17 March 1972Vol. 175, No. 4027

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LETTERS Mercury Residues: A. C. Kolbye, Jr.; Objectives of Cancer Research: G. E. Moore;A. T. Chari; Captive Audience: A. B. Pardee; Fusion by 1990?: R. C. Axtmann;C. Hosmer; "Necessity or Chance": A. J. MacInnis .... ..

Limits to Growth

ARTICLES Gosses Bluff Impact Structure, Australia: D. J. Milton et al....................Classic to Postclassic in Highland Central Mexico: D. E. Dumond and F. Muller ...

Costs, Benefits, Effectiveness: Challenge to Educational Technology: L. P. Grayson

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NEWS AND COMMENT

RESEARCH NEWS

BOOK REVIEWS

Academic Freedom at Stanford: Lessons of the Franklin CaseDivision of Biologics Standards: The Boat That Never Rocked ......

Cancer Radiation Therapy: Potential for High Energy Physics .....

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Avian Biology, reviewed by A. Keast; Geography of Domestication, R. I. Ford;Mountain Sheep, R. M. F. S. Sadleir; Numerical Weather Prediction, Y. Kurihara;Bioinorganic Chemistry, A. Hooper; Aspects of Terpenoid Chemistry andBiochemistry and Terpenoids and Steroids, R. A. Bernihard; Changing Synthesesin Development, P. J. Stambrook; Neurotransmitter-Receptor Interactions,D. H. Jenkinson and L. T. Potter; Vertebrate Paleozoology, L. Van Valen;Books Received ..................... ............... .. 1233

REPORTS Archeological Excavations in Jalisco, Mexico: B. Bell ... ......... ...

Electrical Generation of Natural Aerosols from Vegetation: B. R. Fish ... .. .. ...

Plastics on the Sargasso Sea Surface: E. J. Carpenter and K. L. Smith, Jr ..

Matanchen Complex: New Radiocarbon Dates on Early Coastal Adaptation in WestMexico: J. B. Mountjoy, R. E. Taylor, L. H. Feldman ............................

Apollo 14 Active Seismic Experiment: J. S. Watkins and R. L. Kovach ..... ......

Carbon Isotopic Studies of Organic Matter in Precambrian Rocks: D. Z. Oehler,J. W. Schopf, K. A. Kvenvolden ...............................................

::CP:w:IRESIDENTS AND

SECT:IO.N SECRtETARIESMATHEMATICSJofhn W. TulceyF. A. Ficken

PSYCHOLOGY (1)Dale B. HarrisWilliam D. Gervey

PHARMACEUTICAL SCIENCES (Np)Linwoo F. TiceJohn Autian

ALASKA DIVISIONordon Harrison Irma DuncanPresident Executive Secrtary

PHYSICS (B) CHEMISTRY (C)Herbert Friedman Martin PaulRolf M. Sinclair Leo Schubert

SOCIAL AND ECONOMIC SCIENCES (K)James S. ColemanHarvey Sapoisky

AGRICULTURE (0) INDUSTRIRoy L. Lovvorn Jacob E.Michael A. Farrell Jordan D.

PACIFIC DIVISIONRoy A. Young Robert C. MillerPresident Secretary

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ASTRONOMY (D)George B. FieldArlo U. Landolt

HISTORY AND PHILOSOPHY OF SCIENCE (kEverett MendelsohnRaymond J. :Seeger

[AL SCIENCE (P) EDUCATION (Q)Goldman Lloyd K. JohnsonLewis Phillip Fordyce

SOUTHWESTERN AND ROCKY MOUNTAIN DVISIONJohn R. Lecher Marlowe G. AndersonPresident Executive Segretry

EDITORIAL

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Decreased Concentration of Phenacetin in Plasma of Cigarette Smokers:E. J. Pantuck, R. Kuntzman, A. H. Conney ......................................

An Eocene Hystricognathous Rodent from Texas: Its Significance in Interpretationsof Continental Drift: A. E. Wood .............................................

Nerve Growth Factor: Stimulation of Regenerative Growth of Central NoradrenergicNeurons: A Bjorklund and U. Stenevi .........................................

The Hill Plot and the Energy of Interaction in Hemogloblin: H. A. Saroff andA. P. Minton ...............................................................

Rabies Virus in Nasal Mucosa of Naturally Infected Bats: D. G. Constantine,R. W. Emmons, J. D. Woodie .................................................

Paraoxon: Effects on Rat Brain Cholinesterase and on Growth Hormone and Prolactinof Pituitary: G. Cehovic, W-D. Dettbarn, F. Welsch ..............................

Predation of Schistosomiasis Vector Snails by Ostracoda (Crustacea):1. G. Sohn and L. S. Kornicker ...............................................

Homology between Nucleic Acids of Blue-Green Algae and Chloroplasts ofEuglena gracilis: G. H. Pigott and N. G. Carr . ..............................

Activities of Sodium and Potassium Ions in Epithelial Cells of Small Intestine:C. 0. Lee and W. McD. Armstrong ............................................

Messenger RNA Structure: Compatibility of Hairpin Loops with Protein Sequence:H. B. White III, B. E. Laux, D. Dennis .......................................

Iodine Metabolism: Preferential Renal Excretion of Iodide Derived fromTriiodothyronine Deiodination: S. Shimoda and M. A. Greer .....................

Fluorescent Banding Patterns of Rat Chromosomes in Normal Cells and PrimaryHepatocellular Carcinomas: S. R. Wolman, T. F. Phillips, F. F. Becker ... ..

6,7-Dihydroxytetrahydroisoquinoline: Uptake and Storage by PeripheralSympathetic Nerve of the Rat: G. Cohen, C. Mytilineau, R. E. Barrett ...

Coexistence of Two Asexual Strains on a Single Resource: B. R. Levin .................

Electron Microscopic Evidence for Plasmodesmata in Dicotyletonous Guard Cells:1. E. Pallas, Jr., and H. H. Mollenhauer ........................................

White-Noise Analysis of a Neuron Chain: An Application of the Wiener Theory:P. Z. Marmarelis and K. Naka .................................................

Technical Comments: Sulfur Mobilization as a Result of Fossil Fuel Combustion:J. P. Friend; K. K. Bertine and E. D. Goldberg; An Improved TreadingDevice for Tethered Insects: J. S. Carrel ........................................

MEETINGS Prostaglandins in Fertility Control: S. Bergstrom et al.; Forthcoming Events

WARD H. GOODENOUGH DANIEL P. MOYNIHAN WILLIAM T. GOLDEN WILLIAM BEVANCARYL P. HASKINS PHYLLIS V. PARKINS Treasurer Executive Officer

GEOLOGY AND GEOGRAPHY (E) BIOLOGICAL SCIENCES (FG) ANTHROPOLOGY (H)Frank C. Whitmore Ian Sussex Richard N. AdaAmsWilliam E. Benson Richard J: Goss Anthony LeedsENGINIEERING (M) MEDICAL SCIENCES (N) DENTISTRY (N4d)Newman A. Hall Robert W. Berliner Joseph L. Hen:ryRaytor L. Duncombe F. Douglas Lawrason Sholom PearlmanINFORMAtION AND STATISTICS (U) ATMOSPHERIC AND HYDROSPHERICCOMMUNICATION (1) W. Duane Evans SCIENCES W).Andrew A. Aimnes E-ra Glaser John A. htKnauss

Sctt Ada Ms Louis J. Battan

COVER

Flat, molded figurines with forward-jut-ting feet and prominent teeth (often styl-ishly mutilated) were made around A.D.800 in highland central Mexico. Thisfigurine was excavated in 1969 at theCerro de Xochitecatl, Tlaxcala, by BodoSpranz, under the auspices of the Deut-sche Forschungsgemeinschaft (actual size,about 20 centimeters high). See page1208. [Don E. Dumond, University ofOregon, Eugene]

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17 March 1972, Volume 175, Number 4027 SCIENCE

AMERICAN ASSOCIATION FORTHE ADVANCEMENT OF SCIENCE

Science serves its readers as a forum for thepresentation and discussion of important issuesrelated to the advancement of science, includingthe presentation of minority or conflicting pointsof view, rather than by publishing only materialon which a consensus has been reached. Accord-ingly, all articles published in Science-includingeditorials, news and comment, and book reviews-are signed and reflect the individual views of theauthors and not official points of view adopted bythe AAAS or the institutions with which the authorsare affiliated.

Editorial Board

1972ALFRED BROWNJAMES F. CROWTHOMAS KUHNELLIOTr W. MONTROLL

FRANK PRESSFRANK W. PUTNAMWALTER 0. ROBERTS

1973

H. S. GUTOWSKYARTHUR D. HASLERRUDOLF KOMPFNERDANIEL E. KOSHLAND, JR.

GARDNER LINDZEYRAYMOND H. THOMPSONEDWARD 0. WILSON

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Limits to GrowthThe public and its leaders are now aware of and rightly concerned

about the unpleasant potential consequences of overexuberant growth.Small wonder, then, that a 1-day symposium on the "Limits to Growth"held at the Woodrow Wilson Center in Washington on 2 March shoulddraw an attentive audience that included senators, ambassadors, and acabinet officer, as well as numerous representatives of the press, radio,and television.The principal speaker was Dennis Meadows, who has headed a study

group at Massachusetts Institute of Technology. This group has usedhigh-speed computers in an attempt to examine the interacting conse-quences of continued exponential growth of population, food production,industrialization, pollution, and consumption of nonrenewable natural re-sources. Meadows' major conclusion is the perhaps obvious one that, ifmankind continues to indulge at current rates in various forms of ex-ponential growth, calamities will occur in about 50 years.As a pioneering effort to evaluate a complex web of interactions the

study, and a popular book* based on it, is likely to have considerableimpact. The book is to be translated into half a dozen languages anddistributed broadly. The approach, though, has defects.

Responding to the allure of tackling a truly big problem, the studygroup has attempted to treat the entire Earth as a single system. In orderto limit the number of variables, they chose to aggregate variables on aglobal basis. Thus the population growth of all the world is taken as asingle variable, although the growth rates in various countries and regionsdiffer by a factor of 6 or greater. An even less defensible aggregationof variables is subsumed under pollution. Here an attempt is made tolump together the many components of solid, liquid, and gaseous pollu-tion, even though each differs in nuisance or toxic characteristics.

Enthusiasts can easily lose sight of the limitations of computers. Inthis study, data from the past are used as a basis for predicting the future,but such data are far more relevant to the past than to the future. Thecomputer is unaware of changing human behavior. Concern about thepopulation explosion and such matters as pollution has already had pro-found effects. Recently released figures show that the rate of growth ofpopulation in this country has been slowing. The rate of increase of im-portant polluting chemicals has been slowed, stopped, or is even decreas-ing. Important segments of the middle and upper-middle classes aretalking of a future "no growth" society.The study also does not adequately take into account ingenuity with

respect to natural resourcefs. Current technology is based on the avail-ability of certain raw materials, such as copper and natural gas. Asthese resources become scarce, technology will change and, for example,aluminum will be used as a oonductor, while methane will be obtainedfrom coal.The concept of Earth as a closed system is an appealing one, and

in some respects it is valid. We all share the oxygen of the atmosphereand must be concerned with changes in its carbon dioxide content. How-ever, much of pollution is local or regional in its effects. The same istrue with respect to population. Growth of population exacerbate:d byconcentration in urban centers is a bad enough problem in the UnitedStates. It is a far more serious and potentially catastrophic phenomenonin the so-called lesser developed countries.A member of the audience at the recent symposium privately re-

minded us that, although Meadows predicts hell in 50 years, hell is al-ready present on Earth in places such as Calcutta.-PHILIP H. ABELSON* D. H. Meadows, D. L. Meadows, J. Randers, W. W. Behrens III, The Limits to Growth,a report for the Club of Rome's Project on the Predicament of Mankind (Potomac Associ-ates-Universe Books, New York, 1972).