For two decades, scientists and doctors have relied on blood types to categorize patients. Depending on whether one is blood type A, B, AB, or O, doctors could alter their treatment to increase their chances of a successful procedure. But there's a new way for people to be categorized medically — gut bacteria. New research shows that there are three distinct ecosystems in people's guts that could have direct effects of people's heath. We talk with Carl Zimmer, science reporter for our partner The New York Times, who reported on this story in yesterday's paper.

Why do we smile? Not only do scientists believe they may have discovered the answer to that question, but also to how we perceive the smile. Carl Zimmer, science writer for The New York Times, has the details of this new study to be published in Behavioral and Brain Sciences.

Summer brings warm evenings dotted by the light of fireflies. The apparently serene scene is full of murder, deception, and secret trysts as the fireflies communicate with each other and try to mate. Joining The Takeaway with more on the passionate life of the firefly is science writer Carl Zimmer. You can read Zimmer's New York Times article on fireflies in today's Science Times, "Blink Twice if You Like Me".