What happens to a stem cell at the molecular level that causes it to become one type of cell rather than another? In studies that mark a major step forward in our understanding of stem cells' fates, a team of Caltech researchers has traced the stepwise developmental process that ensures certain stem cells will become T cells—cells of the immune system that help destroy invading pathogens. 

The second-largest mass extinction in Earth's history coincided with a short but intense ice age. Although it has long been agreed that the so-called Late Ordovician mass extinction was related to climate change, exactly how the change produced the extinction has not been known. Now, a team led by Caltech scientists has determined that the majority of extinctions were caused by habitat loss due to falling sea levels and cooling of the tropical oceans.

Scientists have further narrowed the search for a hypothetical particle that could be dark matter, the mysterious stuff that makes up 80 percent of all the mass in the universe. Caltech postdoc Jennifer Siegal-Gaskins presented the researchers' results, compiled from two years' worth of data from NASA's Fermi Gamma-ray Space Telescope, at a meeting of the American Physical Society in Atlanta earlier this week.

When jurors consider shortening the prison sentences of convicted criminals, they use parts of the brain associated with sympathy and making moral judgments, according to new work by Caltech neuroeconomist Colin Camerer and colleagues. They found that the most lenient jurors show heightened levels of activity in a brain region associated with discomfort, pain, and imagining the pain that others feel.

In the continual quest for better thermoelectric materials—which convert heat into electricity and vice versa—researchers have identified a liquid-like compound whose properties give it the potential to be even more efficient than traditional thermoelectrics.

Astronomers have found celestial objects called quasars that bend and distort the light coming from galaxies behind them. The discovery may finally allow astronomers to determine the masses of galaxies that host quasars.

An international team of physicists—including several from the California Institute of Technology (Caltech)—has detected and measured, for the first time, a transformation of one particular type of neutrino into another type. The finding, physicists say, may help solve some of the biggest mysteries about the universe, such as why the universe contains more matter than antimatter—a phenomenon that explains why stars, planets, and people exist at all.

In both animals and humans, vocal signals used for communication contain a wide array of different sounds that are determined by the vibrational frequencies of vocal cords. Knowing how the brain sorts out these different frequencies—which are called frequency-modulated (FM) sweeps—is believed to be essential to understanding many hearing-related behaviors, like speech. Now, a pair of biologists at Caltech has identified how and where the brain processes this type of sound signal.

Many of us see a man in the moon—a human face smiling down at us from the lunar surface. The "face," of course, is just an illusion, shaped by the dark splotches of lunar maria (smooth plains formed from the lava of ancient volcanic eruptions). Like a loyal friend, the man is always there, constantly gazing at us as the moon revolves around Earth. But why did the moon settle into an orbit with the man facing Earth?

Nearly all motile bacteria can sense and respond to their surroundings through a process called chemotaxis, which begins with proteins known as chemoreceptors. Now researchers at Caltech have built the first model that depicts precisely how chemoreceptors and the proteins around them are structured at the sensing tip of bacteria. Because chemotaxis plays a critical role in the first steps of bacterial infection, a better understanding of the process could pave the way for the development of new, more effective antibiotics.