Editors of the journal ranked cancer immunotherapy, a type of treatment that pushes the immune system to attack tumors, at the top of their list of scientific achievements this past year.

We each have trillions of microbial hitchhikers living in and on our bodies. These symbiotic organisms have co-evolved with us over millions of years and increasingly are being seen as essential to our health and well being, researchers said at the 2012 Abelson Symposium at AAAS.

The effort to understand the human microbiome—the full complement of 4 million or more genes contained in the microbial community we each harbor—is one of the hottest fields of scientific research.