I N F O RM A T I O N T E C H N O L O G Y42 Stopping Spam BY JOSHUA GOODMAN, DAVID HECKERMAN AND ROBERT ROUNTHWAITETorrents of junk e-mail threaten to undermine Internet communications, but a combination of techniques might make the problem manageable again.E A R T H S C I E N C E50 Probing the Geodynamo BY GARY A . GL ATZMA IER A ND PETER OLSONStudies of our planet’s churning interior offer intriguing clues to why the earth’s magnetic field occasionally fl ps and when the next reversal may begin.B I O T E C H N O L O G Y58 The Alternative Genome BY GIL A STContrary to the old “one gene, one protein” axiom, complex organisms coax more flexibility from their DNA by having small numbers of genes do the work of many.D E C I S I O N M A K I N G66 Shaping the Future BY S TEVEN W. POPPER, ROBERT J . LEMPERT AND STEVEN C . BANKESGiven the unavoidable uncertainty of the long-term future, a new analytical approach to setting policy may help with problems such as global warming.B E H A V I O R A L E C O N O M I C S72 How Animals Do Business BY FRANS B. M. DE WA ALHumans and other animals share a heritage of economic tendencies, including cooperation, repayment of favors and resentment of unfair pay.M A T E R I A L S S C I E N C E80 Low-Temperature Superconductivity Is Warming Up BY PAUL C . C ANFIELD AND SERGE Y L . BUD’KOMagnesium diboride is not merely an unexpectedly good superconductor. Properly prepared, it outperforms the materials that are currently industrial favorites.I N N O V A T I O N88 A Toxin against Pain BY GARY S TIXA recently approved analgesic that is a synthetic version of a toxin from a sea snail offers hope for relief from intractable pain.