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Researchers have long known that women whose families include fraternal twins are more likely to give birth to twins themselves, and they're finally starting to figure out why. After scanning data from nearly 2000 mothers of fraternal twins, scientists from eight countries found two genes that increase a woman's chance of having twins-one that affects hormone levels and another that may alter how ovaries respond to them. The second of these may also have implications for why some women respond better than others to in vitro fertilization.

After the third time he nearly died but before the fourth, David Fajgenbaum embraced a new motto: Think it, do it. "I got out of the hospital with this profound sense of, you need to make the most of every second," he says. A former college football player with close-cropped dark hair and a firm handshake, Fajgenbaum, 31, is the picture of youthful vigor now. But that belies a frightening reality. Tomorrow the symptoms with which he's all too familiar could return, sending him to the intensive care unit (ICU) with every organ failing. 

In the largest study of its kind, a research team has meshed extensive genome data on more than 50,000 people with their electronic health records and identified potential new disease-causing genes. The data further suggest that about one in 250 people may harbor a gene variant that puts them at risk for heart attacks and strokes, yet aren't receiving adequate treatment.

A deadly disease known as African sleeping sickness has puzzled doctors for decades. It would disappear from villages without a trace, only to re-emerge weeks or months later with no known cause. Frustrated health officials wondered how sleeping sickness could persist when not a single villager or animal-the disease's only carriers-tested positive for the insect-borne parasite that causes it. Now, scientists may have an answer at last: They've discovered the disease was hiding in plain sight this whole time, living in and even transmitting via human skin.

It's one of the big mysteries of cell biology. Why do mitochondria-the oval-shaped structures that power our cells-have their own DNA, and why have they kept it when the cell itself has plenty of its own genetic material? A new study may have found an answer. Scientists think that mitochondria were once independent single-celled organisms until, more than a billion years ago, they were swallowed by larger cells. Instead of being digested, they settled down and developed a mutually beneficial relationship developed with their hosts that eventually enabled the rise of more complex life, like today's plants and animals.

At first, the researchers assumed that genes would shut down shortly after death, like the parts of a car that has run out of gas. What they found instead was that hundreds of genes ramped up. Although most of these genes upped their activity in the first 24 hours after the animals expired and then tapered off, in the fish some genes remained active 4 days after death.

Sometimes, a genetic tweak can make a really big difference in an animal's appearance. That's what likely happened when the predecessors of modern snakes lost their legs, a process that started some 150 million years ago, two separate groups of scientists have discovered. Although the teams took very different approaches to solve the mystery of how those limbs vanished, both came up with similar results: Mutations in DNA located near a gene key to limb formation keep that gene from ever turning on, they report today.

New research shows butterflies use nectar to drug unsuspecting ants with mind-altering chemicals. The Japanese oakblue butterfly (Narathura japonica) enlists the help of ants (Pristomyrmex punctatus) to stand guard and protect its growing caterpillars (pictured) from predators such as wasps and spiders.

An "excuse me" might be nice. Researchers have found that Earth belches a potent greenhouse gas known as tetrafluoromethane (CF4) during earthquakes and other tectonic events. The emissions likely aren't making a significant contribution to global warming, but the findings could change the way scientists model future climate scenarios. They also complicate the use of CF4 as a way to measure how the continents and climate have changed over millennia.

If the holy grail of medieval alchemists was turning lead into gold, how much more magical would it be to draw gold from, well, poop? It turns out that a ton of sludge, the goo left behind when treating sewage, could contain several hundred dollars' worth of metals-potentially enough to generate millions of dollars worth of gold, silver, and other minerals each year for a city of a million people.

Why did you get the flu this winter, but your co-workers didn't? The answer, according to a new study of twins, may have less to do with your genes and more to do with your environment-including your past exposure to pathogens and vaccines. Our immune system is incredibly complex, with diverse armies of white blood cells and signal-sending proteins coursing through our veins, ready to mount an attack on would-be invaders. Everyone's immune system is slightly different-a unique mixture of hundreds of these cells and proteins. But the main driver of this variation is unclear. Although scientists know that our immune system can adapt to our environment-that's why vaccines work, for instance-it is also built by our genes.

The most venomous animal on the planet isn't a snake, a spider, or a scorpion; it's a snail-a cone snail, to be precise. The Conus genus boasts a large variety of marine snails that have adopted an equally diverse assortment of venoms. Online today in the Proceedings of the National Academy of Sciences, researchers report an especially interesting addition to the animals' arsenal: insulin. According to the paper, this marks the first time insulin has been discovered as a component of venom.

Why elephants aren't riddled with tumors poses a weighty problem for researchers. A new study shows that the animals harbor dozens of extra copies of one of the most powerful cancer-preventing genes. These bonus genes might enable elephants to weed out potentially cancerous cells before they can grow into tumors.

Why does a snake have 25 or more rows of ribs, whereas a mouse has only 13? The answer, according to a new study, may lie in "junk DNA," large chunks of an animal's genome that were once thought to be useless. The findings could help explain how dramatic changes in body shape have occurred over evolutionary history. Scientists began discovering junk DNA sequences in the 1960s. These stretches of the genome-also known as noncoding DNA-contain the same genetic alphabet found in genes, but they don't code for the proteins that make us who we are. As a result, many researchers long believed this mysterious genetic material was simply DNA debris accumulated over the course of evolution. But over the past couple decades, geneticists have discovered that this so-called junk is anything but. It has important functions, such as switching genes on and off and setting the timing for changes in gene activity. 

She wanted to understand the effects of mutations that the gene for p53 is prone to. In dozens of simulations, she and her colleagues tracked how common p53 mutations further destabilize the already floppy protein, distorting it and preventing it from binding to DNA. Some simulations also revealed something else: a fingerhold for a potential drug. Once in a while, a small cleft forms in the mutated protein's core. When Amaro added virtual drug molecules into her models, the compounds lodged in that cleft, stabilizing p53 just enough to allow it to resume its normal functions.

Now, a new study reports that at least one species of songbird-and likely many more-already knows how to prep its chicks for a warming world. They do so by emitting special calls to the embryos inside their eggs, which can hear and learn external sounds. This is the first time scientists have found animals using sound to affect the growth, development, behavior, and reproductive success of their offspring, and adds to a growing body of research revealing that birds can "doctor" their eggs.

Collection of annotated research papers and accompanying teaching materials for top tier scientific journal "Science"

It concludes that the so-called stimulus-triggered acquisition of pluripotency (STAP) stem cells, as well as the chimeric mice and teratomas supposedly derived from those cells, "all originated in cultures contaminated with (embryonic stem) cells, a fact that refutes all of the main conclusions of the two papers" that reported the the supposed breakthrough method of reprogramming adult cells. Those two papers, an article and a letter, appeared online in Nature on 29 January.

We see color because of specialized light-sensing cells in our eyes called cones. One type, L-cones, sees the reds of strawberries and fire trucks; M-cones detect green leaves, and S-cones let us know the sky is blue. But vision scientists have now discovered that not all cones sense color (see video).

Adam Ruben's tongue-in-cheek column about the common difficulties and frustrations of reading a scientific paper broadly resonated among Science Careers readers. Many of you have come to us asking for more (and more serious) advice on how to make sense of the scientific literature, so we've asked a dozen scientists at different career stages and in a broad range of fields to tell us how they do it. Although it is clear that reading scientific papers becomes easier with experience, the stumbling blocks are real, and it is up to each scientist to identify and apply the techniques that work best for them. The responses have been edited for clarity and brevity.