tive, is how best to elucidate microbial function—that is, how they make their liv- ing. No one technique is yet sufficiently well developed to do this; however, func- tional gene microarray systems, which look for expression of genes coding for enzymes inv olved in specif ic functions, are cur rently under development (13). An associated challenge is to determine the role of community microbial activity in shaping geochemical consequences. Geochemical interest in microbial activity is often restricted to a single metabolic function with a relevant geochemical con- sequence, such as metal sequestration (5, 7 ). However, the microbe responsible for that geochemical impact likely exists with- in a microbial community or consortium (12). The by-products from one organism’ s metabolic pathway are the nutrients of the next strain. Both the series of metabolic re- actants and products associated with a mi- crobial community, and the reaction ener- getics involved, are therefore likely to dif- fer from one location to the next. Thus, even though commonality of metabolic pathways ensures widespread occurrence of certain microbially driven geochemical processes in different envi- ronments, variability in microbial consor- tia and microgeochemical conditions will selectivel y ref ine that geochemical impact. In doing so, they may create community- specific microbial fingerprints on geo- chemical processes. Microbial growth and activity can only proceed through inputs of energy , and are thus constrained geochemically to reac- tions that are thermodynamically feasible. High-resolution analytical tools for geo- chemistry and culture-independent molec- ular microbial techniques have yielded ex- citing insights. Today, microbial activity is viewed to pla y an important—and quantif i- able—role in aqueous geochemistry. New molecular techniques for evaluating micro- bial functional activit y will provide ke y in- formation on how microbes engineer geo- chemical processes, and how they, in turn, are constrained by the geochemical world in which they find themselves. Systematic examinations of the links between genome and geochemistry will ex- plore gene expression (that is, function) and determine reaction kinetics of micro- bial communities growing under differing geochemical and physical conditions ( 14). Such studies will provide microbial finger- prints for important geochemical processes under microbial control. Moreover, such studies should help to quantify the micro- bial influence on important aqueous geo- chemical processes, determine the linked controls for these key processes, and show how feedback between microbial ecology and geochemical conditions influences the geochemical outcomes. References 1. K. T ak ai , T. Komat s u, F. I na ga ki , K . H or ik os hi , Appl. Environ. Microbiol. 67, 3618 ( 2001). 2. P. L. Bond, S. P. S mriga , J. F. Banfi eld , Appl. Environ. Microbiol. 66, 3842 ( 2000). 3. F. H.Chape lle et al., Nature 415, 312 (2 002). 4. Aqueo us Micro bial Geoch emis try in Extre me and Contaminated Environments, Fall AGU Meet ing, San Fr anc isco, CA, 6 to 10 Decembe r 20 02. See www.agu.or g/meetings/fm02/p rogram.shtml. 5. G . M o ri n et al., Fall AGU Me eting, San Fr ancisco, CA, 6 to 10 December 2002, abstract B22E-05. 6. C. M. H an se l et al., Fall AGU Meeting, San Francisco, CA, 6 to 10 Decembe r 2002, abstract B22E-10. 7. E. A. Haack, L. A. War re n, Fall AGU Meetin g, S an Francisco,CA, 6 to 10 December 2002,abstract B22E-06. 8. P. A.O’Da y, Rev.Geophys. 37, 249 (1 999). 9. N. R.Pa ce , Science 276, 734 (1 997). 10. B.J. Finl ay , Science 296, 1061 (2 002). 11. K. H. Nealson, D. A. Stahl, in Geomicrobiology: Interactions Between Microbes and Minerals ,J. F. Banf ield , K. H. Nealson, Eds. (Min era logi cal Socie ty of Ame ric a,Was hin gto n, DC, 199 7),vol. 35, pp . 5–3 4. 12. D. K. Newman, J. F. Banfield, Science 296, 1071 (2002). 13. A.S. Beliaev et al., J. Bacteriol. 184, 4612 ( 2002). 14. A.-L.Reysenbach,E. Shock, Science 296, 1077 (20 02). 15. K . J . Ed wa r ds , P. L. Bo nd , T. M. Gihr in g, J. F. Ba nf i el d, Science 287, 1796 (2 000). D ecades ago, excavations in the Tehuacan Valley of Mexico ( 1) con- vinced many archaeologists that they now had physical proof of how, when, and where plants were first domesti- cated in the New World. The proof came in the form of preserved seeds and fruits, maize kernels and cobs, fibers, and the rinds of cultigens found in cave soils and in preserved human feces originally dated as early as 7500 to 9000 years old. Little did these archaeolo- gists realize that the puzzle of New World plant domestication was far from solved. Decades later, they would learn that the most critical clues come not from the large and visual remains of plants, but from tiny microscopic particles that most archaeolo- gists unknowingly discarded. Fortunately, a few researchers (2, 3) were not convinced by the traditional sto- ry of New World cultigen origins. Piperno and a few others devoted more than three decades to searching the archaeological soils of Central and South America for microscopic phytoliths (plant crystals), tiny starch grains from domesticated plants, and fossil pollen (see the fig ure). As noted by Piperno and Stothert on pag e 105 4 of this iss ue ( 4) and by Piperno and Pearsall in a recent book ( 5), these microscopic traces of plants reli- ably record the earliest use of domesti- cated plants. Early speculation about the origins of New World plant domestica tion focused on the upland regions of Mexico and South America. These regions were fa- vored because they were easy to reach, of- ten contained caves or rock shelters f illed with preserved plant remains, and had yielded previous successes that ensured ARCHAEOLOGY Invisible Clues to New World Plant Domestication V aughn M. Bryant The author is in the Center for Ecological Arch- aeolo gy, Depart ment of An thropo logy , Te xas A&M Uni ver sit y, Co lleg e Stati on, TX 77843, USA. E-mail: [email protected] Enhanced online at www.sciencemag.org/cgi/ content/full/299/5609/1029 C R E D I T : P A N E L S A A N D B , D . P I P E R N O ; P A N E L C , J . J O N E S A B C Archaeology under the microscope. (A) Radiocarbon-dated 10,000-year-old phytolith (diameter 100 µm) of domesticated Cucurbita, collected from soil at the V egas Site 80 in Ecuado r. ( B) Reserve starch grain s from the root of a modern manioc plant. ( C) Maize pollen grain (diameter 75 µm) from cultural leve ls of the Kob Site, Belize, radiocarbon dat ed to ~5000 years ago. P E R S P E C T I V E S www.sciencemag.org SCIENCE VOL 299 14 FEBRUAR Y 20 03 1029 o n J a n u a r y 1 3 , 2 0 1 5 w w w . s c i e n c e m a g . o r g D o w n l o a d e d f r o m o n J a n u a r y 1 3 , 2 0 1 5 w w w . s c i e n c e m a g . o r g D o w n l o a d e d f r o m