The bird brain, though muchmaligned, can perform featswhile sleeping of which we

can only dream—namely, it can stayawake. Although it’s long been knownthat birds can sleep with one eye open,researchers at Indiana State Universityhave determined that ducks can care-fully choreograph sleeping and wakingstates simultaneously in different re-gions of the brain.

Earlier studies had shown that birdsachieve these two states of conscious-ness at once by splitting the tasks be-tween the brain: one hemisphere fallsasleep while the other stays awake andresponsive. This half-brain, or unihemi-spheric, sleeping manifests itself assomething like a prolonged wink; theeye connected to the wakeful half of thebrain remains open, whereas that wiredto the dozing half droops.

The coexistence of two states of con-sciousness is impressive enough, “butthe kicker,” Indiana State researcherNiels Rattenborg says, “is the control.”Because the hemispheres of birds’

brains process some information inde-pendently while awake, “it was con-ceivable that unihemispheric sleepingsimply occurred when the hemispheresfell asleep or awakened out of phase bychance,” explains Charles Amlaner, thesleep specialist of the team.

To rule out this possibility, the inves-tigators set about finding a situation inwhich ducks would want control overtheir sleep. They knew that some aquat-ic mammals—the only other group be-sides birds that displays unihemisphericsleep—keep half of the brain awake toensure that they keep one flipper pad-dling and so don’t drown while sleep-ing at sea. Sleeping in the water is ex-tremely specialized, however, and be-cause almost all birds demonstrateunihemispheric sleeping, the impetusbehind the evolution of this behaviorhad to be a more common threat—namely, predation. Much of animal be-havior “is influenced by the great riskof being killed,” notes team memberSteven Lima.

The researchers simulated a riskysleep situation by lining up four ducksin a row. Whereas the two ducks in thecentral positions could presumably feelbuffered by their neighbors fromthreats, those situated on either endwere more likely to feel vulnerable toattack on their exposed sides. “Animalsin general perceive more risk at the edgeof a group,” Rattenborg explains—a

News and Analysis26 Scientific American May 1999

world and represents what is termed amature epidemic. According to some es-timates, up to one third of the women inthe main trading centers are HIV-posi-tive, and the infection rate for the gener-al community is 16 percent. In contrast,Mwanza had a community HIV preva-lence of only 4 percent and in 1992 wasstill experiencing a relatively early HIVepidemic. The presence of STDs mayhave a far greater impact on HIV trans-mission during the early stages of anepidemic, rather than one where thevirus is already well established.

An additional factor may be Rakai’sbaseline rates of resistant and untreat-able STDs. Of reported genital ulcers, alarge percentage tested positive for her-pes, which is incurable. Bacterial vagi-nosis, a difficult-to-treat condition thathas been linked to increased risk forHIV infection, existed in 50 percent ofthe population at the beginning of thestudy. Though observed in East Africa, itwas not reported in the Mwanza study.

A third factor may be the treatmentapproach at Rakai. Periodic mass inter-vention did not specifically target symp-tomatic STDs, as was the case in Mwan-za. Wawer hypothesizes that at the popu-lation level, symptomatic STDs may havea greater effect on HIV transmission.Data from Rakai, however, suggest that asizable portion of symptomatic cases wasnot associated with a treatable STD.

“The whole issue of STD control forHIV prevention is, unfortunately, a lotmore complex than we hoped,” Wawersays, adding that there is a great need todo more research into different popula-tions with different STD and HIV back-grounds. There is one more communi-ty-based, randomized study currently inplace in Africa, and investigators hopeto present their results sometime nextyear. —Roxanne Nelson

ROXANNE NELSON, based inSeattle, described bloodless insulin mon-itors in the October 1998 issue.

Y2HotGlobal warming has topped itself again:1998 has set the record for the past mil-lennium. As reported in the March 15Geophysical Research Letters, MalcolmHughes of the University of Arizona andhis colleagues analyzed tree rings andice cores to reconstruct temperaturetrends over the past 10 centuries. Mostalarming is the past century’s abrupt re-versal of a 1,000-year-long coolingtrend, culminating in the 1990s beingthe warmest decade yet. One result ofthe warmth: early spring activity. Univer-sity of Munich researchers note in theFebruary 25 Nature that spring bloomsnow take place six days earlier than inthe 1960s and that the growing seasonlasts nearly 11 days longer. —J.N.

An Arm and a LegThe cost of an arm and a leg may behigh, but the two limbs are eerily inter-changeable, as reported in the March 12Science. Harvard University researchersmade leg structures grow where a wingshould have been. Three genes are in-volved in limb development, Pitx1, Tbx4

and Tbx5. Movingactive Pitx1 from theleg bud to the wingbud, where thegene is normally in-active, began legformation there.Wings did not com-plete their new pathtoward legginess,but they did be-come distinctly leg-

like: feathers were lost, muscle structurechanged, and digits and claws appeared(photograph). —J.N.

Temper, TemperDavid J. Green of Pennsylvania State Uni-versity and his colleagues have devised away for tempered glass to crack withoutshattering. Tempering strengthens glassby compressing the molecules of theouter surface; if that surface cracks, thepent-up stress is released, exploding therest of the glass. The researchers de-scribe in Science a chemical method tomake deeper layers in the glass denserby substituting sodium atoms with larg-er potassium atoms. Cracks could appearon the less dense outer layer but fail toreach any deeper. The method couldlead to thinner glasses for scanners, pho-tocopy machines and displays. —P.Y.

In Brief, continued from page 24

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BEHAVIOR

Copyright 1999 Scientific American, Inc.

The long search for extraterres-trial intelligence has foundnone, but it has revealed some-

thing interesting about a certain formof terrestrial intelligence: namely, thatwhen scientists get on to an idea theybelieve is truly important, somethingthat could shake civilization to its cen-ter, failure no longer discourages—it mo-tivates. Some 30 years of listening todeep-space radio waves is culminating

with the conclusion next year of ProjectPhoenix, the best-funded, most ambi-tious search yet for signals from the1,000 neighboring star systems mostlikely to harbor life. There is not a sin-gle repeatable observation of an artifi-cial radio signal to show for all that ef-fort. Yet the SETI community is ener-gized, buzzing with new plans, includingone to build a giant telescope array de-voted to the search.

This is not the first time that the faith-ful have bounced back from adversity.Indeed, Project Phoenix rose from theashes of a National Aeronautics andSpace Administration program that wasterminated by Congress after less thantwo years. Phoenix was funded by theSETI Institute in Mountain View, Calif.,and backed by several computer indus-

try tycoons, yet it had to beg time onmajor radio observatories. “We get 10days a year at Arecibo in Puerto Rico;that’s not much,” complains William“Jack” Welch, who holds an endowedchair for SETI that the University ofCalifornia at Berkeley created in June,suggesting a growing acceptance of thefield among mainstream astronomers.

That and perhaps the rapidly accumu-lating resources of its billionaire donorshave emboldened the SETI Institute todesign a 10,000-square-meter radio an-tenna—the One Hectare Telescope, or1HT—whose primary mission would beto search for aliens. “The idea is to buildan instrument that would have as muchcollecting area as the new [government-owned] 100-meter dish at Green Bank,W.Va., but cost only a third of its $75-million price,” Welch explains.

To save money, the 1HT would beconstructed from mass-produced satel-lite TV dishes, 500 to 1,000 of themspread across the countryside in north-ern California. To amplify the signalsreceived in a huge spectrum from 300megahertz to perhaps 10 gigahertz, ev-ery antenna would have a custom-de-signed microchip, no bigger than a sug-ar cube and costing only a few hundreddollars, Welch says. Filtering that riotof signals to pick out a single, all-im-portant anomalous spike will take seri-ous computing power. Welch concedesthat the processing is “an order of mag-nitude more challenging than what’sbeen done before.”

Although the 1HT would be used pri-marily for SETI surveys, Welch pointsout that it could also serve as a criticalstepping stone for radio astronomerswho hope to construct a mammoth in-strument with 100 times the collectingarea of the 1HT, at a cost of perhaps$600 million. The Chinese are advocat-ing up to 30 Arecibo-like dishes erectedin karst depressions in China. Australiansprefer arrays of flat panels in the out-back. But Welch argues that a few thou-sand consumer satellite dishes might per-form just as well at half the price.

Even as the traditionalist alien huntersplan to sift once more through the ra-dio spectrum with ever finer combs,several high-profile astronomers are be-ginning to look for optical beacons. Inone analysis, Harvard University physi-cist Paul Horowitz estimated that the$1-billion Helios laser being planned atLawrence Livermore National Labora-tory could send nanosecond-long pulsesthat would appear 3,000 times brighter

News and Analysis28 Scientific American May 1999

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EXTRATERRESTRIAL INTELLIGENCE

phenomenon known as the edge effect.The ducks on the edge spent 2.5

times longer in unihemispheric sleepthan ducks in the central spots did.They also directed their open eye to-ward the unprotected flank during 86percent of their unihemispheric sleepingtime, whereas the central ducks indicat-ed no preference for which eye theykept open. Some edge ducks even didthis the entire time, periodically turningaround to switch eyes. Half-sleepingducks shown a video image simulatingan approaching predator roused in-stantly, indicating that the open eye wasalert. Far from being an accidental con-sequence of their sleepy state, theducks’ half-sleeping behavior demon-strated that they can direct the alerthemisphere and eye to stand guard.

But if unihemispheric sleeping is sovaluable for detecting predators’ at-tacks, why don’t more animals do it?The answer seems to be that they losttheir chance a long time ago. ChristianMathews, working in Amlaner’s lab,

recently found that lizards also sleepwith one eye open, especially after theyhave seen a predator. This behaviormay not technically qualify as unihemi-spheric sleep, because lizards’ sleepingbrain waves differ in general from thoseof birds and mammals. But the fact thatlizards have a similar behavior out-wardly indicates that this sleeping statemay have been shared by an early com-mon ancestor.

Early mammals probably spent muchof their day sleeping safely in their bur-rows, Amlaner reasons. As birds refinedvigilant sleeping, early mammals mayhave lost much of the ability, only rede-veloping unihemispheric sleep under themost extreme evolutionary circum-stances, such as becoming aquatic. In-terestingly, Rattenborg notes, humanswho have undergone a severe traumadisplay sleeping brain-wave patternsreminiscent of those of birds in unihemi-spheric sleep. Perhaps some very oldpart of their brain is telling them to keepan eye open for danger. —Jessa Netting

DUCKS AT THE ENDSsleep with one eye open(inset; eyelid is white)

more so than the twomiddle ducks, whichpresumably feel safer.

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