Everyone who has an e-mail account has probably received a forwarded chain letter promising good luck if the message is forwarded on to others--or terrible misfortune if it isn't. The sheer volume of forwarded messages such as chain letters, online petitions, jokes and other materials leads to a simple question--how do these messages reach so many people so quickly?

One of the most famous figures in psychology is the following:

Changing the sugars attached to a hormone produced in the pituitary gland increased fertility levels in mice nearly 50 percent, a research group at Washington University School of Medicine in St. Louis has found. The change appears to alter a reproductive "thermostat," unveiling part of an intricate regulatory system that may one day be used to enhance human fertility.

New observations from NASA's Mars Reconnaissance Orbiter indicate that the crust and upper mantle of Mars are stiffer and colder than previously thought. The findings suggest any liquid water that might exist below the planet's surface and any possible organisms living in that water, would be located deeper than scientists had suspected.

Studies of how cancer cells spread have led to a surprising discovery about the creation of cells with adult stem-cell characteristics, offering potentially major implications for regenerative medicine and for cancer treatment.

A world-renowned team of experts in biomechanics and physiology from six universities, led by Professor Hugh Herr of the Massachusetts Institute of Technology’s Media Lab, refute scientific claims that the prostheses worn by Oscar Pistorius, a 21-year-old South African bilateral amputee track athlete, provide him with an unfair advantage in the 400-meter race.

Researchers from the University of Pennsylvania School of Medicine have shown, in unprecedented detail, how a small molecule is able to selectively take apart abnormally folded protein fibers connected to Alzheimer's disease and prion diseases. The findings appear online this week in the Proceedings of the National Academy of Sciences. Finding a way to dismantle misfolded proteins has implications for new treatments for a host of neurodegenerative diseases.

A new study reveals the genetic identity of human immunodeficiency virus (HIV), the version responsible for sexual transmission, in unprecedented detail. Scientists found that among billions of HIV variants only a few lead to sexual transmission.

Cancer, nervous system disorders such as Parkinson’s disease, cardiovascular disorders and old age have one thing in common: Both in afflicted tissue and in aging cells, scientists have observed oxidative changes in important biomolecules. These are caused by reactive oxygen molecules, including the notorious “free radicals” that are formed as a by-product of cellular respiration and attack cellular proteins, nucleic and fatty acids.

An obese oddball of a star has left astronomers wondering how it could have formed. Found with the Arecibo radio telescope in Puerto Rico, the star is a pulsar – a compact, rapidly spinning star – called J1903+0327. It lies 20,000 light-years away spinning at a rate of 465 revolutions per second – the fifth fastest-spinning pulsar known in our Galaxy.