Many bees, ants and wasps live together in highly cooperative societies primarily because this lifestyle offers a good way of passing down the family genes, not because it makes their own lives easier, new research suggests.

Scientists compared the mating behavior of females in 267 species of bees, wasps, and ants. They found that in the older species, females were always monogamous.

This finding supports the idea that monogamy - and, by extension, a high level of relatedness -- was key to the evolution of eusociality (many animals live together as a group without necessarily being social).

"It's marvelous to be able to do assembly and control at this fine a resolution with such very, very tiny things," said Bruce Donald, a Duke professor of computer science and biochemistry.

Each microrobot is shaped something like a spatula but with dimensions measuring just microns, or millionths of a meter. They are almost 100 times smaller than any previous robotic designs of their kind and weigh even less, Donald added.

Formally known as microelectromechanical system (MEMS) microrobots, the devices are of suitable scale for Lilliputian tasks such as moving around the interiors of laboratories-on-a-chip.

In videos produced by the team, two microrobots can be seen pirouetting to the music of a Strauss waltz on a dance floor just 1 millimeter across. In another sequence, the devices pivot in a precise fashion whenever their boom-like steering arms are drawn down to the surface by an electric charge. This response resembles the way dirt bikers turn by extending a boot heel.

New research summaries describe the group's latest accomplishment: getting five of the devices to group-maneuver in cooperation under the same control system.

"Our work constitutes the first implementation of an untethered, multi-microrobotic system," Donald's team writes in a report to be presented on June 1-2, 2008 during the Hilton Head Workshop on Solid State Sensors, Actuators and Microsystems in South Carolina.

More comprehensive details on how the scientists achieve this "microassembly" will be published later in their report for the Journal of Microelectromechanical Systems.

The research was funded by the National Institutes of Health and the Department of Homeland Security, and also included Donald's graduate student Igor Paprotny and Dartmouth College physicist Christopher Levey.

Donald has been working on various versions of the MEMS microrobots since 1992, initially at Cornell and then at Stanford and Dartmouth before coming to Duke. The first versions were arrays of microorganism-mimicking ciliary arms that could "move objects such as microchips on top of them in the same way that a singer in a rock band will crowd surf," he said. "We made 15,000 silicon cilia in a square inch."

A February 2006 report in the Journal of Microelectromechanical Systems by Donald, Paprotny, Levey and others detailed the basics of the current design: devices about 60 microns wide, 250 microns long and 10 microns high that each run off power scavenged from an electrified surface.

Propelling themselves across such surfaces in an inchworm-like fashion impelled by a "scratch-drive" motion actuator, the microrobots advance in steps only 10 to 20 billionths of a meter each, but repeated as often as 20,000 times a second.

The microrobots can be so small because they are not encumbered by leash-like tethers attached to an external control system. Built with microchip fabrication techniques, they are each designed to respond differently to the same single "global control signal" as voltages charge and discharge on their working parts.

This global control is akin to ways proteins in cells respond to chemical signals, said Donald, who also uses computer algorithms to study processes in biochemistry and biology.

In their new reports, the team shows that five of the microrobots can be made to advance, turn and circle together in pre-planned ways when each is built with slightly different dimensions and stiffness.

Following a choreography mapped out with the aid of mathematics, the microdevices ultimately assemble into group micro-huddles that could set the stage for something more elaborate.

"Initially, we wanted to build something like a car that could drive around at the microscopic scale," Donald said. "Now what we've been able to do is create the first microscopic traffic jam."

He said it took him and various colleagues from 1997 to 2002 to create a microrobot that can operate without a tether, three more years to make the devices steer under global control, and another three to independently maneuver more than one at a time.

"The hard thing was designing how multiple microrobots can all work independently, even while they receive the same power and control," he said.

The study's author, Vanessa Gail Perry, Assistant Professor at the George Washington University School of Business, concludes that "Overestimating credit ratings is partly a function of a lack of financial sophistication. In addition, it appears that people who have overestimated their credit rating take less care in managing their finances.”

Professor Perry analyzed data from the Freddie Mac Consumer Credit Survey. The survey collected data on attitudes, behaviors, knowledge and experiences with credit and financial management from around 23,000 people. Results indicate that approximately 32 percent of respondents overestimated their credit ratings, while only four percent underestimated their credit ratings. The findings support previous studies in judgment and decision-making that show that individuals are more likely to be overconfident about their knowledge or abilities.

Those who overestimated their credit ratings had lower incomes, less formal education, and were less likely to own their homes. They were also more likely to be African-American, Hispanic, or female. One possible explanation for these results is that minority consumers in general have less experience with financial markets which in turn affects their tendency to overestimate their credit rating.

Psychologists now believe there is some truth to this argument. Rather than picking our friends based on intentional choice and common values and interests, our friendships may be based on more superficial factors like proximity (think neighbors) or group assignments (your department at work).

Mitja Back, Stefan Schmukle, and Boris Egloff of the University of Leipzig sought to test the notion that random proximity and random group assignment at zero acquaintance would foster friendship in the long run. The researchers investigated 54 college freshmen upon encountering one another for the first time at the beginning of a one-off introductory session and randomly assigned them a seat number in a group of chairs organized in rows.

As reported in a recent issue of Psychological Science, a journal of the Association for Psychological Science, sitting in neighboring seats as a result of randomly assigned seat numbers when meeting for the first time led to higher ratings of friendship intensity one year later. The same was true even if participants were merely in the same row.

The counterintuitive finding suggests that friendships may not be as deliberate we think. “In a nutshell,” write the authors, “people may become friends simply because they drew the right random number.”