To understand the origins of pain, ask a flatworm
Experiments in planarians identify a chemical middleman that triggers the body’s ouch detectors
![Schmidtea mediterranea](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2017/10/101617_ls_worm_feat_free.jpg?fit=860%2C460&ssl=1)
DANGER DETECTOR In planarians (Schmidtea mediterranea shown), a protein called TRPA1 detects hydrogen peroxide, a molecule produced when cells are damaged. These new results give hints about the evolution of human pain.
Chris Petersen/Northwestern University