Sometimes breakthroughs are only apparent in retrospect. Not so with landing a spacecraft on a comet, hands down the biggest science news of 2014. Despite losing power, the Philae lander managed to accomplish much of its primary mission, and there's a good chance it will wake up again in 2015 as summer comes to the comet and more sunlight hits its solar panels.

In January, scientists reported what seemed like a huge breakthrough: a simple way to turn almost any kind of cell into stem cells by exposing them to acid or other stresses. As other scientists tried to replicate the findings, the story quickly unraveled in tragic fashion. The lead researcher, Haruko Obokata (above), was found guilty of misconduct, the papers were retracted, and her supervisor and co-author hanged himself.

In March, astrophysicists announced they’d detected the telltale signature of gravitational waves, ripples in space and time created almost immediately after the Big Bang. This would've confirmed cosmic inflation, the theory that the universe expanded extremely rapidly in the first moments of existence. But, follow-up analysis suggests the signal could have come from dust. More analysis is needed, but "the discovery of the century" is in doubt.

This year scientists created cells with 6-letter DNA, the culmination of a 15-year effort. Expanding the genetic code to include two new letters not found in nature could allow researchers to create (or evolve) new proteins and other biologically active molecules that would be impossible to synthesize by other means.

In type 1 diabetes, the immune system destroys pancreatic cells that make insulin, a hormone that prompts cells to absorb glucose from the blood. In the more common type 2 diabetes, these "beta cells" underperform. After decades of frustration, scientists finally succeeded this year in creating human beta cells from embryonic stem cells, and used them to ameliorate diabetes in mice. Human trials are still a few years off.

A team of Chinese researchers reported the first-ever live births of monkeys genetically engineered with a new gene-editing system called CRISPR/Cas9. The technique may herald an age of custom-designed research monkeys, perhaps producing better models of human disease. It also raises profound ethical questions about how we treat these intelligent, emotional creatures.

In June, laboratory mistakes exposed around 75 US researchers to anthrax. One month later, a routine laboratory cleanup at the NIH turned up 16 misplaced vials of smallpox in a storage closet. Nobody was sickened, but the resulting outcry pushed the Obama administration to suspend funding for controversial research that intentionally makes diseases like bird flu and SARS more virulent.

The origins of cave painting were long traced to Stone Age inhabitants of Europe. The discovery of 40,000-year-old Indonesian cave paintings this year suggests the first humans to leave Africa were artistic, too. And a 500,000-year-old shell carved by Homo erectus shows how cognitively sophisticated they were. The notion of Homo sapiens as uniquely smart and creative is up for revision.

This year scientists discovered a giant virus buried nearly 100 feet under the Siberian permafrost. At 1.5 micrometers, it's bigger than some bacteria and 10 to 100 times bigger than a typical virus. And despite being frozen for more than 30,000 years, it's still infectious---for amoeba.

The number of wild animals on the planet has decreased by 50 percent in the past 40 years, researchers from the World Wildlife Fund and Zoological Society of London reported this year. It's not just species going extinct; thanks to habitat loss, hunting and other human-driven causes, there's less of what remains.

Late in 2013, a two-year-old boy in a small Guinean village fell sick from Ebola. Less than a year later, thousands of west Africans were dead. The outbreak's lessons are ongoing: the irrationality of westerners fearing contagion, the dangers of relying on pharmaceutical companies to develop treatments for rare but potentially devastating diseases, the importance of local public health systems to global well-being.

Science got more affordable this year. Scientists at Stanford developed a microscope that can be built out of paper for less than $1 and a hand-crank chemistry kit that could be used for teaching or environmental testing in developing countries. The price of sequencing a human genome dropped to $1,000. You still need a $10 million machine, but $1,000 genomes are a notable landmark on the way to personalized genomic medicine.