Left Behind
Ned Flanders’s Leftorium would not have stood a chance in Victorian England. Left-handers made up only about 3 percent of the population there, as compared with about 11 percent today globally [see “Taking Sides”; SciAm, April 2006, and “Left Out”; SciAm Mind, December 2005]. Researchers came to this conclusion after watching documentary films about northern England from 1897 to 1913, some of which showed people waving (a better indicator of handedness than writing). The dearth did not result from increased mortality—most of the southpaw wavers were older folks. The investigators speculate that social stigmatization may have led to their decline in the 19th century, as the industrial revolution produced machines suited for right-handers rather than left-handers. That disparity made lefties stand out, and they were presumably shunned as marriage partners. The study appears in the September 18 Current Biology.
Insulin-Resistant Memory
Alzheimer’s disease may be a novel variety of diabetes. Researchers at Northwestern University experimented with a form of amyloid beta–derived diffusible ligands (ADDLs), which are small, soluble proteins that can travel around the body like hormones. Like amyloid beta and tau proteins, these molecules are often found in the brains of Alzheimer’s patients.
Applying ADDLs to mature cultures of hippocampal neurons, the researchers found that the proteins specifically bind to the tips of nerve endings at synapses. This precise attachment quickly shut down the replenishment of insulin receptors by inhibiting their transport from the cell body, where they are manufactured. The resulting resistance to insulin, a hormone that helps cells regulate the metabolism of sugar, destroys the capability of memory neurons to communicate properly.
Based on such evidence, investigators have begun to view Alzheimer’s disease less as nerve cell death and more like synapse failure. According to team leader William Klein, who published the work August 24 online in the FASEB Journal, this perspective could clarify why some people have an abundant number of plaques yet remain cognitively healthy and why elderly type 2 diabetics usually have memory problems.
—Peter Sergo
Meat-Loving Hatchlings
The time after hatchling sea turtles scamper down a beach and before they return years later as egg-laying adults has largely been a natural history mystery [see, for instance, “How Sea Turtles Navigate”; SciAm, January 1992]. Biologists at the University of Florida report key insights into these “lost years” online September 18 in Biology Letters. The team examined nitrogen isotopes in shell samples; this so-called stable isotope analysis reveals where an animal resides in the food chain—a skew toward heavy isotopes from light isotopes suggests a meatier diet. From their analyses, the researchers conclude that green sea turtles are initially carnivorous, preying on jellyfish and other creatures; three to five years later the turtles switch to sea grass and move closer to shore.
Killing the Kilogram
In September news reports proclaimed that the kilogram was mysteriously losing mass. Specifically, the reference cylinder, made 118 years ago and kept locked away under glass in France, appears to have lost 50 micrograms when compared with the average of dozens of copies. Physicists have long recognized this kind of mass drift, however, which is why they have been seeking natural definitions for the kilogram. One possibility for a new definition would be the number of silicon atoms in a kilogram of pure silicon; another would rely on electrical power and quantum effects.
