Last year it was easy to choose a story to lead our annual Top 25 list. The discovery of the Higgs boson was a watershed moment, ending a decades-long quest by thousands of physicists to fully describe the subatomic realm.
This year, nothing so momentous came to pass. But science isn’t just about dramatic announcements and tremendous technical feats. Anyone who reads Science News regularly appreciates that great new insights often arise from countless little bits and pieces of new knowledge. This year, careful readers may have noticed a steady accumulation of revelations about the bacterial communities that call the human body home. It has long been known that those microbes are essential to processes like extracting nutrients from food and fighting off their less benign brethren. But this year a growing body of research demonstrated that bacteria engage their hosts so vigorously that in some situations, scientists are left wondering which party is the tail and which is the dog.
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Human evolution has also produced an impressive body of new knowledge, though some of it only deepens existing mysteries. For example, the oldest hominid DNA ever analyzed linked 400,000-year-old bones from Spain not to the Neandertals that later dominated the region, but to mysterious early hominids known from sites thousands of kilometers to the east. It will probably be a few more years before anyone can explain what is becoming an increasingly controversial era of human evolution.
This year also demonstrated that big findings can be big letdowns. After a spectacular landing on Mars in August 2012, the Curiosity rover looked for elevated atmospheric methane concentrations that would have been telltale evidence for the presence of microbial life. Anything over a few parts per billion would have given us a clear choice for 2013’s top story. But Curiosity detected an average methane concentration of only 0.18 ppb, a finding that landed it in 17th place.
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