refuse zone adjacent to structure 2-77.The second dates the upper surface ofthis zone and several cairns. The othernine dates are consonant, given statisti-cal probability. The earliest date may betoo early for Valdivia I, but the seconddate is in accord with those from anotherearly Valdivia site, Loma Alta. A periodaround 3300 B.C. seems plausible for theappearance of Valdivia on the Ecuador-ian Pacific coast.

After the identification of the originalthree carbon samples, the Real Alto car-bonized materials were reexamined forfaments of dense carbon similar to thecotyledon fragments in the three originalsamples. Another sample, CS 93, alsoexcavated in 1977, contained five suchfragments. Sixteen other firments werefound in samples from the Valdivia I,Valdivia III, Valdivia IV/V, and ValdiviaVI phases and nine fragments from asyet undated Valdivia features (4). Thissuggests that Canavalia was used duringValdivia I times and throughout the oc-cupation of Real Alto. The possibilitythat Canavalia plagiosperma was pres-ent at Real Alto as a domesticate andwas used as a food resource by theValdivians is thus supported.Other findings suggestive of the pres-

ence of agriculture during the Early For-mative of Ecuador include phytoliths(silica bodies deposited in the leaves ofcertain plant families) identifiable as amaize type, which occur as early asValdivia I at Real Alto and continuethroughout the later Valdivia and Ma-chalilla occupation (3, 4). Beginning inValdivia Ill, phytoliths identified as Can-naceae, the family of the edible cultivat-ed achira Canna edulis, also occur.Since there are no native Cannaceae onthe coastal plain of southwestern Ecua-dor, the introduction of cultivated Cannais a possibility.-The prehistoric occurrence of the

South American domesticated Canava-lia plagiosperma is known for coastalPeru beginning with the Late Preceramic(about 2500 to 1800 B.C.). Canavaliawas recovered by Bird at Huaca Prieta incoastal Peru (7). Connections betweenHuaca Prieta and Valdivia have beensuggested (1). The presence of the wildand possibly ancestral forms of C. mari-tima and C. brasiliensis in western Ecua-dor and of C. maritima extending intoextreme northern Peru (8) indicates thatthis region was probably a site of earlyCanavalia domestication. The Real Altodata give chronological priority to anorthern Ecuadorian origin.One additional point is significant.

Canavalia species are confined to humidareas. Irrigation in some form is neces-

sary for growing the domesticated spe-cies in areas with short rainy seasons.Since the southwesternmost part of Ec-uador is an area ofmnal rainfall witha short rainy season, the presence ofprehistoric Canavalia at Real Alto indi-cates a wetter area of origin for Valdivia,possibly the Colonche hills and the Gua-yas Basin of Ecuador.

JONATHAN E. DAMPDepartment ofArchaeology,University of Calgary,Alberta 72N 1N4, Canada

DEBORAH M. PEARSALLDepartment ofAnthropology,American Archaeology Division,University of Missouri, Columbia 65211

LAWRENCE T. KAPLANDepartment ofBiology, University ofMassachusetts, Boston 02125

addresses the causes of climatic change.

The dry snow facies of the continentalice sheets and ice caps contain particu-late material and isotopic species thatprovide information about the physicalproperties of the atmosphere at the timeof precipitation formation and deposi-tion. These data must be interpretedcautiously, as the complex relationshipbetween particles (and gases) in the at-mosphere and those in the associatedprecipitation is poorly understood (1).Nevertheless, a substantial increase inthe quantity of material suspended in theglobal atmosphere should be recordedwithin the particle stratigraphy of thepolar ice sheets.The concentration and size distribu-

tion of insoluble particles within firn andice cores are determined by the Coultertechnique conducted within a class 100clean room (2). Thus far, three ice coresencompassing at least the end of the lastmajor glaciation (correlative with theLate Wisconsin or Wurm stage) and thepostglacial (Holocene) strata have beenanalyzed for microparticle concentrationand the 180/160 ratio (8180), a paleocli-matic indicator revealing the glacial-

Rhrem Nesad Note1. E. Lanning, Peru Before the Incas (Prentice-

Hall, Englewood Cliffs, N.J., 1967); D. Lathrap,Mus. Texas Tech. Univ. Spec. Publ. 7, 115(1974).

2. D. Lathrap, D. Collier, H. Chandra, AncientEcuador: Culture, Clay, and Creativity 3000-300B.C. (Field Museum of Natural History, Chicago,1975); J. Marcos, Tejidos hechos en telar en uncontexto Valdivia tardfo (Casa de la CulturaEcuatoriana, Guayaquit, 1973); C. Zevallos, Laagricultura en el formativo temprano del Ecua-dor (cultura Valdivia) (Casa de la Cultura Ecua-toriana, Guayaquil, 1966-1971); , WY. C.Galinat, D. W. Lathrap, E. R. Leng, J. G.Marcos, K. M. Klumpp, Science 196, 385 (1977).

3. D. M. Pearsall, Science 199, 177 (1978).4. , thesis, Department of Anthropology,

University of Illinois (1979).5. J. Damp, thesis, Department of Archaeology,

University of Calgary (1979).6. See measurements in the following: 0. Berglund-

Bricher and H. Bricher, Econ. Bot. 30, 257(1976); H. Gentry, ibid. 23, 55 (1969); L. Kaplanand R. MacNeish, Bot. MAs. Leafl. Harv. Univ.19, 33 (1960); J. Purseglove, Tropical Crops:Dicotykdons (Haisted, New York, 1972).

7. J. Bird, Am. Antiq. 13, 21 (1948).8. J. Sauer and L. Kaplan, ibid. 34, 419 (1969).29 January 1981

postglacial transition. These three coresare those from Byrd Station, Antarctica(2164 m) (3, 4); from Camp Century,Greenland (1387 m) (5, 6); and fromDome C, Antarctica (905 m) (7-9).The examination of individual parti-

cles by light microscopy and scanningelectron microscopy coupled with ele-mental analysis by an x-ray energy-dis-persive system (XEDS) is a routine partof the microparticle analysis procedure(10). The Camp Century core particlesare composed primarily of clay minerals(5, 11), whereas both clay fragments andvolcanic glasses were found in the Byrdcore (2). These volcanic glasses aremuch more abundant in the late glacialsections of the Byrd core than in theoverlying Holocene sections. The XEDSanalyses are conducted only for particleswith diameters greater than 5 p,m, as theanalysis of smaller particles is unreliable.The particles in the Dome C core fall

into two distinct classes according tosize. The smaller particles (with diame-ters < 2 pSm) are more abundant by threeor more orders of magnitude. The lessabundant, larger particles (diameters be-

SCIENCE, VOL. 212, 15 MAY 1981

Microparticle Concentration Variations Linked withClimatic Change: Evidence from Polar Ice Cores

Abstract. The microparticle concentrations in three deep ice cores reveal a

substantial increase in the concentration of insoluble particles in the globalatmosphere during the latter part of the last mqjor glaciation. The ratio of theaverage particle concentration in the late glacial strata to that in the Holocene stratais 611 for the core from Dome C, Antarctica, 311 for the core from Byrd Station,Antarctica, and 1211 for the core from Camp Century, Greenland. Whether thistemporal correlation between increased atmospheric particle load and the lowersurface temperatures is directly causal is unknown; however, the variations in thesetwo parameters must be satisfactorily resolved in any successful hypothesis that

0036-8075/81/0A5150812$00.50/0 Copyright © 1981 AAAS812

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tween 60 and 80 ,um) are predominantlyvolcanic glass fragments which exhibit amuch greater frequency of occurrence insections below 500 m in this core. Thoseglasses that have been analyzed with theelectron microprobe are nearly identicalin morphology and chemistry to thosefound within several ash bands in theByrd core and whose source has beensuggested to be Mount Takahe, Antarcti-ca (12).The smallest fragments in the Dome C

core are too small for quantitative chemi-cal analysis and do not exhibit a distin-guishable morphology. Their source orsources are unidentified. This insolublematerial may represent a diverse mixturecomposed primarily of global strato-spheric material brought to the surfaceby the descending motions over the Ant-arctic Plateau (13) and a smaller compo-nent of tropospheric material transport-ed by cyclonic disturbances which peri-odically penetrate the plateau region.The 905-m core from Dome C, Antarc-

tica (74°39'S, 124°10'E, 3240 m abovesea level), was drilled as part of theInternational Antarctic GlaciologicalProgram (14), and 51 sections providedby the French were analyzed for micro-particle concentration and size distribu-tion. The microparticle analysis of 5367samples representing these 51 sections(averaging 0.76 m in length) comprisesthe most detailed microparticle recordfrom any deep core. The average samplesize of 0.0067 m of ice coupled with theannual accumulation of 0.035 m of ice(15) yields a resolution of 5.5 samples peraccumulation year.Accurate dating of ice cores is essen-

tial for interpreting any proxy data ob-tained from ice cores as well as forcomparison of the core record with exist-ing records. Dating of strata older than100 years is a particular problem on thecentral Antarctic Plateau where accumu-lation rates are low (< 0.1 Im/year) (16)and where the deepest cores, and hencethe longest records, will be obtained.Cyclical variations in insoluble micro-particle concentrations in the 101-mSouth Pole core were found to be annualfeatures (10). The detailed analysis of theDome C core sections revealed similarcyclical variations in particle concentra-tion (Fig. 1). A Dome C pit study (8) andthe net accumulation rates deduced fromthe microparticle variations in each coresection (8, 9) support the annual charac-ter of these microparticle features.

Figure 1 presents the concentrationsof small particles (0.63 ,um c diameter< 0.80 ,um) (C) for five sections from thepostglacial strata and three sections fromthe glacial strata of the Dome C core,15 MAY 1981

respectively, and the average verticallayer separation (ai) in water equivalentfor each section. These estimates are ingood agreement with the current esti-mate of net annual surface accumulation,0.035 m of ice per year (density = 920kg/m3) or 0.032 m of water per year (15);these results suggest that these particleconcentration peaks are annual. Theproblems that plague all stratigraphic in-terpretations (for example, missingyears) are present here, but the solutionmust await the absolute dating of icestrata older than 100 years.These annual features can be used to

construct a relative time scale for theDome C core as detailed in (8, 9). Themaximum estimate for the age at thebottom of this core is 30,000 years,which is slightly older than the 27,000

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years derived from Nye's model dis-cussed in (7). Using an entirely differentapproach, Lorius et al. (7) estimated theage at the bottom to be 32,000 years.This older age was obtained by assuminglower accumulation rates at core depthsgreater than 381 m. On the basis of 51sections of the Dome C core analyzed,no consistent or substantial reduction innet surface accumulation exists (8, 9).

In the Dome C core the largest in-creases in C are temporally correlatedwith the most negative 8180 measure-ments (lowest temperatures). The Byrdand Camp Century cores also exhibitvery substantial increases in particleconcentration in association with morenegative 8180 values representing thelast major glaciation (Fig. 2). The aver-age concentration of particles (diameters

is 8-

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Fig. 1. Concentration of particles with diameters greater than or equal to 0.63 p.m and less than0.80 p.m for five sections from the Holocene (upper 500 m) (left) and for three sections from thelate glacial portion (lower 400 m) (right) of the Dome C, Antarctica, ice core; * indicates annualfeatures, ? indicates questionable features, and A indicates values exceeding the ordinate scale.At the lower left is listed the vertical layer separation (at) in meters of water equivalent for eachof the eight sections illustrated.

813

I

-0.6 ,um) in all sections of the CampCentury core is 7.8 times that in the Byrdcore and 5.7 times that in the Dome Ccore. This large concentration in theCamp Century core reflects the exten-sive particulate source areas in theNorthern Hemisphere.To obtain an estimate of past back-

ground levels of insoluble particles forcomparison with 8180 measurements,the average number of particles withdiameters between 0.6 and 0.8 ,um in thecleanest 10 percent of all samples (CI0) iscalculated for each core section and il-lustrated in Fig. 2b. A statistical exami-nation of the relationship between 8180and CI0 (9) indicates that the two varia-bles are not independent at the 99.9percent confidence level. Nevertheless,a cause-and-effect relationship cannot beassumed as the variation in both particle

a

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Dome C,East Antarctica

concentration and 8180 could be pro-duced by some as yet undetermined forc-ing function.The ratio of the average particle con-

centration in sections representing theend of the last glacial to the averageconcentration for postglacial sections(Fig. 2a) is 6/1 for the Dome C core, 3/1for the Byrd core, and 12/1 for the CampCentury core. This increase is probablydue to a corresponding increase in atmo-spheric particle loading, a reduction inannual net accumulation, or some com-bination of these factors. In each corethe particle concentration falls off rapid-ly during the transition into the Holocene(Fig. 2). Either the net accumulationregime at each site was rapidly altered,diluting the particles, or the particlesource was rapidly diminished.The increase in C in the late glacial

articles > 0.6 Aim In diameter(13)

10 30 s00 A

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800

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Hw

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Fig. 2. (a) The average concentration of particles with diameters greater or equal to 0.6 p.m forall samples in each section; (b) the concentration of particles with diameters between 0.6 and 0.8p.m in the cleanest 10 percent of the samples in each section of three deep ice coresencompassing the end of the last major glaciation. The transition into the Holocene (designatedby HIW) is based upon the 8180 record for each of the cores as compiled by Lorius et al. (7) forthe Dome C core, Epstein et al. (4) for the Byrd Station core, and Dansgaard et al. (6) for theCamp Century core. To accommodate the high particle concentrations in the Camp Centurycore, the abscissa scale is increased by one order of magnitude.

814

sections of each core exceeds that ex-pected merely from a reduction in netaccumulation alone. In the Dome C core,for example, the sixfold increase in theaverage particle concentration for sec-tions below 500 m far exceeds any con-centration resulting from a 30 to 40 per-cent reduction in net -accumulation as issuggested to have occurred (7). The ac-cumulation data discussed above (seealso Fig. 1) and presented in detail in (8,9) exhibit little variation within the 51sections analyzed.On the basis of these data, it is not

likely that reduced accumulation can ac-count for the increase in particles. It ismore probable that a substantial quantityof additional material was added to theglobal atmosphere near the end of thelast glaciation. Whether the material isvolcanic or loess has yet to be deter-mined. Nevertheless, the relationshipbetween this increase in atmosphericparticles and the reduction of global tem-peratures must be resolved satisfactorilyin any successful hypothesis that ad-dresses the causes of climatic change.

L. G. THOMPSONE. MOSLEY-THOMPSON

Institute of Polar Studies,Ohio State University,Columbus 43210

References and Notes1. C. E. Junge, in Proceedings of the Grenoble

Symposium on Isotopes and Impurities in Snowand Ice (Publication 118, International Associa-tion of Hydrological Sciences-Association In-ternationale des Sciences Hydrologiques, Paris,1977), pp. 63-77.

2. L. G. Thompson, Ohio State Univ. Inst. PolaraStud. Rep. 64 (1977).3. __ , W. L. Hamilton, C. Bull, J. Glaciol. 14,

72 (1975).4. S. Epstein, R. P. Sharp, A. J. Gow, Science 168,

1570 (1970).5. L. G. Thompson, in Proceedings of the Greno-

ble Symposium on Isotopes and Impurities inSnow and Ice (Publication 118, InternationalAssociation of Hydrological Sciences-Associa-tion Internationale des Sciences Hydrologiques,Paris, 1977), pp. 351-364.

6. W. Dansgaard, S. J. Johnsen, H. B. Clausen, C.C. Langway, Jr., in Late Cenozoic GlacialAges, K. K. Turekian, Ed. (Yale Univ. Press,New Haven, Conn., 1971), pp. 37-56.

7. C. Lorius, L. Merlivat, J. Jouzel, M. Pourchet,Nature (London) 280, 644 (1979).

8. L. G. Thompson, E. Mosley-Thompson, J. R.Petit, in Proceedings ofan International Sympo-sium on Sea Level, Ice Sheets, and ClimaticChange (International Union of Geodesy andGeophysics, Canberra, Australia, in press).

9. L. G. Thompson and E. Mosley-Thompson,Palaeogeogr. Palaeoclimatol. Palaeoecol., inpress.

10. E. M. Thompson, thesis, Ohio State University(1979).

11. M. Kumai, in Proceedings of the GrenobleSymposium on Isotopes and Impurities in Snowand Ice (Publication 118, International Associa-tion of Hydrological Sciences-Association In-ternationale des Sciences Hydrologiques, Paris,1977), pp. 341-349.

12. P. R. Kyle, P. A. Jezek, E. Mosley-Thompson,L. G. Thompson, in Proceedings of an Interna-tional Symposium on Volcanism and Climate(International Union of Geodesy and Geophys-ics, Canberra, Australia, in press).

13. E. R. Reiter, Atmospheric Transport Processes,part 2, Chemical Tracers (Atomic Energy Com-mission, Oak Ridge, Tenn., 1971).

14. C. Lorius and D. Donnou, Courr. Centre Natl.Rech. Sci. 30 (1978).

SCIENCE, VOL. 212

Particles 0.6 to 0.8,um in diameter(103)2 6

0 ..

Byrd Station,West

400 Antarctica 4

8001

1200

1600

2000

t

A

I

I

15. J. R. Petit, J. Jouzel, M. Pourchet, L. Merlivat, vided by the Centre National de la Recherchein Proceedings of an International Symposium Scientifique, Laboratoire de Glaciologie. Weon Progress in Meteorology (International thank C. Lorius and J. R. Petit for their cooper-Union of Geodesy and Geophysics, Canberra, ation and valuable discussions. This work wasAustralia, in press). supported by NSF grant DPP 7719371-A02.

16. C. Bull, in Research in the Antarctic, L. 0. Contribution 402 of the Institute of Polar Stud-Quam, Ed. (AAAS, Washington, D.C., 1971), ies, Ohio State University.pp. 367-421.

17. Sections of the Dome C core were kindly pro- 20 March 1980; revised 6 February 1981

The Prolactin Gene Is Located on Chromosome 6 in Humans

Abstract. The gene for prolactin has been located on chromosome 6 in humans.DNA fragments of4.8 and 4.0 kilobases containing prolactin gene sequences wereidentified in human genomic DNA, whereas DNA fragments of 7.4, 3.6, and 3.3kilobases containing prolactin gene sequences werefound in mouse cells. In somaticcell hybrids of human and mouse cells the 7.4-, 3.6-, and 3.3-kilobase mousefragments were always present, whereas the 4.8- and 4.0-kilobase human fragmentswere only present when human chromosome 6 was also present. We conclude that theprolactin gene resides on chromosome 6, a different locationfrom those ofthe genesforthe related hormones chorionic somatomammotropin and growth hormone.

The polypeptide hormones growthhormone, chorionic somatomammotro-pin (placental lactogen), and prolactinbelong to a common family (1, 2). Hu-man growth hormone and chorionic so-matomammotropin are composed of 191amino acid residues and are closely relat-ed, with about 85 percent homology intheir amino acid sequences (3, 4). Hu-man prolactin is composed of 199 aminoacid residues and is more distantly relat-ed, having only 26 percent homologywith human growth hormone and 27 per-cent homology with chorionic somato-mammotropin (4). The human growth hor-mone and human chorionic somatomam-motropin messenger RNA's (mRNA's)have 92 percent homology, whereas thehuman prolactin mRNA has 42 percenthomology with human growth hormoneand 41 percent homology with chorionicsomatomammotropin sequences (4-6).The genes coding for these three poly-

peptide hormones are believed to haveoriginated from a common ancestralgene by duplication. Prolactin is thoughtto be the d1dest' member of this group(4, 7, 8). While the human growth hor-mone, chorionic somatomammotropin,and a third growth hormone-like genehave been located on chromosome 17(9), the chromosome localization of thehuman prolactin gene (pro was notknown.We report here that the prolactin gene

is not on the same chromosome as thegrowth hormone gene, the chorionic so-matomammotropin gene, and the growthhormone-like gene; rather it is locatedon chromosome 6 in humans. Somaticcell hybrids of human and mouse cellscontaining all the mouse chromosomesbut lacking certain human chromosomeshave been used to determine this chro-mosome localization. These cell hybridswere constructed, maintained, and ana-

lyzed as previously described (10).Large-molecular-weight DNA was iso-

lated from cultured mouse cells, humancells, and human-mouse cell hybrids andwas digested with the restriction endonu-clease Eco RI. The digested fragmentswere then separated-by electrophoresison agarose gels and transferred to nitro-cellulose filters (9, 11). Restriction frag-ments containing the prolactin geneswere analyzed by hybridizing the filterswith labeled prolactin complementaryDNA (cDNA) probes. The cloning ofDNA complementary to both rat andhuman prolactin mRNA has been report-ed (4, 12). 32P-Labeled prolactin probeswere prepared by nick translation or byrandom priming with calf thymus DNAprimers (9, 11). Specific activities greaterthan 108 cpm/,ug were routinely ob-tained. The hybridization of these probeswith filters containing human, mouse, orhuman-mouse cell hybrid Eco RI restric-tion fragments and the washing of the fil-ters to remove nonspecifically bound probewere performed as described (9, 11).

In the control mouse line, the rat pro-lactin probe hybridized with three frag-ments of 7.4, 3.6, and 3.3 kb (Fig. 1,channel i). The rat prolactin probe didnot cross-hybridize with human DNAunder these hybridization and washingconditions (Fig. 1, channel j). Similarly,the human prolactin probe did not cross-hybridize with mouse DNA sequences(Fig. 1, channel a). In the control humancell line and in all the human cell linesused in this investigation, the humanprolactin probe hybridized with two frag-ments of 4.8 and 4.0 kb (Fig. 1, channelb).The mouse 7.4-, 3.6-, and 3.3-kb DNA

fragments were present in all cell hy-brids, while the human 4.8- and 4.0-kb

Human probe Rat probe

Fig. 1. Analysis of human and mouse prolactin DNA sequences present in EcoRI restriction digests of mouse, human, and human-mouse cell hybrid DNA.Isolation, digestion, and transfer of DNA to filters and hybridization were asdescribed (1, 11). Labeled DNA bands were detected by exposing the filters tox-ray film for 2 to 10 days in the presence of an intensifying screen (DupontLightning Plus). Channels a through h were hybridized with human prolactinprobe, while channels i through p were hybridized with rat probe. Prolactinhybridization patterns are shown for (channels a and i) mouse RAG cells;(channels b and j) human T cell lymphoblasts; (channels c and k) hybrid ALR-2;(channels d and 1) hybrid TSL-2; (channels e and m) hybrid TSL-5; (channels fand n) hybrid TSL-6; (channels g and o) hybrid WIL-3; and (channels h and p)hybrid WIL-6. Fragments of Hind 111-digested lambda phage DNA (NewEngland Biolabs) were used as markers for molecular size. Hybrids ALR-2,TSL-2, and WIL-6 contained the human prolactin DNA sequences.

SCIENCE, VOL. 212, 15 MAY 1981

I I I I I I I I I I I I I I I Ia b c d e f g h i j k l m n o p

0036-8075/81/0515-0815$00.50/0 Copyright 1981 AAAS 815

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