period. We important to examine s7Sr/86Sr values in other conclude, therefore, that Bell Beaker people in south- populations to determine rates of migration in ern Bavaria were indeed highly mobile bearers of their prehistory. culture.

We can only roughly estimate the minimal distances traversed by some migrant individuals since a rela- tively high 87Sr/86Sr value in tooth enamel only indicates an origin NE of the Danube River but does not indicate how far from this geochemical boundary the individual was raised. Graves 9 and 10 at Augsburg contained two migrant individuals at the maximum distance from the granitic deposits north- east of the Danube. If those two individuals traveled along the rivers, first to the W and then to the S, the total distance involved was at least 220 km.

Acknowledgements-This research was supported in large part by the Deutsche Forschungsgemeinschaft to Gisela Grupe. Additional funding from the National Science Foundation to T. Douglas Price (BNS-8702731), to T. Douglas Price, James H. Burton, and Clark M. Johnson (BNS-9111680), and to Clark M. Johnson (EAR-9105966, EAR-9406684. and EAR-9304455). Samole oreoaration and laboratory work in Madison was done’in’fin~ fashion by Kathie Evans and Bill Middleton, in Munich by Dirk Weickmann.

Editorial Handling: Prof. P. Fritz.

For a pioneering population moving into an unknown region, it may have taken years or even generations to cover such a distance (Hassan, 1981). However, for migration into an already settled region, such as southern Bavaria in the late Neolithic, this distance of 220 km may have been covered in a few weeks or months. The hypothesis that this area was already well known is supported by evidence from Grave 9 at Augsburg, a migrant female who died at approximately 15 a of age. Her *‘Sr/?Sr enamel ratio of 0.71169 indicates an origin N of the Danube, whereas her 87Sr/86Sr bone ratio is 0.70818, which matches the local levels at Augsburg. This juvenile female must have made the journey during childhood. There is another case of mobility during childhood as well, Grave 1 from Straubing (Table 3), which also had a signature for granite/gneiss in the tooth enamel (0.71621). No bone sample was available from this individual, but local soil samples provided a value of 0.70966, indicating that the child was not born at the site.

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