Scientists solve mystery of patients with Alzheimer's plaques but no disease
The only way physicians can confirm that someone suffered from Alzheimer's disease is if an autopsy reveals a protein called amyloid beta (Aß) accumulated in a postmortem brain. But doctors occasionally find these plaques in the brains of deceased people who showed no Alzheimer's symptoms. Now Harvard Medical School researchers say they know why: Aß comes in several varieties, but apparently only one of them causes the memory-ravaging effects of Alzheimer's. The team writes in the journal Nature Medicine that they injected four varieties of the protein into the brains of rats to determine which versions cause Alzheimer's-like symptoms. Much to their surprise, only one did: a two-molecule form of the protein that is dissolvable in water. This type of Aß not only curtailed memory, but also destroyed about half of the cells in the rats' brains. By identifying the disease-causing variant of the protein, researchers can now refocus their efforts on a more specific target to fight Alzheimer's.

Out on a limb: fish-to-land-animal fossil link unearthed
Scientists have unearthed more fossil remains of a four-legged crocodilelike creature that help explain the evolution of fish to advanced landlubbers.Among the 365-million-year-old cache of fossils found in Latvia: a skull, jawbone, shoulder and a piece of pelvis. Working with these telltale fragments, researchers led by Per Ahlberg, an evolutionary biologist at Uppsala University in Sweden, reconstructed what the body of this ancient creature, dubbed Ventastega, probably looked like. Though decidedly crocodilian in appearance, this primitive land-walker likely sported a big back fin instead of a tail. Ventastega belongs to the tetrapod group, which evolutionarily transitioned into animals, including ourselves, with four limbs. But scientists report in Nature that they do not know if Ventastega itself spawned descendant species or died out as an evolutionary dead-end. Either way, at least it was on the right track.

U.S. intel: Worsening global warming may ignite political instability
Without curbs on greenhouse gas emissions, the volume of warming pollution worldwide could hit 42.3 billion metric tons per year by 2030—a 51 percent increase over present levels, according to a report released this week by the U.S. Department of Energy's Energy Information Administration. This gloomy, worst-case scenario also foresees oil prices of $186 per barrel and a world that consumes 50 percent more energy, mostly fossil fuels. Such a lack of action could also lead to global instability, according to a classified National Intelligence Assessment report (pdf) presented to Congress this week by the U.S.'s 16 intelligence agencies. The report concludes that climate change over the next two decades will contribute to political instability in Africa and Asia, due to changing rainfall patterns or an increase in extreme weather. The U.S. would remain relatively unaffected—other than some thawing in Alaska, water shortages in the Southwest and storm surges on the eastern and southern coasts. The U.S., however, may benefit from increased crop yields, although its military may be stretched dealing with global "humanitarian emergencies" (spawned by devastating natural disasters and regional conflicts).

Lemurs may use a smelly sleight of hand to identify, trick one another
New research indicates that the wide-eyed primates called ring-tailed lemurs give off different scents from each of their tiny hands. Leonardo Dapporto, a biologist at the University of Florence in Italy, discovered this odd trait during a study that involved squeezing the scent glands in the hands of seven male lemurs at Italian zoos in Tuscany and Friuli. Because it is known that lemurs maintain personalized scents throughout their lives, Dapporto expected little variation between the hands' secretions. But a chemical analysis revealed that the scents of the left and right hands of each subject varied enough to appear to be from two different animals. In a paper published in the journal Naturwissenschaften,* Dapporto suggests that having two smelly signatures may aid lemurs in identifying one another (sort of like recognizing a human by unique shades and a distinctive hat) or in deceiving enemies about the size of a particular community: Lemurs live in competitive groups and use scent to mark their territory; potential invaders may think twice if they believe rival packs are too big to conquer.

Is this sinking in? Teaching computers to teach better
Classroom teachers can usually tell if they're getting their point across by the look on their students' faces—blank stares are a dead giveaway that the information is not sinking in. And online "instructors" may soon have the same tool available to gauge comprehension. So-called "intelligent tutoring systems" that use computers and artificial intelligence to administer lessons, assess performance and provide feedback have been growing in popularity since first introduced in the 1970s. Researchers at the University of California, San Diego's Jacobs School of Engineering are developing software that will allow students to control  how quickly or slowly these automated lessons are presented—even rewinding when necessary—through facial expressions that signal their comprehension or confusion. To collect samples of expressions linked to learning, lead researcher Jacob Whitehill, a U.C. San Diego computer science PhD student, taught eight people in his lab about German grammar and recorded the sessions using video conferencing software. He found that the students blinked less frequently during difficult parts than when easier portions of the lecture were presented. He and his colleagues continue to observe other associated facial expressions that they can incorporate into software, which will enable computers to "read" students faces to tailor learning packages to individual users.

Call of the wild: Baby crocodiles cry, "Let us out!"
Like the cheep-cheep of chicks, a new study finds that baby crocs cry while still inside their eggs to let one another, and mom, know it's time to hatch. Researchers from Université Jean Monnet in Saint-Etienne, France, took eggs and their mothers and played them either recordings of calls made by unhatched baby crocs (which sounded like "umph, umph") or nonspecific noise. They report in Current Biology that soon-to-be hatchlings treated to the recorded calls responded more frequently and were egged on to hatch either during the recording or within 10 minutes of it. Only one croc came out of its shell during the recorded general noise; the rest hatched hours later. Eight of 10 mothers exposed to alternating calls and noise began digging up their nests on hearing the recorded cries. Researchers say the call and response may be a means of synchronizing hatch time so that all the hatchlings get adult care and protection from predators.

Scientists: World still safe from mini black holes
Need proof the Large Hadron Collider (LHC) won't destroy the world after it is switched on in a few months and starts smashing protons together at energies never before attained by human beings? Just look up. In an attempt to nix lingering public concern that the $8-billion particle accelerator might produce microscopic, world-eating black holes, the European Organization for Nuclear Research (CERN), which built it, asked five physicists to weigh in on the subject one more time. In a report published this week, they dismiss worries, noting that the LHC particle collisions are essentially re-creations of cosmic rays (high-energy particles from space), which bombard stars and planets throughout the universe and attain much higher energies than the new machine will generate. They conclude that if such bombardments were capable of making apocalyptic black holes, then stars would have already accumulated them and been consumed. We see stars, they say—ergo, micro–black holes are no threat. But what do scientists know?

Florida sugar purchase sweetens chances of Everglades restoration
Florida taxpayers may soon shell out $1.75 billion (via a water bill surcharge) to buy the company U.S. Sugar and its 187,000 acres (75,675 hectares) of sugarcane just north of Everglades National Park. In recent decades, the sugar manufacturer has been contaminating water in the giant wetland with polluted runoff from its fields. The deal would end that within the next six years, because the state plans to shut it down and restore the natural water flow. State lawmakers must approve the sale.

Slimy surfers: snails ride their own gooey wave
Ever see a snail crawling on the surface of water? How about on its underside? Scientists believe they may have figured out how these crafty mollusks pull off this tricky feat. When right side up, snails poke along using adhesive locomotion. This method of movement works through the release of mucus that acts as an adhesive or as a flowing liquid, depending on the pressure applied by contracting muscles in the gastropod's "foot" (the part of the snail that touches a surface). But how do upside-down snails manage to do this on water? Sungyon Lee, an engineer at the Massachusetts Institute of Technology, indicates in an unpublished study that the undulations of the snail's foot disrupt the smooth "edge" of the water. This generates pressure that makes the mucus between the foot and the rippling water flow, carrying the snail along for the ride. In other words, it appears that the snail makes its own tiny waves to surf on with a board made of slime. Lee acknowledges that more research is needed to confirm the mechanics of this mode of motion. In the meantime, enjoy the thrills and spills of the common freshwater snail: The paper notes that though these super-slow escargot shred through the water at less than 24 feet (7.3 meters) per hour, they can pull gnarly 180-degree turns in just three seconds.

Gun-related murders on the rise among young urban men
A new study shows that gun-related homicides among young men in the U.S. spiked dramatically between 1999 and 2005. The report, published in the online edition of the Journal of Urban Health came on the heels of a Supreme Court decision that a ban on handguns in Washington, D.C., is unconstitutional. According to the study by Johns Hopkins Bloomberg School of Public health, murders involving firearms increased by 31 percent among black men ages 25 to 44 and by 12 percent among white men of the same age during the same years the study covers. The researchers analyzed data from the U.S. Department of Health and Human Services's Web-based Injury Statistics Query and Reporting System, which includes information on injury-related deaths and mortality rates per 100,000 population from 1981 to 2005. Researchers found that the overall homicide rate remained between 6.0 and 6.1 deaths per 100,000 (other than an increase in 2001 attributed to the terrorist attacks of September 11). The most significant increases in gun deaths occurred in Alabama, California, Michigan, Minnesota, Nebraska, Nevada, New Jersey, Ohio, Pennsylvania, Texas and Washington State—mostly in and around large metropolitan areas. Factors that may influence urban homicide trends, the study says, include early exposure to lead and unusually high rates of gun homicides surrounding the victims during their adolescence.

*Correction (6/30/08): Naturwissenschaften was originally identified as an Italian journal; it is German.